diff --git a/jsonschema-core.md b/jsonschema-core.md new file mode 100644 index 00000000..e9f38b54 --- /dev/null +++ b/jsonschema-core.md @@ -0,0 +1,4050 @@ +--- +v: 3 +docname: draft-bhutton-json-schema-01 +cat: info +submissiontype: IETF +title: 'JSON Schema: A Media Type for Describing JSON Documents' +abbrev: JSON Schema +wg: Internet Engineering Task Force +kw: JSON +date: 2023 +author: +- role: editor + ins: A. Wright + name: Austin Wright + org: '' + email: aaa@bzfx.net +- role: editor + ins: H. Andrews + name: Henry Andrews + org: '' + email: andrews_henry@yahoo.com +- role: editor + ins: B. Hutton + name: Ben Hutton + org: Postman + email: ben@jsonschema.dev + uri: https://jsonschema.dev +- ins: G. Dennis + name: Greg Dennis + org: '' + email: gregsdennis@yahoo.com + uri: https://github.com/gregsdennis +normative: + RFC3986: + RFC3987: + RFC6839: + RFC6901: + RFC8259: + W3C.REC-ldp-20150226: + ecma262: + target: https://www.ecma-international.org/ecma-262/11.0/index.html + title: ECMA-262, 11th edition specification + author: + - org: '' + date: 2020-06 +informative: + RFC6596: + RFC7049: + RFC7231: + RFC8288: + W3C.WD-fragid-best-practices-20121025: + W3C.REC-xptr-framework-20030325: + json-schema-validation: + title: 'JSON Schema Validation: A Vocabulary for Structural Validation of JSON' + author: + - ins: A. Wright + org: '' + - ins: H. Andrews + org: '' + - ins: B. Hutton + org: '' + date: 2022-06 + seriesinfo: + Internet-Draft: draft-bhutton-json-schema-validation-01 + json-hyper-schema: + title: 'JSON Hyper-Schema: A Vocabulary for Hypermedia Annotation of JSON' + author: + - ins: H. Andrews + org: '' + - ins: A. Wright + org: '' + date: 2017-11 + seriesinfo: + Internet-Draft: draft-handrews-json-schema-hyperschema-02 + xml-names: + target: http://www.w3.org/TR/2006/REC-xml-names11-20060816 + title: Namespaces in XML 1.1 (Second Edition) + author: + - role: editor + name: Tim Bray + org: Textuality + email: tbray@textuality.com + - role: editor + name: Dave Hollander + org: Contivo, Inc. + email: dmh@contivo.com + - role: editor + name: Andrew Layman + org: Microsoft + email: andrewl@microsoft.com + - role: editor + name: Richard Tobin + org: University of Edinburgh and Markup Technology Ltd + email: richard@cogsci.ed.ac.uk + date: 2006-08 + +--- abstract + + +JSON Schema defines the media type "application/schema+json", a JSON-based +format +for describing the structure of JSON data. +JSON Schema asserts what a JSON document must look like, +ways to extract information from it, +and how to interact with it. +The "application/schema-instance+json" media type provides additional +feature-rich integration with "application/schema+json" beyond what can be +offered +for "application/json" documents. + +--- note_Note_to_Readers + +The issues list for this draft can be found at [](https://github.com/json-schema-org/json-schema-spec/issues). + +For additional information, see [](https://json-schema.org/). + +To provide feedback, use this issue tracker, the communication methods listed +on the +homepage, or email the document editors. + +--- middle + +# Introduction + +JSON Schema is a JSON media type for defining the structure of JSON data. +JSON Schema +is intended to define validation, documentation, hyperlink navigation, and +interaction +control of JSON data. + +This specification defines JSON Schema core terminology and mechanisms, including +pointing to another JSON Schema by reference, +dereferencing a JSON Schema reference, +specifying the dialect being used, +specifying a dialect's vocabulary requirements, +and defining the expected output. + +Other specifications define the vocabularies that perform assertions about +validation, +linking, annotation, navigation, and interaction. + + +# Conventions and Terminology + +{::boilerplate bcp14-tagged} + +The terms "JSON", "JSON text", "JSON value", "member", "element", "object", +"array", +"number", "string", "boolean", "true", "false", and "null" in this document +are to +be interpreted as defined in [RFC 8259](#RFC8259). + + +# Overview + +This document proposes a new media type "application/schema+json" to identify +a JSON +Schema for describing JSON data. +It also proposes a further optional media type, "application/schema-instance+json", +to provide additional integration features. +JSON Schemas are themselves JSON documents. +This, and related specifications, define keywords allowing authors to describe +JSON +data in several ways. + +JSON Schema uses keywords to assert constraints on JSON instances or annotate +those +instances with additional information. Additional keywords are used to apply +assertions and annotations to more complex JSON data structures, or based +on +some sort of condition. + +To facilitate re-use, keywords can be organized into vocabularies. A vocabulary +consists of a list of keywords, together with their syntax and semantics. +A dialect is defined as a set of vocabularies and their required support +identified in a meta-schema. + +JSON Schema can be extended either by defining additional vocabularies, +or less formally by defining additional keywords outside of any vocabulary. +Unrecognized individual keywords simply have their values collected as annotations, +while the behavior with respect to an unrecognized vocabulary can be controlled +when declaring which vocabularies are in use. + +This document defines a core vocabulary that MUST be supported by any +implementation, and cannot be disabled. Its keywords are each prefixed +with a "$" character to emphasize their required nature. This vocabulary +is essential to the functioning of the "application/schema+json" media +type, and is used to bootstrap the loading of other vocabularies. + +Additionally, this document defines a RECOMMENDED vocabulary of keywords +for applying subschemas conditionally, and for applying subschemas to +the contents of objects and arrays. Either this vocabulary or one very +much like it is required to write schemas for non-trivial JSON instances, +whether those schemas are intended for assertion validation, annotation, +or both. While not part of the required core vocabulary, for maximum +interoperability this additional vocabulary is included in this document +and its use is strongly encouraged. + +Further vocabularies for purposes such as structural validation or +hypermedia annotation are defined in other documents. These other +documents each define a dialect collecting the standard sets of +vocabularies needed to write schemas for that document's purpose. + + +# Definitions + +## JSON Document + +A JSON document is an information resource (series of octets) described by +the +application/json media type. + +In JSON Schema, the terms "JSON document", "JSON text", and "JSON value" +are +interchangeable because of the data model it defines in {{data-model}}. + +JSON Schema is only defined over JSON documents. However, any document or +memory +structure that can be parsed into or processed according to the JSON Schema +data +model can be interpreted against a JSON Schema, including media types like [CBOR](#RFC7049). + + +## Instance + +A JSON document to which a schema is applied is known as an "instance". + +JSON Schema is defined over "application/json" or compatible documents, +including media types with the "+json" structured syntax suffix. + +Among these, this specification defines the "application/schema-instance+json" +media type which defines handling for fragments in the IRI. + +### Instance Data Model {#data-model} + +JSON Schema interprets documents according to a data model. A JSON value +interpreted according to this data model is called an "instance". + +An instance has one of six primitive types, and a range of possible values +depending on the type: + +null +: A JSON "null" value + +boolean +: A "true" or "false" value, from the JSON "true" or "false" value + +object +: An unordered set of properties mapping a string to an instance, from the + JSON "object" value + +array +: An ordered list of instances, from the JSON "array" value + +number +: An arbitrary-precision, base-10 decimal number value, from the JSON "number" + value + +string +: A string of Unicode code points, from the JSON "string" value + + +Whitespace and formatting concerns, including different lexical +representations of numbers that are equal within the data model, are thus +outside the scope of JSON Schema. JSON Schema [vocabularies](#vocabulary) that wish +to work with such differences in lexical representations SHOULD define +keywords to precisely interpret formatted strings within the data model +rather than relying on having the original JSON representation Unicode +characters available. + +Since an object cannot have two properties with the same key, behavior for +a +JSON document that tries to define two properties with +the same key in a single object is undefined. + +Note that JSON Schema vocabularies are free to define their own extended +type system. This should not be confused with the core data model types +defined here. As an example, "integer" is a reasonable type for a +vocabulary to define as a value for a keyword, but the data model +makes no distinction between integers and other numbers. + + +### Instance Equality + +Two JSON instances are said to be equal if and only if they are of the same +type +and have the same value according to the data model. Specifically, this means: + +* both are null; or + +* both are true; or + +* both are false; or + +* both are strings, and are the same codepoint-for-codepoint; or + +* both are numbers, and have the same mathematical value; or + +* both are arrays, and have an equal value item-for-item; or + +* both are objects, and each property in one has exactly one property with + a key equal to the other's, and that other property has an equal + value. + + +Implied in this definition is that arrays must be the same length, +objects must have the same number of members, +properties in objects are unordered, +there is no way to define multiple properties with the same key, +and mere formatting differences (indentation, placement of commas, trailing +zeros) are insignificant. + + +### Non-JSON Instances + +It is possible to use JSON Schema with a superset of the JSON Schema data +model, +where an instance may be outside any of the six JSON data types. + +In this case, annotations still apply; but most validation keywords will +not be useful, +as they will always pass or always fail. + +A custom vocabulary may define support for a superset of the core data model. +The schema itself may only be expressible in this superset; +for example, to make use of the "const" keyword. + + + +## JSON Schema Documents {#schema-document} + +A JSON Schema document, or simply a schema, is a JSON document used to describe +an instance. +A schema can itself be interpreted as an instance, but SHOULD always be given +the media type "application/schema+json" rather than +"application/schema-instance+json". The "application/schema+json" media +type is defined to offer a superset of the +fragment identifier syntax and semantics provided by +"application/schema-instance+json". + +A JSON Schema MUST be an object or a boolean. + +### JSON Schema Objects and Keywords + +Object properties that are applied to the instance are called keywords, +or schema keywords. Broadly speaking, keywords fall into one +of five categories: + + +identifiers +: control schema identification through setting a IRI + for the schema and/or changing how the base IRI is determined + +assertions +: produce a boolean result when applied to an instance + +annotations +: attach information to an instance for application use + +applicators +: apply one or more subschemas to a particular location + in the instance, and combine or modify their results + +reserved locations +: do not directly affect results, but reserve a place + for a specific purpose to ensure interoperability + +Keywords may fall into multiple categories, although applicators +SHOULD only produce assertion results based on their subschemas' +results. They should not define additional constraints independent +of their subschemas. + +Keywords which are properties within the same schema object are referred +to as adjacent keywords. + +Extension keywords, meaning those defined outside of this document +and its companions, are free to define other behaviors as well. + +A JSON Schema MAY contain properties which are not schema keywords or are +not recognized as schema keywords. +The behavior of such keywords is governed by {{unrecognized}}. + +An empty schema is a JSON Schema with no properties. + + +### Boolean JSON Schemas + +The boolean schema values "true" and "false" are trivial schemas that +always produce themselves as assertion results, regardless of the +instance value. They never produce annotation results. + +These boolean schemas exist to clarify schema author intent and +facilitate schema processing optimizations. They behave identically +to the following schema objects (where "not" is part of the +subschema application vocabulary defined in this document). + + +true +: Always passes validation, as if the empty schema {} + +false +: Always fails validation, as if the schema { "not": {} } + +While the empty schema object is unambiguous, there are many +possible equivalents to the "false" schema. Using the boolean +values ensures that the intent is clear to both human readers +and implementations. + + +### Schema Vocabularies + +A schema vocabulary, or simply a vocabulary, is a set of keywords, +their syntax, and their semantics. A vocabulary is generally organized +around a particular purpose. Different uses of JSON Schema, such +as validation, hypermedia, or user interface generation, will +involve different sets of vocabularies. + +Vocabularies are the primary unit of re-use in JSON Schema, as schema +authors can indicate what vocabularies are required or optional in +order to process the schema. Since vocabularies are identified by IRIs +in the meta-schema, generic implementations can load extensions to support +previously unknown vocabularies. While keywords can be supported outside +of any vocabulary, there is no analogous mechanism to indicate individual +keyword usage. + +A schema vocabulary can be defined by anything from an informal description +to a standards proposal, depending on the audience and interoperability +expectations. In particular, in order to facilitate vocabulary use within +non-public organizations, a vocabulary specification need not be published +outside of its scope of use. + + +### Meta-Schemas + +A schema that itself describes a schema is called a meta-schema. +Meta-schemas are used to validate JSON Schemas and specify which vocabularies +they are using. + +Typically, a meta-schema will specify a set of vocabularies, and validate +schemas that conform to the syntax of those vocabularies. However, meta-schemas +and vocabularies are separate in order to allow meta-schemas to validate +schema conformance more strictly or more loosely than the vocabularies' +specifications call for. Meta-schemas may also describe and validate +additional keywords that are not part of a formal vocabulary. + + +### Root Schema and Subschemas and Resources {#root} + +A JSON Schema resource is a schema which is [canonically](#RFC6596) +identified by an [absolute IRI](#RFC3987). Schema resources MAY +also be identified by IRIs, including IRIs with fragments, +if the resulting secondary resource (as defined by +[section 3.5 of RFC 3986](#RFC3986)) is identical +to the primary resource. This can occur with the empty fragment, +or when one schema resource is embedded in another. Any such IRIs +with fragments are considered to be non-canonical. + +The root schema is the schema that comprises the entire JSON document +in question. The root schema is always a schema resource, where the +IRI is determined as described in {{initial-base}}.[^CREF1] + +[^CREF1]: Note that documents that embed schemas in another format will not + have a root schema resource in this sense. Exactly how such usages + fit with the JSON Schema document and resource concepts will be + clarified in a future draft. + + +Some keywords take schemas themselves, allowing JSON Schemas to be nested: + +~~~~ json +{ + "title": "root", + "items": { + "title": "array item" + } +} +~~~~ + +In this example document, the schema titled "array item" is a subschema, +and the schema titled "root" is the root schema. + +As with the root schema, a subschema is either an object or a boolean. + +As discussed in {{id-keyword}}, a JSON Schema document +can contain multiple JSON Schema resources. When used without qualification, +the term "root schema" refers to the document's root schema. In some +cases, resource root schemas are discussed. A resource's root schema +is its top-level schema object, which would also be a document root schema +if the resource were to be extracted to a standalone JSON Schema document. + +Whether multiple schema resources are embedded or linked with a reference, +they are processed in the same way, with the same available behaviors. + + + + +# Fragment Identifiers {#fragments} + +In accordance with section 3.1 of [RFC 6839](#RFC6839), +the syntax and semantics of fragment identifiers specified for +any +json media type SHOULD be as specified for "application/json". +(At publication of this document, there is no fragment identification +syntax defined for "application/json".) + +Additionally, the "application/schema+json" media type supports two +fragment identifier structures: plain names and JSON Pointers. +The "application/schema-instance+json" media type supports one +fragment identifier structure: JSON Pointers. + +The use of JSON Pointers as IRI fragment identifiers is described in [RFC 6901](#RFC6901). +For "application/schema+json", which supports two fragment identifier syntaxes, +fragment identifiers matching the JSON Pointer syntax, including the empty +string, +MUST be interpreted as JSON Pointer fragment identifiers. + +Per the W3C's [best practices for fragment identifiers](#W3C.WD-fragid-best-practices-20121025), +plain name fragment identifiers in "application/schema+json" are reserved +for referencing +locally named schemas. + +Plain name fragments MUST start with a letter ([A-Za-z]) or underscore ("_"), +followed by any number of letters, digits ([0-9]), hyphens ("-"), +underscores ("_"), and periods ("."). This matches the US-ASCII part of +XML's [NCName production](#xml-names), which allows for compatibility +with the recommended plain name [syntax](#W3C.REC-xptr-framework-20030325) for +XML-based media types. + +All fragment identifiers that do +not match the JSON Pointer syntax MUST be interpreted as +plain name fragment identifiers. + +Defining and referencing a plain name fragment identifier within an +"application/schema+json" document are specified +in the ["$anchor" keyword](#anchor) section. + + +# General Considerations + +## Range of JSON Values + +An instance may be any valid JSON value as defined by [JSON](#RFC8259). +JSON Schema imposes no restrictions on type: JSON Schema can describe any +JSON +value, including, for example, null. + + +## Programming Language Independence {#language} + +JSON Schema is programming language agnostic, and supports the full range +of +values described in the data model. +Be aware, however, that some languages and JSON parsers may not be able to +represent in memory the full range of values describable by JSON. + + +## Mathematical Integers {#integers} + +Some programming languages and parsers use different internal representations +for floating point numbers than they do for integers. + +For consistency, integer JSON numbers SHOULD NOT be encoded with a fractional +part. + + +## Regular Expressions {#regex} + +Keywords MAY use regular expressions to express constraints, or constrain +the instance value to be a regular expression. +These regular expressions SHOULD be valid according to the regular expression +dialect described in [ECMA-262, section 21.2.1](#ecma262). + +Unless otherwise specified by a keyword, regular expressions MUST NOT be +considered to be implicitly anchored at either end. All regular expression +keywords in this specification and its companion documents are un-anchored. + +Regular expressions SHOULD be built with the "u" flag (or equivalent) to +provide +Unicode support, or processed in such a way which provides Unicode support +as +defined by ECMA-262. + +Furthermore, given the high disparity in regular expression constructs support, +schema authors SHOULD limit themselves to the following regular expression +tokens: + +* individual Unicode characters, as defined by the [JSON specification](#RFC8259); + +* simple character classes ([abc]), range character classes ([a-z]); + +* complemented character classes (\[^abc], \[^a-z]); + +* simple quantifiers: "+" (one or more), "\*" (zero or more), "?" (zero or + one), and their lazy versions ("+?", "\*?", "??"); + +* range quantifiers: "{x}" (exactly x occurrences), "{x,y}" (at least x, at + most y, occurrences), {x,} (x occurrences or more), and their lazy + versions; + +* the beginning-of-input ("^") and end-of-input ("$") anchors; + +* simple grouping ("(...)") and alternation ("\|"). + + +Finally, implementations MUST NOT take regular expressions to be +anchored, neither at the beginning nor at the end. This means, for instance, +the pattern "es" matches "expression". + + +## Extending JSON Schema {#extending} + +Additional schema keywords and schema vocabularies MAY be defined +by any entity. Save for explicit agreement, schema authors SHALL NOT +expect these additional keywords and vocabularies to be supported by +implementations that do not explicitly document such support. + +Implementations MAY provide the ability to register or load handlers +for vocabularies that they do not support directly. The exact mechanism +for registering and implementing such handlers is implementation-dependent. + +### Explicit annotation keywords {#explicit-annotation} + +The values of keywords which begin with "x-" MUST be collected as annotations. + +Keywords which begin with "x-" symbol MUST NOT affect evaluation +of a schema in any way other than annotation collection. + +Consequently, the "x-" prefix is reserved for this purpose, and +extension vocabularies MUST NOT define any keywords which begin +with this prefix. + + +### Handling of unrecognized or unsupported keywords {#unrecognized} + +Implementations SHOULD treat keywords they do not recognize, or that +they recognize but do not support, as annotations, where the value of +the keyword is the value of the annotation. Whether an implementation +collects these annotations or not, they MUST otherwise ignore the keywords. + + + + +# Keyword Behaviors + +JSON Schema keywords fall into several general behavior categories. +Assertions validate that an instance satisfies constraints, producing +a boolean result. Annotations attach information that applications +may use in any way they see fit. +Applicators apply subschemas to parts of the instance and combine +their results. + +Extension keywords SHOULD stay within these categories, keeping in mind +that annotations in particular are extremely flexible. Complex behavior +is usually better delegated to applications on the basis of annotation +data than implemented directly as schema keywords. However, extension +keywords MAY define other behaviors for specialized purposes. + +Evaluating an instance against a schema involves processing all of the +keywords in the schema against the appropriate locations within the instance. +Typically, applicator keywords are processed until a schema object with no +applicators (and therefore no subschemas) is reached. The appropriate +location in the instance is evaluated against the assertion and +annotation keywords in the schema object. The interactions of those +keyword results to produce the schema object results are governed by +{{annot-assert}}, while the relationship of subschema results to the +results of the applicator keyword that applied them is described by +{{applicators}}. + +Evaluation of a parent schema object can complete once all of its +subschemas have been evaluated, although in some circumstances evaluation +may be short-circuited due to assertion results. When annotations are +being collected, some assertion result short-circuiting is not possible +due to the need to examine all subschemas for annotation collection, including +those that cannot further change the assertion result. + +## Lexical Scope and Dynamic Scope {#scopes} + +While most JSON Schema keywords can be evaluated on their own, +or at most need to take into account the values or results of +adjacent keywords in the same schema object, a few have more +complex behavior. + +The lexical scope of a keyword is determined by the nested JSON +data structure of objects and arrays. The largest such scope +is an entire schema document. The smallest scope is a single +schema object with no subschemas. + +Keywords MAY be defined with a partial value, such as a IRI-reference, +which must be resolved against another value, such as another +IRI-reference or a full IRI, which is found through the lexical +structure of the JSON document. The "$id", "$ref", and +"$dynamicRef" core keywords, and the "base" JSON Hyper-Schema +keyword, are examples of this sort of behavior. + +Note that some keywords, such as "$schema", apply to the lexical +scope of the entire schema resource, and therefore MUST only +appear in a schema resource's root schema. + +Other keywords may take into account the dynamic scope that +exists during the evaluation of a schema, typically together +with an instance document. +The outermost dynamic scope is the schema object at +which processing begins, even if it is not a schema resource root. +The path from this root schema to any particular keyword (that +includes any "$ref" and "$dynamicRef" keywords that may have +been resolved) is considered the keyword's "evaluation path." + +Lexical and dynamic scopes align until a reference keyword +is encountered. While following the reference keyword moves processing +from one lexical scope into a different one, from the perspective +of dynamic scope, following a reference is no different from descending +into a subschema present as a value. A keyword on the far side of +that reference that resolves information through the dynamic scope +will consider the originating side of the reference to be their +dynamic parent, rather than examining the local lexically enclosing parent. + +The concept of dynamic scope is primarily used with "$dynamicRef" and +"$dynamicAnchor", and should be considered an advanced feature +and used with caution when defining additional keywords. It also appears +when reporting errors and collected annotations, as it may be possible +to revisit the same lexical scope repeatedly with different dynamic +scopes. In such cases, it is important to inform the user of the +evaluation path that produced the error or annotation. + + +## Keyword Interactions + +Keyword behavior MAY be defined in terms of the annotation results +of [subschemas](#root) and/or adjacent keywords +(keywords within the same schema object) and their subschemas. +Such keywords MUST NOT result in a circular dependency. +Keywords MAY modify their behavior based on the presence or absence +of another keyword in the same [schema object](#schema-document). + + +## Default Behaviors {#default-behaviors} + +A missing keyword MUST NOT produce a false assertion result, MUST +NOT produce annotation results, and MUST NOT cause any other schema +to be evaluated as part of its own behavioral definition. +However, given that missing keywords do not contribute annotations, +the lack of annotation results may indirectly change the behavior +of other keywords. + +In some cases, the missing keyword assertion behavior of a keyword is +identical to that produced by a certain value, and keyword definitions +SHOULD note such values where known. However, even if the value which +produces the default behavior would produce annotation results if +present, the default behavior still MUST NOT result in annotations. + +Because annotation collection can add significant cost in terms of both +computation and memory, implementations MAY opt out of this feature. +Keywords that are specified in terms of collected annotations SHOULD +describe reasonable alternate approaches when appropriate. +This approach is demonstrated by the +"{{<. + +The current IRI for the corresponding meta-schema is: [](https://json-schema.org/draft/next/meta/core). + +The "$" prefix is reserved for use by the Core vocabulary. +Vocabulary extensions MUST NOT define new keywords that begin with "$". + +## Meta-Schemas and Vocabularies {#vocabulary} + +Two concepts, meta-schemas and vocabularies, are used to inform an implementation +how to interpret a schema. Every schema has a meta-schema, which can be +declared +using the "$schema" keyword. + +The meta-schema serves two purposes: + + +Declaring the vocabularies in use +: The "$vocabulary" keyword, when it appears in a meta-schema, declares + which vocabularies are available to be used in schemas that refer + to that meta-schema. Vocabularies define keyword semantics, + as well as their general syntax. + +Describing valid schema syntax +: A schema MUST successfully validate against its meta-schema, which + constrains the syntax of the available keywords. The syntax described + is expected to be compatible with the vocabularies declared; while + it is possible to describe an incompatible syntax, such a meta-schema + would be unlikely to be useful. + +Meta-schemas are separate from vocabularies to allow for +vocabularies to be combined in different ways, and for meta-schema authors +to impose additional constraints such as forbidding certain keywords, or +performing unusually strict syntactical validation, as might be done +during a development and testing cycle. Each vocabulary typically identifies +a meta-schema consisting only of the vocabulary's keywords. + +Meta-schema authoring is an advanced usage of JSON Schema, so the design +of +meta-schema features emphasizes flexibility over simplicity. + +### The "$schema" Keyword {#keyword-schema} + +The "$schema" keyword is both used as a JSON Schema dialect identifier and +as the identifier of a resource which is itself a JSON Schema, which describes +the +set of valid schemas written for this particular dialect. + +The value of this keyword MUST be a [IRI](#RFC3987) (containing a scheme) and this IRI MUST be normalized. +The current schema MUST be valid against the meta-schema identified by this +IRI. + +If this IRI identifies a retrievable resource, that resource SHOULD be of +media type "application/schema+json". + +The "$schema" keyword SHOULD be used in the document root schema object, +and MAY be used in the root schema objects of embedded schema resources. +It MUST NOT appear in non-resource root schema objects. If absent from +the document root schema, the resulting behavior is implementation-defined, +but MUST fall within the following options: + +* Refuse to process the schema, as with unsupported required + vocabularies + +* Assume a specific, documented meta-schema + +* Document the process by which it examines the schema and determines + which of a specific set of meta-schemas to assume + + +Values for this property are defined elsewhere in this and other documents, +and by other parties. + + +### The "$vocabulary" Keyword + +The "$vocabulary" keyword is used in meta-schemas to identify the +vocabularies available for use in schemas described by that meta-schema, +and whether each vocabulary is required or optional. Together, this +information forms a dialect. + +The value of this keyword MUST be an object. The property names in the +object MUST be IRIs (containing a scheme) and each IRI MUST be normalized. +Each IRI that appears as a property name identifies a specific set of +keywords and their semantics. + +The IRI MAY be a URL, but the nature of the retrievable resource is +currently undefined, and reserved for future use. Vocabulary authors +MAY use the URL of the vocabulary specification, in a human-readable +media type such as text/html or text/plain, as the vocabulary IRI.[^CREF2] + +[^CREF2]: Vocabulary documents may be added in forthcoming drafts. + For now, identifying the keyword set is deemed sufficient as that, + along with meta-schema validation, is how the current "vocabularies" + work today. Any future vocabulary document format will be specified + as a JSON document, so using text/html or other non-JSON formats + in the meantime will not produce any future ambiguity. + + +The values of the object properties MUST be booleans. +If the value is true, then the vocabulary MUST be considered to be required. +If the value is false, then the vocabulary MUST be considered to be optional. + +#### Required, optional, and omitted vocabularies + +A schema is said to use a dialect and its constituent vocabularies if it +is +associated with a meta-schema defining the dialect with "$vocabulary", +either through "$schema", through appropriately defined media type parameters +or link relation types, or through documented default implementation-defined +behavior in the absence of an explicit meta-schema. If a meta-schema +does not contain "$vocabulary", the set of vocabularies in use is determined +according to {{default-vocabs}}. + +Any vocabulary in use by a schema and understood by the implementation +MUST be processed in a manner consistent with the semantic definitions +contained within the vocabulary, regardless of whether that vocabulary +is required or optional. + +Any vocabulary that is not present in "$vocabulary" MUST NOT be made +available for use in schemas described by that meta-schema, except for +the core vocabulary as specified by the introduction to {{core}}. + +Implementations that do not support a vocabulary required by a schema +MUST refuse to process that schema. + +Implementations that do not support a vocabulary that is optionally used +by a schema SHOULD proceed with processing the schema. The keywords will +be considered to be unrecognized keywords as addressed by {{unrecognized}}. Note that since +the recommended behavior for such keywords is to collect them as +annotations, vocabularies consisting only of annotations will have +the same behavior when used optionally whether the implementation +supports them or not. This allows annotation-only vocabularies to +be supported without custom code, even in implementations that do +not support providing custom code for extension vocabularies. + + +#### Vocabularies are schema resource-scoped + +The "$vocabulary" keyword SHOULD be used in the root schema of any schema +resource intended for use as a meta-schema. It MUST NOT appear in subschemas. + +The "$vocabulary" keyword MUST be ignored in schema resources that +are not being processed as a meta-schema. This allows validating +a meta-schema M against its own meta-schema M' without requiring +the validator to understand the vocabularies declared by M. + + +#### Vocabulary and non-vocabulary keywords + +Keywords from different vocabularies, as well as non-vocabulary +extension keywords, can have identical names. These are not +considered to be the same keyword from the perspective of +enabling or disabling them through "$vocabulary". + +In particular the keywords defined in this specification and its +companion documents MUST be considered to be vocabulary keywords, +with availability governed by "$vocabulary" even in implementations +that do not support any extension vocabularies. + +Guidance regarding vocabularies with identically-named keywords is provided +in {{vocab-practices}}. + + +#### Default vocabularies {#default-vocabs} + +If "$vocabulary" is absent, an implementation MAY determine +behavior based on the meta-schema if it is recognized from the +IRI value of the referring schema's "$schema" keyword. +This is how behavior (such as Hyper-Schema usage) has been +recognized prior to the existence of vocabularies. + +If the meta-schema, as referenced by the schema, is not recognized, +or is missing, then the behavior is implementation-defined. +If the implementation +proceeds with processing the schema, it MUST assume the use of the +core vocabulary. If the implementation is built for a specific purpose, +then it SHOULD assume the use of all of the most relevant vocabularies +for that purpose. + +For example, an implementation that is a validator +SHOULD assume the use of all vocabularies in this +specification and the companion Validation specification. + + +#### Non-inheritability of vocabularies + +Note that the processing restrictions on "$vocabulary" mean that +meta-schemas that reference other meta-schemas using "$ref" or +similar keywords do not automatically inherit the vocabulary +declarations of those other meta-schemas. All such declarations +must be repeated in the root of each schema document intended +for use as a meta-schema. This is demonstrated in [the example meta-schema](#example-meta-schema).[^CREF3] + +[^CREF3]: This requirement allows implementations to find all vocabulary + requirement information in a single place for each meta-schema. + As schema extensibility means that there are endless potential + ways to combine more fine-grained meta-schemas by reference, + requiring implementations to anticipate all possibilities and + search for vocabularies in referenced meta-schemas would + be overly burdensome. + + + + +### Updates to Meta-Schema and Vocabulary IRIs + +Updated vocabulary and meta-schema IRIs MAY be published between +specification drafts in order to correct errors. Implementations +SHOULD consider IRIs dated after this specification draft and +before the next to indicate the same syntax and semantics +as those listed here. + + + +## Base IRI, Anchors, and Dereferencing + +To differentiate between schemas in a vast ecosystem, schemas are +identified by [IRI](#RFC3987), and can embed references +to other schemas by specifying their IRI. + +Several keywords can accept a relative [IRI-reference](#RFC3987), +or a value used to construct a relative IRI-reference. For these keywords, +it is necessary to establish a base IRI in order to resolve the reference. + +### The "$id" Keyword {#id-keyword} + +The "$id" keyword identifies a schema resource with its [canonical](#RFC6596) IRI. + +Note that this IRI is an identifier and not necessarily a network locator. +In the case of a network-addressable URL, a schema need not be downloadable +from its canonical IRI. + +If present, the value for this keyword MUST be a string, and MUST represent +a +valid [IRI-reference](#RFC3987). This IRI-reference +SHOULD be normalized, and MUST resolve to an [absolute-IRI](#RFC3987) (without a fragment). + +The resulting absolute-IRI serves as the base IRI for relative IRI-references +in keywords within the schema resource, in accordance with [RFC 3987 section 6.5](#RFC3987) and [RFC 3986 section 5.1.1](#RFC3986) regarding base IRIs +embedded in content. + +The presence of "$id" in a subschema indicates that the subschema constitutes +a distinct schema resource within a single schema document. Furthermore, +in accordance with [RFC 3987 section 6.5](#RFC3987) and [RFC 3986 section 5.1.2](#RFC3986) regarding +encapsulating entities, if an "$id" in a subschema is a relative +IRI-reference, the base IRI for resolving that reference is the IRI of +the parent schema resource. Note that an "$id" consisting of an empty IRI +or +of the empty fragment only will result in the embedded resource having +the same IRI as the encapsulating resource, which SHOULD be considered +an error per {{duplicate-iris}}. + +If no parent schema object explicitly identifies itself as a resource +with "$id", the base IRI is that of the entire document, as established +by the steps given in the [previous section.](#initial-base) + +#### Identifying the root schema + +The root schema of a JSON Schema document SHOULD contain an "$id" keyword +with an [absolute-IRI](#RFC3987) (containing a scheme, +but no fragment). + + + +### Defining location-independent identifiers {#anchor} + +Using JSON Pointer fragments requires knowledge of the structure of the schema. +When writing schema documents with the intention to provide re-usable +schemas, it may be preferable to use a plain name fragment that is not tied +to +any particular structural location. This allows a subschema to be relocated +without requiring JSON Pointer references to be updated. + +The "$anchor" and "$dynamicAnchor" keywords are used to specify such +fragments. They are identifier keywords that can only be used to create +plain name fragments, rather than absolute IRIs as seen with "$id". + +The base IRI to which the resulting fragment is appended is the canonical +IRI of the schema resource containing the "$anchor" or "$dynamicAnchor" +in question. As discussed in the previous section, this is either the +nearest "$id" in the same or parent schema object, +or the base IRI for the document as determined according to [RFC 3987](#RFC3987) and [RFC 3986](#RFC3986). + +Separately from the usual usage of IRIs, "$dynamicAnchor" +indicates that the fragment is an extension point when used with +the "$dynamicRef" keyword. This low-level, advanced feature +makes it easier to extend recursive schemas such as the meta-schemas, +without imposing any particular semantics on that extension. +See the section on ["$dynamicRef"](#dynamic-ref) for details. + +In most cases, the normal fragment behavior both suffices and +is more intuitive. Therefore it is RECOMMENDED that "$anchor" +be used to create plain name fragments unless there is a clear +need for "$dynamicAnchor". + +If present, the value of these keywords MUST be a string and MUST conform +to the plain name fragment identifier syntax defined in {{fragments}}.[^CREF4] + +[^CREF4]: Note that the anchor string does not include the "#" character, + as it is not a IRI-reference. An "$anchor": "foo" becomes the + fragment "#foo" when used in a IRI. See below for full examples. + + + +### Duplicate schema identifiers {#duplicate-iris} + +A schema MAY (and likely will) have multiple IRIs, but there is no way +for an IRI to identify more than one schema. When multiple schemas +attempt to identify as the same IRI through the use of "$id", "$anchor", +"$dynamicAnchor", or any other mechanism, implementations SHOULD raise +an error condition. Otherwise the result is undefined, and even if +documented will not be interoperable. + + +### Schema References {#references} + +Several keywords can be used to reference a schema which is to be applied +to the +current instance location. "$ref" and "$dynamicRef" are applicator +keywords, applying the referenced schema to the instance. + +As the values of "$ref" and "$dynamicRef" are IRI References, this allows +the possibility to externalise or divide a schema across multiple files, +and provides the ability to validate recursive structures through +self-reference. + +The resolved IRI produced by these keywords is not necessarily a network +locator, only an identifier. A schema need not be downloadable from the +address if it is a network-addressable URL, and implementations SHOULD NOT +assume they should perform a network operation when they encounter +a network-addressable IRI. + +#### Direct References with "$ref" {#ref} + +The "$ref" keyword is an applicator that is used to reference a statically +identified schema. Its results are the results of the referenced schema.[^CREF5] + +[^CREF5]: Note that this definition of how the results are determined means that + other keywords can appear alongside of "$ref" in the same schema object. + + +The value of the "$ref" keyword MUST be a string which is a IRI-Reference. +Resolved against the current IRI base, it produces the IRI of the schema +to apply. This resolution is safe to perform on schema load, as the +process of evaluating an instance cannot change how the reference resolves. + + +#### Dynamic References with "$dynamicRef" {#dynamic-ref} + +The "$dynamicRef" keyword is an applicator that allows for deferring the +full resolution until runtime, at which point it is resolved each time it +is +encountered while evaluating an instance. + +Together with "$dynamicAnchor", "$dynamicRef" implements a cooperative +extension mechanism that is primarily useful with recursive schemas +(schemas that reference themselves). The extension point is defined with +"$dynamicAnchor" and only exhibits runtime dynamic behavior when referenced +with "$dynamicRef". + +The value of the "$dynamicRef" property MUST be a string which is a +IRI-Reference that contains a valid [plain name fragment](#anchor). Resolved against the current IRI base, it indicates +the schema resource used as the starting point for runtime resolution. +This initial resolution is safe to perform on schema load. + +The schema to apply is the outermost schema resource in the [dynamic scope](#scopes) that defines a +"$dynamicAnchor" that matches the plain name fragment in the initially +resolved IRI. + +For a full example using these keyword, see {{recursive-example}}.[^CREF6] + +[^CREF6]: The difference between the hyper-schema meta-schema in pre-2019 + drafts and an this draft dramatically demonstrates the utility + of these keywords. + + + + +### Schema Re-Use With "$defs" {#defs} + +The "$defs" keyword reserves a location for schema +authors to inline re-usable JSON Schemas into a more general schema. +The keyword does not directly affect the validation result. + +This keyword's value MUST be an object. +Each member value of this object MUST be a valid JSON Schema. + +As an example, here is a schema describing an array of positive +integers, where the positive integer constraint is a subschema in +"$defs": + +~~~~ json +{ + "type": "array", + "items": { "$ref": "#/$defs/positiveInteger" }, + "$defs": { + "positiveInteger": { + "type": "integer", + "exclusiveMinimum": 0 + } + } +} +~~~~ + + + +## Comments With "$comment" + +This keyword reserves a location for comments from schema authors +to readers or maintainers of the schema. + +The value of this keyword MUST be a string. Implementations MUST NOT present +this +string to end users. Tools for editing schemas SHOULD support displaying +and +editing this keyword. The value of this keyword MAY be used in debug or +error +output which is intended for developers making use of schemas. + +Schema vocabularies SHOULD allow "$comment" within any object containing +vocabulary keywords. Implementations MAY assume "$comment" is allowed +unless the vocabulary specifically forbids it. Vocabularies MUST NOT +specify any effect of "$comment" beyond what is described in this +specification. + +Tools that translate other media types or programming languages +to and from application/schema+json MAY choose to convert that media type +or +programming language's native comments to or from "$comment" values. +The behavior of such translation when both native comments and "$comment" +properties are present is implementation-dependent. + +Implementations MAY strip "$comment" values at any point during processing. +In particular, this allows for shortening schemas when the size of deployed +schemas is a concern. + +Implementations MUST NOT take any other action based on the presence, absence, +or contents of "$comment" properties. In particular, the value of "$comment" +MUST NOT be collected as an annotation result. + + + +# Loading and Processing Schemas + + + +## Loading a Schema + +### Initial Base IRI {#initial-base} + + [RFC 3987 Section 6.5](#RFC3987) and [RFC 3986 Section 5.1](#RFC3986) defines how to determine the +default base IRI of a document. + +Informatively, the initial base IRI of a schema is the IRI at which it was +found, whether that was a network location, a local filesystem, or any other +situation identifiable by a IRI of any known scheme. + +If a schema document defines no explicit base IRI with "$id" +(embedded in content), the base IRI is that determined per [RFC 3987 Section 6.5](#RFC3987) and [RFC 3986 section 5](#RFC3986). + +If no source is known, or no IRI scheme is known for the source, a suitable +implementation-specific default IRI MAY be used as described in [RFC 3987 Section 6.5](#RFC3987) and [RFC 3986 Section 5.1.4](#RFC3986). It is RECOMMENDED +that implementations document any default base IRI that they assume. + +If a schema object is embedded in a document of another media type, then +the initial base IRI is determined according to the rules of that +media type. + +Unless the "$id" keyword described in an earlier section is present in the +root schema, this base IRI SHOULD be considered the canonical IRI of the +schema document's root schema resource. + + +### Loading a referenced schema + +The use of IRIs to identify remote schemas does not necessarily mean anything +is downloaded, +but instead JSON Schema implementations SHOULD understand ahead of time which +schemas they will be using, +and the IRIs that identify them. + +When schemas are downloaded, +for example by a generic user-agent that does not know until runtime which +schemas to download, +see [Usage for Hypermedia](#hypermedia). + +Implementations SHOULD be able to associate arbitrary IRIs with an arbitrary +schema and/or automatically associate a schema's "$id"-given IRI, depending +on the trust that the validator has in the schema. Such IRIs and schemas +can be supplied to an implementation prior to processing instances, or may +be noted within a schema document as it is processed, producing associations +as shown in {{idExamples}}. + + +### Detecting a Meta-Schema + +Implementations MUST recognize a schema as a meta-schema if it +is being examined because it was identified as such by another +schema's "$schema" keyword. This means that a single schema +document might sometimes be considered a regular schema, and +other times be considered a meta-schema. + +In the case of examining a schema which is its own meta-schema, +when an implementation begins processing it as a regular schema, +it is processed under those rules. However, when loaded a second +time as a result of checking its own "$schema" value, it is treated +as a meta-schema. So the same document is processed both ways in +the course of one session. + +Implementations MAY allow a schema to be explicitly passed as a meta-schema, +for implementation-specific purposes, such as pre-loading a commonly +used meta-schema and checking its vocabulary support requirements +up front. Meta-schema authors MUST NOT expect such features to be +interoperable across implementations. + + + +## Dereferencing + +Schemas can be identified by any IRI that has been given to them, including +a JSON Pointer or their IRI given directly by "$id". In all cases, +dereferencing a "$ref" reference involves first resolving its value as a +IRI reference against the current base IRI per [RFC 3986](#RFC3986). + +If the resulting IRI identifies a schema within the current document, or +within another schema document that has been made available to the implementation, +then that schema SHOULD be used automatically. + +For example, consider this schema: + +~~~~ json +{ + "$id": "https://example.net/root.json", + "type": "array", + "items": { "$ref": "#item" }, + "$defs": { + "single": { + "$anchor": "item", + "type": "object", + "additionalProperties": { "$ref": "other.json" } + } + } +} +~~~~ + +When an implementation encounters the \<#/$defs/single> schema, +it resolves the "$anchor" value as a fragment name against the current +base IRI to form \. + +When an implementation then looks inside the \<#/items> schema, it +encounters the \<#item> reference, and resolves this to +\, which it has seen defined in +this same document and can therefore use automatically. + +When an implementation encounters the reference to "other.json", it resolves +this to \, which is not defined in this +document. If a schema with that identifier has otherwise been supplied to +the implementation, it can also be used automatically.[^CREF7] + +[^CREF7]: What should implementations do when the referenced schema is not known? + Are there circumstances in which automatic network dereferencing is + allowed? A same origin policy? A user-configurable option? In the + case of an evolving API described by Hyper-Schema, it is expected that + new schemas will be added to the system dynamically, so placing an + absolute requirement of pre-loading schema documents is not feasible. + + +### JSON Pointer fragments and embedded schema resources {#embedded} + +Since JSON Pointer IRI fragments are constructed based on the structure +of the schema document, an embedded schema resource and its subschemas +can be identified by JSON Pointer fragments relative to either its own +canonical IRI, or relative to any containing resource's IRI. + +Conceptually, a set of linked schema resources should behave +identically whether each resource is a separate document connected with [schema references](#references), or is structured as +a single document with one or more schema resources embedded as +subschemas. + +Since IRIs involving JSON Pointer fragments relative to the parent +schema resource's IRI cease to be valid when the embedded schema +is moved to a separate document and referenced, applications and schemas +SHOULD NOT use such IRIs to identify embedded schema resources or +locations within them. + +Consider the following schema document that contains another +schema resource embedded within it: + +~~~~ json +{ + "$id": "https://example.com/foo", + "items": { + "$id": "https://example.com/bar", + "additionalProperties": { } + } +} +~~~~ + +The IRI "https://example.com/foo#/items" points to the "items" schema, +which is an embedded resource. The canonical IRI of that schema +resource, however, is "https://example.com/bar". + +For the "additionalProperties" schema within that embedded resource, +the IRI "https://example.com/foo#/items/additionalProperties" points +to the correct object, but that object's IRI relative to its resource's +canonical IRI is "https://example.com/bar#/additionalProperties". + +Now consider the following two schema resources linked by reference +using a IRI value for "$ref": + +~~~~ json +{ + "$id": "https://example.com/foo", + "items": { + "$ref": "bar" + } +} +~~~~ + +~~~~ json +{ + "$id": "https://example.com/bar", + "additionalProperties": { } +} +~~~~ + +Here we see that "https://example.com/bar#/additionalProperties", +using a JSON Pointer fragment appended to the canonical IRI of +the "bar" schema resource, is still valid, while +"https://example.com/foo#/items/additionalProperties", which relied +on a JSON Pointer fragment appended to the canonical IRI of the +"foo" schema resource, no longer resolves to anything. + +Note also that "https://example.com/foo#/items" is valid in both +arrangements, but resolves to a different value. This IRI ends up +functioning similarly to a retrieval IRI for a resource. While this IRI +is valid, it is more robust to use the "$id" of the embedded or referenced +resource unless it is specifically desired to identify the object containing +the "$ref" in the second (non-embedded) arrangement. + +An implementation MAY choose not to support addressing schema resource +contents by IRIs using a base other than the resource's canonical IRI, +plus a JSON Pointer fragment relative to that base. Therefore, schema +authors SHOULD NOT rely on such IRIs, as using them may reduce interoperability.[^CREF8] + +[^CREF8]: This is to avoid requiring implementations to keep track of a whole + stack of possible base IRIs and JSON Pointer fragments for each, + given that all but one will be fragile if the schema resources + are reorganized. Some + have argued that this is easy so there is + no point in forbidding it, while others have argued that it complicates + schema identification and should be forbidden. Feedback on this + topic is encouraged. + After some discussion, we feel that we need to remove the use of + "canonical" in favour of talking about JSON Pointers which reference + across schema resource boundaries as undefined or even forbidden behavior + (https://github.com/json-schema-org/json-schema-spec/issues/937, + https://github.com/json-schema-org/json-schema-spec/issues/1183) + + +Further examples of such non-canonical IRI construction, as well as +the appropriate canonical IRI-based fragments to use instead, +are provided in {{idExamples}}. + + + +## Compound Documents + +A Compound Schema Document is defined as a JSON document (sometimes called +a "bundled" schema) +which has multiple embedded JSON Schema Resources bundled into the same document +to +ease transportation. + +Each embedded Schema Resource MUST be treated as an individual Schema Resource, +following standard +schema loading and processing requirements, including determining vocabulary +support. + +### Bundling + +The bundling process for creating a Compound Schema Document is defined as +taking +references (such as "$ref") to an external Schema Resource and embedding +the referenced +Schema Resources within the referring document. Bundling SHOULD be done in +such a way that +all IRIs (used for referencing) in the base document and any referenced/embedded +documents do not require altering. + +Each embedded JSON Schema Resource MUST identify itself with a IRI using +the "$id" keyword, +and SHOULD make use of the "$schema" keyword to identify the dialect it is +using, in the root of the +schema resource. It is RECOMMENDED that the IRI identifier value of "$id" +be an Absolute IRI. + +When the Schema Resource referenced by a by-reference applicator is bundled, +it is RECOMMENDED that +the Schema Resource be located as a value of a "$defs" object at the containing +schema's root. +The key of the "$defs" for the now embedded Schema Resource MAY be the "$id" +of the bundled schema +or some other form of application defined unique identifer (such as a UUID). +This key is not +intended to be referenced in JSON Schema, but may be used by an application +to aid the +bundling process. + +A Schema Resource MAY be embedded in a location other than "$defs" where +the location is defined +as a schema value. + +A Bundled Schema Resource MUST NOT be bundled by replacing the schema object +from which it was +referenced, or by wrapping the Schema Resource in other applicator keywords. + +In order to produce identical output, references in the containing schema +document to the +previously external Schema Resources MUST NOT be changed, and now resolve +to a schema using the +"$id" of an embedded Schema Resource. Such identical output includes validation +evaluation and IRIs +or paths used in resulting annotations or errors. + +While the bundling process will often be the main method for creating a Compound +Schema Document, +it is also possible and expected that some will be created by hand, potentially +without individual +Schema Resources existing on their own previously. + + +### Differing and Default Dialects + +When multiple schema resources are present in a single document, +schema resources which do not define with which dialect they should be processed +MUST be processed with the same dialect as the enclosing resource. + +Since any schema that can be referenced can also be embedded, embedded schema +resources MAY +specify different processing dialects using the "$schema" values from their +enclosing resource. + + +### Validating + +Given that a Compound Schema Document may have embedded resources which identify +as using different +dialects, these documents SHOULD NOT be validated by applying a meta-schema +to the Compound Schema Document as an instance. It is RECOMMENDED that an +alternate +validation process be provided in order to validate Schema Documents. Each +Schema Resource +SHOULD be separately validated against its associated meta-schema.[^CREF9] + +[^CREF9]: If you know a schema is what's being validated, you can identify if the schemas + is a Compound Schema Document or not, by way of use of "$id", which identifies an + embedded resource when used not at the document's root. + + +A Compound Schema Document in which all embedded resources identify as using +the same +dialect, or in which "$schema" is omitted and therefore defaults to that +of the enclosing resource, +MAY be validated by applying the appropriate meta-schema. + + + +## Caveats + +### Guarding Against Infinite Recursion + +A schema MUST NOT be run into an infinite loop against an instance. For +example, if two schemas "#alice" and "#bob" both have an "allOf" property +that refers to the other, a naive validator might get stuck in an infinite +recursive loop trying to validate the instance. Schemas SHOULD NOT make +use of infinite recursive nesting like this; the behavior is undefined. + + +### References to Possible Non-Schemas {#non-schemas} + +Subschema objects (or booleans) are recognized by their use with known +applicator keywords or with location-reserving keywords such as ["$defs"](#defs) that take one or more subschemas +as a value. These keywords may be "$defs" and the standard applicators +from this document, or extension keywords from a known vocabulary, or +implementation-specific custom keywords. + +Multi-level structures of unknown keywords are capable of introducing +nested subschemas, which would be subject to the processing rules for +"$id". Therefore, having a reference target in such an unrecognized +structure cannot be reliably implemented, and the resulting behavior +is undefined. Similarly, a reference target under a known keyword, +for which the value is known not to be a schema, results in undefined +behavior in order to avoid burdening implementations with the need +to detect such targets.[^CREF10] + +[^CREF10]: These scenarios are analogous to fetching a schema over HTTP + but receiving a response with a Content-Type other than + application/schema+json. An implementation can certainly + try to interpret it as a schema, but the origin server + offered no guarantee that it actually is any such thing. + Therefore, interpreting it as such has security implications + and may produce unpredictable results. + + +Note that single-level custom keywords with identical syntax and +semantics to "$defs" do not allow for any intervening "$id" keywords, +and therefore will behave correctly under implementations that attempt +to use any reference target as a schema. However, this behavior is +implementation-specific and MUST NOT be relied upon for interoperability. + + + +## Associating Instances and Schemas + +### Usage for Hypermedia {#hypermedia} + +JSON has been adopted widely by HTTP servers for automated APIs and robots. +This +section describes how to enhance processing of JSON documents in a more RESTful +manner when used with protocols that support media types and [Web linking](#RFC8288). + +#### Linking to a Schema + +It is RECOMMENDED that instances described by a schema provide a link to +a downloadable JSON Schema using the link relation "describedby", as defined +by [Linked Data Protocol 1.0, section 8.1](#W3C.REC-ldp-20150226). + +In HTTP, such links can be attached to any response using the [Link header](#RFC8288). An example of such a header would be: + +~~~~ +Link: ; rel="describedby" +~~~~ + + +#### Usage Over HTTP + +When used for hypermedia systems over a network, [HTTP](#RFC7231) is frequently the protocol of choice for +distributing schemas. Misbehaving clients can pose problems for server +maintainers if they pull a schema over the network more frequently than +necessary, when it's instead possible to cache a schema for a long period +of +time. + +HTTP servers SHOULD set long-lived caching headers on JSON Schemas. +HTTP clients SHOULD observe caching headers and not re-request documents +within +their freshness period. +Distributed systems SHOULD make use of a shared cache and/or caching proxy. + +Clients SHOULD set or prepend a User-Agent header specific to the JSON Schema +implementation or software product. Since symbols are listed in decreasing +order +of significance, the JSON Schema library name/version should precede the +more +generic HTTP library name (if any). For example: + +~~~~ +User-Agent: product-name/5.4.1 so-cool-json-schema/1.0.2 curl/7.43.0 +~~~~ + +Clients SHOULD be able to make requests with a "From" header so that server +operators can contact the owner of a potentially misbehaving script. + + + + + +# A Vocabulary for Applying Subschemas + +This section defines a vocabulary of applicator keywords that +are RECOMMENDED for use as the basis of other vocabularies. + +Meta-schemas that do not use "$vocabulary" SHOULD be considered to +require this vocabulary as if its IRI were present with a value of true. + +The current IRI for this vocabulary, known as the Applicator vocabulary, +is: +\. + +The current IRI for the corresponding meta-schema is: [](https://json-schema.org/draft/next/meta/applicator). + +## Keyword Independence + +Schema keywords typically operate independently, without +affecting each other's outcomes. + +For schema author convenience, there are some exceptions among the +keywords in this vocabulary: + + +* "additionalProperties", whose behavior is defined in terms of + "properties" and "patternProperties" + +* "items", whose behavior is defined in terms of "prefixItems" + +* "contains", whose behavior is affected by the presence and value of + "minContains" + + +## Keywords for Applying Subschemas in Place {#in-place} + +These keywords apply subschemas to the same location in the instance +as the parent schema is being applied. They allow combining +or modifying the subschema results in various ways. + +Subschemas of these keywords evaluate the instance completely independently +such that the results of one such subschema MUST NOT impact the results of +sibling +subschemas. Therefore subschemas may be applied in +any order. + +### Keywords for Applying Subschemas With Logic {#logic} + +These keywords correspond to logical operators for combining or modifying +the boolean assertion results of the subschemas. They have no direct +impact on annotation collection, although they enable the same annotation +keyword to be applied to an instance location with different values. +Annotation keywords define their own rules for combining such values. + +#### allOf {#allOf} + +This keyword's value MUST be a non-empty array. +Each item of the array MUST be a valid JSON Schema. + +An instance validates successfully against this keyword if it validates +successfully against all schemas defined by this keyword's value. + + +#### anyOf + +This keyword's value MUST be a non-empty array. +Each item of the array MUST be a valid JSON Schema. + +An instance validates successfully against this keyword if it validates +successfully against at least one schema defined by this keyword's value. +Note that when annotations are being collected, all subschemas MUST +be examined so that annotations are collected from each subschema +that validates successfully. + + +#### oneOf + +This keyword's value MUST be a non-empty array. +Each item of the array MUST be a valid JSON Schema. + +An instance validates successfully against this keyword if it validates +successfully against exactly one schema defined by this keyword's value. + + +#### not {#not} + +This keyword's value MUST be a valid JSON Schema. + +An instance is valid against this keyword if it fails to validate +successfully against the schema defined by this keyword. + + + +### Keywords for Applying Subschemas Conditionally {#conditional} + +Three of these keywords work together to implement conditional +application of a subschema based on the outcome of another subschema. +The fourth is a shortcut for a specific conditional case. + +"if", "then", and "else" MUST NOT interact with each other across +subschema boundaries. In other words, an "if" in one +branch of an "allOf" MUST NOT have an impact on a "then" +or "else" in another branch. + +There is no default behavior for "if", "then", or "else" +when they are not present. In particular, they MUST NOT +be treated as if present with an empty schema, and when +"if" is not present, both "then" and "else" MUST be +entirely ignored. + +#### if + +This keyword's value MUST be a valid JSON Schema. + +This validation outcome of this keyword's subschema +has no direct effect on the overall validation +result. Rather, it controls which of the "then" +or "else" keywords are evaluated. + +Instances that successfully validate against this +keyword's subschema MUST also be valid against +the subschema value of the "then" keyword, if +present. + +Instances that fail to validate against this +keyword's subschema MUST also be valid against +the subschema value of the "else" keyword, if +present. + +If [annotations⁠](#annotations) are being collected, they are collected from this +keyword's subschema in the usual way, including when +the keyword is present without either "then" or "else". + + +#### then + +This keyword's value MUST be a valid JSON Schema. + +When "if" is present, and the instance successfully +validates against its subschema, then validation +succeeds against this keyword if the instance also +successfully validates against this keyword's subschema. + +This keyword has no effect when "if" is absent, or +when the instance fails to validate against its +subschema. Implementations MUST NOT evaluate +the instance against this keyword, for either validation +or annotation collection purposes, in such cases. + + +#### else + +This keyword's value MUST be a valid JSON Schema. + +When "if" is present, and the instance fails to +validate against its subschema, then validation +succeeds against this keyword if the instance +successfully validates against this keyword's subschema. + +This keyword has no effect when "if" is absent, or +when the instance successfully validates against its +subschema. Implementations MUST NOT evaluate +the instance against this keyword, for either validation +or annotation collection purposes, in such cases. + + +#### dependentSchemas + +This keyword specifies subschemas that are evaluated if the instance +is an object and contains a certain property. + +This keyword's value MUST be an object. +Each value in the object MUST be a valid JSON Schema. + +If the object key is a property in the instance, the entire +instance must validate against the subschema. Its use is +dependent on the presence of the property. + +Omitting this keyword has the same behavior as an empty object. + + +#### propertyDependencies + +This keyword specifies subschemas that are evaluated if the instance is +an object and contains a certain property with a certain string value. + +This keyword's value MUST be an object. Each value in the object MUST be +an object whose values MUST be valid JSON Schemas. + +If the outer object key is a property in the instance and the inner +object key is equal to the value of that property, the entire instance +must validate against the schema. Its use is dependent on the presence +and value of the property. + +Omitting this keyword has the same behavior as an empty object. + + + + +## Keywords for Applying Subschemas to Child Instances + +Each of these keywords defines a rule for applying its +subschema(s) to child instances, specifically object +properties and array items, and combining their results. + +### Keywords for Applying Subschemas to Arrays + +#### prefixItems + +The value of "prefixItems" MUST be a non-empty array of valid JSON Schemas. + +Validation succeeds if each element of the instance validates +against the subschema at the same position, if any. This keyword +does not constrain the length of the array. Only array positions +present in both the keyword's value and the instance value are +affected by this keyword. + +This keyword produces an annotation value which is the largest +index to which this keyword applied a subschema. The value +MAY be a boolean true if a subschema was applied to every +index of the instance, such as is produced by the "items" keyword. +This annotation affects the behavior of "items" and "unevaluatedItems". + +Omitting this keyword has the same assertion behavior as +an empty array. + + +#### items {#items} + +The value of "items" MUST be a valid JSON Schema. + +This keyword applies its subschema to all instance elements +at indexes greater than the length of the "prefixItems" array +in the same schema object, as reported by the annotation result +of that "prefixItems" keyword. If no such annotation +result exists, "items" applies its subschema to all instance +array elements.[^CREF11] + +[^CREF11]: Note that the behavior of "items" without "prefixItems" is + identical to that of the schema form of "items" in prior drafts. + When "prefixItems" is present, the behavior of "items" is + identical to the former "additionalItems" keyword. + + +If the "items" subschema is applied to any +positions within the instance array, it produces an +annotation result of boolean true, indicating that all remaining array +elements have been evaluated against this keyword's subschema. +This annotation affects the behavior of "unevaluatedItems" in the +Unevaluated vocabulary. + +Omitting this keyword has the same assertion behavior as +an empty schema. + +Implementations MAY choose to implement or optimize this keyword +in another way that produces the same effect, such as by directly +checking for the presence and size of a "prefixItems" array. +Implementations that do not support annotation collection MUST do so. + + + +### Keywords for Applying Subschemas to Objects + +#### properties + +The value of "properties" MUST be an object. +Each value of this object MUST be a valid JSON Schema. + +Validation succeeds if, for each name that appears in both +the instance and as a name within this keyword's value, the child +instance for that name successfully validates against the +corresponding schema. + +The annotation result of this keyword is the set of instance +property names which are also present under this keyword. +This annotation affects the behavior of "additionalProperties" (in +this vocabulary) and "unevaluatedProperties" in the Unevaluated vocabulary. + +Omitting this keyword has the same assertion behavior as +an empty object. + + +#### patternProperties + +The value of "patternProperties" MUST be an object. Each property name +of this object SHOULD be a valid regular expression, according to the +ECMA-262 regular expression dialect. Each property value of this object +MUST be a valid JSON Schema. + +Validation succeeds if, for each instance name that matches any +regular expressions that appear as a property name in this keyword's value, +the child instance for that name successfully validates against each +schema that corresponds to a matching regular expression. Recall: regular +expressions are not implicitly anchored. + +The annotation result of this keyword is the set of instance +property names matched by at least one property under this keyword. +This annotation affects the behavior of "additionalProperties" (in this +vocabulary) and "unevaluatedProperties" (in the Unevaluated vocabulary). + +Omitting this keyword has the same assertion behavior as +an empty object. + + +#### additionalProperties {#additionalProperties} + +The value of "additionalProperties" MUST be a valid JSON Schema. + +The behavior of this keyword depends on the presence and +annotation results of "properties" and "patternProperties" +within the same schema object. +Validation with "additionalProperties" applies only to the child +values of instance names that do not appear in the annotation +results of either "properties" or "patternProperties". + +For all such properties, validation succeeds if the child instance +validates against the "additionalProperties" schema. + +The annotation result of this keyword is the set of instance +property names validated by this keyword's subschema. +This annotation affects the behavior of "unevaluatedProperties" +in the Unevaluated vocabulary. + +Omitting this keyword has the same assertion behavior as +an empty schema. + +Implementations MAY choose to implement or optimize this keyword +in another way that produces the same effect, such as by directly +checking the names in "properties" and the patterns in +"patternProperties" against the instance property set. +Implementations that do not support annotation collection MUST do so.[^CREF12] + +[^CREF12]: In defining this option, it seems there is the potential for + ambiguity in the output format. The ambiguity does not affect validation results, + but it does affect the resulting output format. + The ambiguity allows for multiple valid output results depending on whether annotations + are used or a solution that "produces the same effect" as draft-07. It is understood + that annotations from failing schemas are dropped. + See our + \[Decision Record](https://github.com/json-schema-org/json-schema-spec/tree/HEAD/adr/2022-04-08-cref-for-ambiguity-and-fix-later-gh-spec-issue-1172.md) + for further details. + + + +#### propertyNames + +The value of "propertyNames" MUST be a valid JSON Schema. + +If the instance is an object, this keyword validates if every property name +in +the instance validates against the provided schema. +Note the property name that the schema is testing will always be a string. + +Omitting this keyword has the same behavior as an empty schema. + + + +### Other Keywords for Applying Subschemas + +#### maxContains + +The value of this keyword MUST be a non-negative integer. + +This keyword modifies the behavior of "contains" within the same schema object, +as described below in the section for that keyword. + +Validation MUST always succeed against this keyword. +The value of this keyword is used as its annotation result. + + +#### minContains + +The value of this keyword MUST be a non-negative integer. + +This keyword modifies the behavior of "contains" within the same schema object, +as described below in the section for that keyword. + +Validation MUST always succeed against this keyword. +The value of this keyword is used as its annotation result. + +Per {{default-behaviors}}, +omitted keywords MUST NOT produce annotation results. However, as described +in the section for "contains", the absence of this keyword's annotation +causes "contains" to assume a minimum value of 1. + + +#### contains + +The value of this keyword MUST be a valid JSON Schema. + +This keyword applies its subschema to array elements or object property values. + +An instance is valid against "contains" if the number of elements or property +values that are valid against its subschema is with the inclusive range of +the minimum and (if any) maximum number of occurrences. + +The maximum number of occurrences is provided by the "maxContains" keyword +within the same schema object as "contains". If "maxContains" is absent, +the maximum number of occurrences MUST be unbounded. + +The minimum number of occurrences is provided by the "minContains" keyword +within the same schema object as "contains". If "minContains" is absent, +the minimum number of occurrences MUST be 1. + +Implementations MAY implement the dependency on "minContians" and +"maxContains" by inspecting their values rather than reading annotations +produced by those keywords. + +This keyword produces an annotation value which is an array of the +indexes or property names to which this keyword validates successfully +when applying its subschema, in ascending order. The value MAY be a +boolean "true" if the subschema validates successfully when applied to +every index or property value of the instance. The annotation MUST be +present if the instance array or object to which this keyword's schema +applies is empty. + +This annotation affects the behavior of "unevaluatedItems" in the +Unevaluated vocabulary. + +The subschema MUST be applied to every array element or object property +value even after the first match has been found, in order to collect +annotations for use by other keywords. This is to ensure that all possible +annotations are collected. + + + + + +# A Vocabulary for Unevaluated Locations + +The purpose of these keywords is to enable schema authors to apply +subschemas to array items or object properties that have not been +successfully evaluated against any dynamic-scope subschema of any +adjacent keywords. + +These instance items or properties may have been unsuccessfully evaluated +against one or more adjacent keyword subschemas, such as when an assertion +in a branch of an "anyOf" fails. Such failed evaluations are not considered +to contribute to whether or not the item or property has been evaluated. +Only successful evaluations are considered. + +If an item in an array or an object property is "successfully evaluated", +it +is logically considered to be valid in terms of the representation of the +object or array that's expected. For example if a subschema represents a +car, +which requires between 2-4 wheels, and the value of "wheels" is 6, the instance +object is not "evaluated" to be a car, and the "wheels" property is considered +"unevaluated (successfully as a known thing)", and does not retain any annotations. + +Recall that adjacent keywords are keywords within the same schema object, +and that the dynamic-scope subschemas include reference targets as well as +lexical subschemas. + +The behavior of these keywords depend on the annotation results of +adjacent keywords that apply to the instance location being validated. + +Meta-schemas that do not use "$vocabulary" SHOULD be considered to +require this vocabulary as if its IRI were present with a value of true. + +The current IRI for this vocabulary, known as the Unevaluated Applicator +vocabulary, is: +\. + +The current IRI for the corresponding meta-schema is: [](https://json-schema.org/draft/next/meta/unevaluated). + +## Keyword Independence + +Schema keywords typically operate independently, without +affecting each other's outcomes. However, the keywords in this +vocabulary are notable exceptions: + + +* "unevaluatedItems", whose behavior is defined in terms of annotations + from "prefixItems", "items", "contains", and itself + +* "unevaluatedProperties", whose behavior is defined in terms of + annotations from "properties", "patternProperties", + "additionalProperties", "contains", and itself + + +## unevaluatedItems {#unevaluatedItems} + +The value of "unevaluatedItems" MUST be a valid JSON Schema. + +The behavior of this keyword depends on the annotation results of +adjacent keywords that apply to the instance location being validated. +Specifically, the annotations from "prefixItems", "items", and "contains", +which can come from those keywords when they are adjacent to the +"unevaluatedItems" keyword. Those three annotations, as well as +"unevaluatedItems", can also result from any and all adjacent [in-place applicator](#in-place) keywords. +This includes but is not limited to the in-place applicators +defined in this document. + +If no relevant annotations are present, the "unevaluatedItems" +subschema MUST be applied to all locations in the array. +If a boolean true value is present from any of the relevant annotations, +"unevaluatedItems" MUST be ignored. Otherwise, the subschema +MUST be applied to any index greater than the largest annotation +value for "prefixItems", which does not appear in any annotation +value for "contains". + +This means that "prefixItems", "items", "contains", and all in-place +applicators MUST be evaluated before this keyword can be evaluated. +Authors of extension keywords MUST NOT define an in-place applicator +that would need to be evaluated after this keyword. + +If the "unevaluatedItems" subschema is applied to any +positions within the instance array, it produces an +annotation result of boolean true, analogous to the +behavior of "items". +This annotation affects the behavior of "unevaluatedItems" in parent schemas. + +Omitting this keyword has the same assertion behavior as +an empty schema. + + +## unevaluatedProperties {#unevaluatedProperties} + +The value of "unevaluatedProperties" MUST be a valid JSON Schema. + +The behavior of this keyword depends on the annotation results of +adjacent keywords that apply to the instance location being validated. +Specifically, the annotations from "properties", "patternProperties", +"contains", and "additionalProperties", which can come from those keywords +when +they are adjacent to the "unevaluatedProperties" keyword. Those +four annotations, as well as "unevaluatedProperties", can also +result from any and all adjacent [in-place applicator](#in-place) keywords. +This includes but is not limited to the in-place applicators +defined in this document. + +Validation with "unevaluatedProperties" applies only to the child +values of instance names that do not appear in the "properties", +"patternProperties", "additionalProperties", "contains", or +"unevaluatedProperties" annotation results that apply to the +instance location being validated. + +For all such properties, validation succeeds if the child instance +validates against the "unevaluatedProperties" schema. + +This means that "properties", "patternProperties", "additionalProperties", +"contains" and all in-place applicators MUST be evaluated before this keyword +can +be evaluated. Authors of extension keywords MUST NOT define an in-place +applicator that would need to be evaluated after this keyword. + +The annotation result of this keyword is the set of instance +property names validated by this keyword's subschema. +This annotation affects the behavior of "unevaluatedProperties" in parent +schemas. + +Omitting this keyword has the same assertion behavior as +an empty schema. + + + +# Output Formatting {#output} + +JSON Schema is defined to be platform-independent. As such, to increase +compatibility +across platforms, implementations SHOULD conform to a standard validation +output +format. This section describes the minimum requirements that consumers will +need to +properly interpret validation results. + +## Format + +JSON Schema output is defined using the JSON Schema data instance model as +described +in section 4.2.1. Implementations MAY deviate from this as supported by +their +specific languages and platforms, however it is RECOMMENDED that the output +be +convertible to the JSON format defined herein via serialization or other +means. + + +## Output Formats + +This specification defines three output formats. See the "Output Structure" +section for the requirements of each format. + + +Flag +: A boolean which simply indicates the overall validation result + with no further details. + +List +: Provides validation information in a flat list structure. + +Hierarchical +: Provides validation information in a hierarchical + structure that follows the evaluation paths generated while processing + the schema. + +An implementation MUST provide the "flag" format and SHOULD provide at least +one +of the "list" or "hierarchical" formats. Implementations SHOULD specify in +their documentation which formats they support. + + +## Minimum Information + +Beyond the simplistic "flag" output, additional information is useful to +aid in +debugging a schema or instance. Each sub-result SHOULD contain the information +contained within this section at a minimum. + +A single object that contains all of these components is considered an +output unit. + +Implementations MAY elect to provide additional information. + +### Evaluation path + +The evaluation path to the schema object that produced the output unit. +The value MUST be expressed as a JSON Pointer, and it MUST include any +by-reference applicators such as "$ref" or "$dynamicRef".[^CREF13] + +[^CREF13]: The schema may not actually have a value at the location indicated + by this pointer. It is provided as an indication of the traversal + path only. + + +~~~~ +/properties/width/$ref/allOf/1 +~~~~ + +Note that this pointer may not be resolvable by the normal JSON Pointer process +due to the inclusion of these by-reference applicator keywords. + +The JSON key for this information is "evaluationPath". + + +### Schema Location + +The absolute, dereferenced location of the schema object that produced +the output unit. The value MUST be expressed using the canonical IRI of +the +relevant schema resource plus a JSON Pointer fragment that indicates the +schema +object that produced the output. It MUST NOT include by-reference applicators +such as "$ref" or "$dynamicRef".[^CREF14] + +[^CREF14]: Note that "absolute" here is in the sense of "absolute filesystem path" + (meaning the complete location) rather than the "absolute-IRI" + terminology from RFC 3987 (meaning with scheme and without fragment). + Schema locations will have a fragment in order to identify the specific + schema object. + + +~~~~ +https://example.com/schemas/common#/$defs/allOf/1 + +~~~~ + +The JSON key for this information is "schemaLocation". + + +### Instance Location + +The location of the JSON value within the instance being validated. The +value MUST be expressed as a JSON Pointer. + +The JSON key for this information is "instanceLocation". + + +### Errors + +Any errors produced by the validation. This property MUST NOT +be included if the validation was successful. The value +for this property MUST be an object where the keys are the names of +keywords and the values are the error message produced by the +associated keyword. + +If the subschema itself is producing the error, that error MUST be +listed with an empty string key.[^CREF15] + +[^CREF15]: Although there may be other cases where a subschema can produce + an error, the most common case is the "false" schema. In + cases like these, there is no keyword that produces the error, + so there is nothing to use as a key. Thus the empty string + is used instead. + + +The specific wording for the message is not defined by this +specification. Implementations will need to provide this. + +The JSON key for this information is "errors". + + +### Annotations {#minimum-annotations} + +Any annotations produced by the evaluation. This property MUST NOT +be included if the validation result of the containing subschema was +unsuccessful. + +The value for this property MUST be an object where the +keys are the names of keywords and the values are the annotations +produced by the associated keyword. + +Each keyword defines its own annotation data type (e.g. "properties" +produces a list of keywords, whereas "title" produces a string). + +The JSON key for this information is "annotations". + + +### Dropped Annotations + +Any annotations produced and subsequently dropped by the evaluation +due to an unsuccessful validation result of the containing subschema. +This property MAY be included if the validation result of the containing +subschema was unsuccessful. It MUST NOT be included if the local +validation result of the containing subschema was successful. + +Implementations that wish to provide these annotations MUST NOT provide +them as their default behavior. These annotations MUST only be included +by explicitly configuring the implementation to do so. + +The value for this property MUST be an object where the +keys are the names of keywords and the values are the annotations +produced by the associated keyword. + +Each keyword defines its own annotation data type (e.g. "properties" +produces a list of keywords, whereas "title" produces a string). + +The JSON key for this information is "droppedAnnotations". + + +### Results from Subschemas + +Evaluation results generated by applying a subschema to the instance +or a child of the instance. +Keywords which have multiple subschemas (e.g. "anyOf") will generally +generate an output unit for each subschema. In order to accommodate +potentially multiple results, the value of this property MUST be an +array of output units, even if only a single output unit is produced. + +For "list", this property will appear only at the root output unit +and will hold all output units in a flat list. + +For "hierarchical", this property will contain results in a tree +structure where each output unit may itself have further nested results. + +The sequence of output units within this list is not specified and +MAY be determined by the implementation. Sets of output units are +considered equivalent if they contain the same units, in any order. + +The JSON key for these additional results is "details". + + + +## Output Structure + +The output MUST be an object containing a boolean property named "valid". +When +additional information about the result is required, the output MUST also +contain +"details" as described below. + + +valid +: a boolean value indicating the overall validation success or failure + +details +: the collection of results produced by subschemas + +For these examples, the following schema and instances will be used. + +~~~~ javascript +// schema +{ + "$schema": "https://json-schema.org/draft/next/schema", + "$id": "https://json-schema.org/schemas/example", + "type": "object", + "title": "root", + "properties": { + "foo": { + "allOf": [ + { "required": [ "unspecified-prop" ] }, + { + "type": "object", + "title": "foo-title", + "properties": { + "foo-prop": { + "const": 1, + "title": "foo-prop-title" + } + }, + "additionalProperties": { "type": "boolean" } + } + ] + }, + "bar": { + "$ref": "#/$defs/bar" + } + }, + "$defs": { + "bar": { + "type": "object", + "title": "bar-title", + "properties": { + "bar-prop": { + "type": "integer", + "minimum": 10, + "title": "bar-prop-title" + } + } + } + } +} + +// failing instance +{ + "foo": {"foo-prop": "not 1", "other-prop": false}, + "bar": {"bar-prop": 2} +} + +// passing instance +{ + "foo": { + "foo-prop": 1, + "unspecified-prop": true + }, + "bar": {"bar-prop": 20} +} +~~~~ + +The failing instance will produce the following errors: + + +* The value at "/foo" + evaluated at "/properties/foo/allOf/0" + by following the path "/properties/foo/allOf/0" + by the "required" keyword + is missing the property "unspecified-prop". + +* The value at "/foo/foo-prop" + evaluated at "/properties/foo/allOf/1/properties/foo-prop" + by following the path "/properties/foo/allOf/1/properties/foo-prop" + by the "const" keyword + is not the constant value 1. + +* The value at "/bar/bar-prop" + evaluated at "/$defs/bar/properties/bar-prop" + by following the path "/properties/bar/$ref/properties/bar-prop" + by the "type" keyword + is not a number. + +[^CREF16] + +[^CREF16]: "minimum" doesn't produce an error because it only operates on + instances that are numbers. + +[^CREF17] + +[^CREF17]: Note that the error message wording as depicted in the examples below is not a + requirement of this specification. Implementations SHO⁠ULD craft error messages + tailored for their audience or provide a templating mechanism that allows their + users to craft their own messages. + + +The passing instance will produce the following annotations: + + +* The keyword "title" + evaluated at "" + by following the path "" + will produce `"root"`. + +* The keyword "properties" + evaluated at "" + by following the path "" + will produce `["foo", "bar"]`. + +* The keyword "title" + evaluated at "/properties/foo" + by following the path "/properties/foo" + will produce `"foo-title"`. + +* The keyword "properties" + evaluated at "/properties/foo/allOf/1" + by following the path "/properties/foo/allOf/1" + will produce `["foo-prop"]`. + +* The keyword "additionalProperties" + evaluated at "/properties/foo/allOf/1" + by following the path "/properties/foo/allOf/1" + will produce `["unspecified-prop"]`. + +* The keyword "title" + evaluated at "/properties/foo/allOf/1/properties/foo-prop" + by following the path "/properties/foo/allOf/1/properties/foo-prop" + will produce `"foo-prop-title"`. + +* The keyword "title" + evaluated at "/$defs/bar" + by following the path "/properties/bar/$ref" + will produce `"bar-title"`. + +* The keyword "properties" + evaluated at "/$defs/bar" + by following the path "/properties/var/$ref" + will produce `["bar-prop"]`. + +* The keyword "title" + evaluated at "/$defs/bar/properties/bar-prop" + by following the path "/properties/bar/$ref/properties/bar-prop" + will produce `"bar-prop-title"`. + +### Flag + +In the simplest case, merely the boolean result for the "valid" valid property +needs to be fulfilled. For this format, all other information is explicitly +omitted. + +~~~~ json +{ + "valid": false +} +~~~~ + +Because no errors or annotations are returned with this format, it is +RECOMMENDED that implementations use short-circuiting logic to return +failure or success as soon as the outcome can be determined. For example, +if an "anyOf" keyword contains five subschemas, and the second one +passes, there is no need to check the other three. The logic can simply +return with success. + + +### List + +The "List" structure is a flat list of output units contained within a +root output unit. + +The root output unit contains "valid" for the overall result and "details" +for the list of specific results. All other information is explicitly +omitted from the root output unit. If the root schema produces errors or +annotations, then the output node for the root MUST be present within the +root output unit's "details" list with those errors or annotations. + +Output units which do not contain errors or annotations SHOULD be excluded +from this format, however implementations MAY choose to include them for +completeness. + +~~~~ javascript +// failing results +{ + "valid": false, + "details": [ + { + "valid": false, + "evaluationPath": "/properties/foo/allOf/0", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/0", + "instanceLocation": "/foo", + "errors": { + "required": "Required properties [\"unspecified-prop\"] were not present" + } + }, + { + "valid": false, + "evaluationPath": "/properties/foo/allOf/1/properties/foo-prop", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/1/properties/foo-prop", + "instanceLocation": "/foo/foo-prop", + "errors": { + "const": "Expected \"1\"" + } + }, + { + "valid": false, + "evaluationPath": "/properties/bar/$ref/properties/bar-prop", + "schemaLocation": "https://json-schema.org/schemas/example#/$defs/bar/properties/bar-prop", + "instanceLocation": "/bar/bar-prop", + "errors": { + "minimum": "2 is less than or equal to 10" + } + } + ] +} + +// passing results +{ + "valid": true, + "details": [ + { + "valid": true, + "evaluationPath": "", + "schemaLocation": "https://json-schema.org/schemas/example#", + "instanceLocation": "", + "annotations": { + "title": "root", + "properties": [ + "foo", + "bar" + ] + } + }, + { + "valid": true, + "evaluationPath": "/properties/foo/allOf/1", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/1", + "instanceLocation": "/foo", + "annotations": { + "title": "foo-title", + "properties": [ + "foo-prop" + ], + "additionalProperties": [ + "unspecified-prop" + ] + } + }, + { + "valid": true, + "evaluationPath": "/properties/bar/$ref", + "schemaLocation": "https://json-schema.org/schemas/example#/$defs/bar", + "instanceLocation": "/bar", + "annotations": { + "title": "bar-title", + "properties": [ + "bar-prop" + ] + } + }, + { + "valid": true, + "evaluationPath": "/properties/foo/allOf/1/properties/foo-prop", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/1/properties/foo-prop", + "instanceLocation": "/foo/foo-prop", + "annotations": { + "title": "foo-prop-title" + } + }, + { + "valid": true, + "evaluationPath": "/properties/bar/$ref/properties/bar-prop", + "schemaLocation": "https://json-schema.org/schemas/example#/$defs/bar/properties/bar-prop", + "instanceLocation": "/bar/bar-prop", + "annotations": { + "title": "bar-prop-title" + } + } + ] +} +~~~~ + + +### Hierarchical + +The "Hierarchical" structure is a tree structure that follows the +evaluation path during the validation process. Typically, it will +resemble the schema as if all referenced schemas were inlined in place +of their associated by-reference keywords. + +All output units are included in this format. + +The location properties of the root output unit MAY be omitted. + +~~~~ javascript +// failing results (errors) +{ + "valid": false, + "evaluationPath": "", + "schemaLocation": "https://json-schema.org/schemas/example#", + "instanceLocation": "", + "details": [ + { + "valid": false, + "evaluationPath": "/properties/foo", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo", + "instanceLocation": "/foo", + "details": [ + { + "valid": false, + "evaluationPath": "/properties/foo/allOf/0", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/0", + "instanceLocation": "/foo", + "errors": { + "required": "Required properties [\"unspecified-prop\"] were not present" + } + }, + { + "valid": false, + "evaluationPath": "/properties/foo/allOf/1", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/1", + "instanceLocation": "/foo", + "droppedAnnotations": { + "properties": [ "foo-prop" ], + "title": "foo-title" + }, + "details": [ + { + "valid": false, + "evaluationPath": "/properties/foo/allOf/1/properties/foo-prop", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/1/properties/foo-prop", + "instanceLocation": "/foo/foo-prop", + "errors": { + "const": "Expected \"1\"" + }, + "droppedAnnotations": { + "title": "foo-prop-title" + } + }, + { + "valid": true, + "evaluationPath": "/properties/foo/allOf/1/additionalProperties", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/1/additionalProperties", + "instanceLocation": "/foo/other-prop" + } + ] + } + ] + }, + { + "valid": false, + "evaluationPath": "/properties/bar", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/bar", + "instanceLocation": "/bar", + "details": [ + { + "valid": false, + "evaluationPath": "/properties/bar/$ref", + "schemaLocation": "https://json-schema.org/schemas/example#/$defs/bar", + "instanceLocation": "/bar", + "droppedAnnotations": { + "properties": [ "bar-prop" ], + "title": "bar-title" + }, + "details": [ + { + "valid": false, + "evaluationPath": "/properties/bar/$ref/properties/bar-prop", + "schemaLocation": "https://json-schema.org/schemas/example#/$defs/bar/properties/bar-prop", + "instanceLocation": "/bar/bar-prop", + "errors": { + "minimum": "2 is less than or equal to 10" + }, + "droppedAnnotations": { + "title": "bar-prop-title" + } + } + ] + } + ] + } + ] +} + +// passing results (annotations) +{ + "valid": true, + "evaluationPath": "", + "schemaLocation": "https://json-schema.org/schemas/example#", + "instanceLocation": "", + "annotations": { + "title": "root", + "properties": [ + "foo", + "bar" + ] + }, + "details": [ + { + "valid": true, + "evaluationPath": "/properties/foo", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo", + "instanceLocation": "/foo", + "details": [ + { + "valid": true, + "evaluationPath": "/properties/foo/allOf/0", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/0", + "instanceLocation": "/foo" + }, + { + "valid": true, + "evaluationPath": "/properties/foo/allOf/1", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/1", + "instanceLocation": "/foo", + "annotations": { + "title": "foo-title", + "properties": [ + "foo-prop" + ], + "additionalProperties": [ + "unspecified-prop" + ] + }, + "details": [ + { + "valid": true, + "evaluationPath": "/properties/foo/allOf/1/properties/foo-prop", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/1/properties/foo-prop", + "instanceLocation": "/foo/foo-prop", + "annotations": { + "title": "foo-prop-title" + } + }, + { + "valid": true, + "evaluationPath": "/properties/foo/allOf/1/additionalProperties", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/foo/allOf/1/additionalProperties", + "instanceLocation": "/foo/unspecified-prop" + } + ] + } + ] + }, + { + "valid": true, + "evaluationPath": "/properties/bar", + "schemaLocation": "https://json-schema.org/schemas/example#/properties/bar", + "instanceLocation": "/bar", + "details": [ + { + "valid": true, + "evaluationPath": "/properties/bar/$ref", + "schemaLocation": "https://json-schema.org/schemas/example#/$defs/bar", + "instanceLocation": "/bar", + "annotations": { + "title": "bar-title", + "properties": [ + "bar-prop" + ] + }, + "details": [ + { + "valid": true, + "evaluationPath": "/properties/bar/$ref/properties/bar-prop", + "schemaLocation": "https://json-schema.org/schemas/example#/$defs/bar/properties/bar-prop", + "instanceLocation": "/bar/bar-prop", + "annotations": { + "title": "bar-prop-title" + } + } + ] + } + ] + } + ] +} + +~~~~ + + +### Output validation schemas + +For convenience, JSON Schema has been provided to validate output generated +by implementations. Its IRI is: [](https://json-schema.org/draft/next/output/schema). + + + + +# Security Considerations {#security} + +Both schemas and instances are JSON values. As such, all security considerations +defined in [RFC 8259](#RFC8259) apply. + +Instances and schemas are both frequently written by untrusted third parties, +to be +deployed on public Internet servers. +Implementations should take care that the parsing and evaluating against +schemas +does not consume excessive system resources. +Implementations MUST NOT fall into an infinite loop. + +A malicious party could cause an implementation to repeatedly collect a copy +of a very large value as an annotation. Implementations SHOULD guard against +excessive consumption of system resources in such a scenario. + +Servers MUST ensure that malicious parties cannot change the functionality +of +existing schemas by uploading a schema with a pre-existing or very similar +"$id". + +Individual JSON Schema vocabularies are liable to also have their own security +considerations. Consult the respective specifications for more information. + +Schema authors should take care with "$comment" contents, as a malicious +implementation can display them to end-users in violation of a spec, or +fail to strip them if such behavior is expected. + +A malicious schema author could place executable code or other dangerous +material within a "$comment". Implementations MUST NOT parse or otherwise +take action based on "$comment" contents. + + +# IANA Considerations + +## application/schema+json + +The proposed MIME media type for JSON Schema is defined as follows: + + +Type name: +: application + +Subtype name: +: schema+json + +Required parameters: +: N/A + +Encoding considerations: +: Encoding considerations are + identical to those specified for the "application/json" + media type. See [JSON](#RFC8259). + +Security considerations: +: See {{security}} above. + +Interoperability considerations: +: See Sections {{ - - - - - - - - - - - - - -]> - - - - - - - - - - - JSON Schema: A Media Type for Describing JSON Documents - - -
- aaa@bzfx.net -
- - - -
- andrews_henry@yahoo.com -
- - - - Postman -
- ben@jsonschema.dev - https://jsonschema.dev -
- - - -
- gregsdennis@yahoo.com - https://github.com/gregsdennis -
- - - - Internet Engineering Task Force - JSON - Schema - Hyper Schema - Hypermedia - - - - JSON Schema defines the media type "application/schema+json", a JSON-based format - for describing the structure of JSON data. - JSON Schema asserts what a JSON document must look like, - ways to extract information from it, - and how to interact with it. - The "application/schema-instance+json" media type provides additional - feature-rich integration with "application/schema+json" beyond what can be offered - for "application/json" documents. - - - - - The issues list for this draft can be found at - . - - - For additional information, see . - - - To provide feedback, use this issue tracker, the communication methods listed on the - homepage, or email the document editors. - - - - - -
- - JSON Schema is a JSON media type for defining the structure of JSON data. JSON Schema - is intended to define validation, documentation, hyperlink navigation, and interaction - control of JSON data. - - - This specification defines JSON Schema core terminology and mechanisms, including - pointing to another JSON Schema by reference, - dereferencing a JSON Schema reference, - specifying the dialect being used, - specifying a dialect's vocabulary requirements, - and defining the expected output. - - - Other specifications define the vocabularies that perform assertions about validation, - linking, annotation, navigation, and interaction. - -
- -
- - - - The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", - "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be - interpreted as described in RFC 2119. - - - - The terms "JSON", "JSON text", "JSON value", "member", "element", "object", "array", - "number", "string", "boolean", "true", "false", and "null" in this document are to - be interpreted as defined in RFC 8259. - -
- -
- - This document proposes a new media type "application/schema+json" to identify a JSON - Schema for describing JSON data. - It also proposes a further optional media type, "application/schema-instance+json", - to provide additional integration features. - JSON Schemas are themselves JSON documents. - This, and related specifications, define keywords allowing authors to describe JSON - data in several ways. - - - JSON Schema uses keywords to assert constraints on JSON instances or annotate those - instances with additional information. Additional keywords are used to apply - assertions and annotations to more complex JSON data structures, or based on - some sort of condition. - - - To facilitate re-use, keywords can be organized into vocabularies. A vocabulary - consists of a list of keywords, together with their syntax and semantics. - A dialect is defined as a set of vocabularies and their required support - identified in a meta-schema. - - - JSON Schema can be extended either by defining additional vocabularies, - or less formally by defining additional keywords outside of any vocabulary. - Unrecognized individual keywords simply have their values collected as annotations, - while the behavior with respect to an unrecognized vocabulary can be controlled - when declaring which vocabularies are in use. - - - This document defines a core vocabulary that MUST be supported by any - implementation, and cannot be disabled. Its keywords are each prefixed - with a "$" character to emphasize their required nature. This vocabulary - is essential to the functioning of the "application/schema+json" media - type, and is used to bootstrap the loading of other vocabularies. - - - Additionally, this document defines a RECOMMENDED vocabulary of keywords - for applying subschemas conditionally, and for applying subschemas to - the contents of objects and arrays. Either this vocabulary or one very - much like it is required to write schemas for non-trivial JSON instances, - whether those schemas are intended for assertion validation, annotation, - or both. While not part of the required core vocabulary, for maximum - interoperability this additional vocabulary is included in this document - and its use is strongly encouraged. - - - Further vocabularies for purposes such as structural validation or - hypermedia annotation are defined in other documents. These other - documents each define a dialect collecting the standard sets of - vocabularies needed to write schemas for that document's purpose. - -
- -
- -
- - A JSON document is an information resource (series of octets) described by the - application/json media type. - - - In JSON Schema, the terms "JSON document", "JSON text", and "JSON value" are - interchangeable because of the data model it defines in . - - - JSON Schema is only defined over JSON documents. However, any document or memory - structure that can be parsed into or processed according to the JSON Schema data - model can be interpreted against a JSON Schema, including media types like - CBOR. - -
- -
- - A JSON document to which a schema is applied is known as an "instance". - - - JSON Schema is defined over "application/json" or compatible documents, - including media types with the "+json" structured syntax suffix. - - - Among these, this specification defines the "application/schema-instance+json" - media type which defines handling for fragments in the IRI. - - -
- - JSON Schema interprets documents according to a data model. A JSON value - interpreted according to this data model is called an "instance". - - - An instance has one of six primitive types, and a range of possible values - depending on the type: - -
-
null
A JSON "null" value
-
boolean
A "true" or "false" value, from the JSON "true" or "false" value
-
object
An unordered set of properties mapping a string to an instance, from the JSON "object" value
-
array
An ordered list of instances, from the JSON "array" value
-
number
An arbitrary-precision, base-10 decimal number value, from the JSON "number" value
-
string
A string of Unicode code points, from the JSON "string" value
-
- - - Whitespace and formatting concerns, including different lexical - representations of numbers that are equal within the data model, are thus - outside the scope of JSON Schema. JSON Schema - vocabularies that wish - to work with such differences in lexical representations SHOULD define - keywords to precisely interpret formatted strings within the data model - rather than relying on having the original JSON representation Unicode - characters available. - - - Since an object cannot have two properties with the same key, behavior for a - JSON document that tries to define two properties with - the same key in a single object is undefined. - - - Note that JSON Schema vocabularies are free to define their own extended - type system. This should not be confused with the core data model types - defined here. As an example, "integer" is a reasonable type for a - vocabulary to define as a value for a keyword, but the data model - makes no distinction between integers and other numbers. - -
- -
- - Two JSON instances are said to be equal if and only if they are of the same type - and have the same value according to the data model. Specifically, this means: - -
    -
  • both are null; or
    • -
  • both are true; or
    • -
  • both are false; or
    • -
  • both are strings, and are the same codepoint-for-codepoint; or
    • -
  • both are numbers, and have the same mathematical value; or
    • -
  • both are arrays, and have an equal value item-for-item; or
    • -
  • both are objects, and each property in one has exactly one property with - a key equal to the other's, and that other property has an equal - value.
    • -
- - - Implied in this definition is that arrays must be the same length, - objects must have the same number of members, - properties in objects are unordered, - there is no way to define multiple properties with the same key, - and mere formatting differences (indentation, placement of commas, trailing - zeros) are insignificant. - -
- -
- - It is possible to use JSON Schema with a superset of the JSON Schema data model, - where an instance may be outside any of the six JSON data types. - - - In this case, annotations still apply; but most validation keywords will not be useful, - as they will always pass or always fail. - - - A custom vocabulary may define support for a superset of the core data model. - The schema itself may only be expressible in this superset; - for example, to make use of the "const" keyword. - -
-
- -
- - A JSON Schema document, or simply a schema, is a JSON document used to describe - an instance. - A schema can itself be interpreted as an instance, but SHOULD always be given - the media type "application/schema+json" rather than - "application/schema-instance+json". The "application/schema+json" media - type is defined to offer a superset of the - fragment identifier syntax and semantics provided by - "application/schema-instance+json". - - - A JSON Schema MUST be an object or a boolean. - -
- - Object properties that are applied to the instance are called keywords, - or schema keywords. Broadly speaking, keywords fall into one - of five categories: - -
-
identifiers
-
- control schema identification through setting a IRI - for the schema and/or changing how the base IRI is determined -
-
assertions
-
- produce a boolean result when applied to an instance -
-
annotations
-
- attach information to an instance for application use -
-
applicators
-
- apply one or more subschemas to a particular location - in the instance, and combine or modify their results -
-
reserved locations
-
- do not directly affect results, but reserve a place - for a specific purpose to ensure interoperability -
-
- - Keywords may fall into multiple categories, although applicators - SHOULD only produce assertion results based on their subschemas' - results. They should not define additional constraints independent - of their subschemas. - - - Keywords which are properties within the same schema object are referred to as adjacent keywords. - - - Extension keywords, meaning those defined outside of this document - and its companions, are free to define other behaviors as well. - - - A JSON Schema MAY contain properties which are not schema keywords or are not recognized as schema keywords. - The behavior of such keywords is governed by . - - - An empty schema is a JSON Schema with no properties. - -
-
- - The boolean schema values "true" and "false" are trivial schemas that - always produce themselves as assertion results, regardless of the - instance value. They never produce annotation results. - - - These boolean schemas exist to clarify schema author intent and - facilitate schema processing optimizations. They behave identically - to the following schema objects (where "not" is part of the - subschema application vocabulary defined in this document). - -
-
true
-
- Always passes validation, as if the empty schema {} -
- -
false
-
- Always fails validation, as if the schema { "not": {} } -
-
- - While the empty schema object is unambiguous, there are many - possible equivalents to the "false" schema. Using the boolean - values ensures that the intent is clear to both human readers - and implementations. - -
-
- - A schema vocabulary, or simply a vocabulary, is a set of keywords, - their syntax, and their semantics. A vocabulary is generally organized - around a particular purpose. Different uses of JSON Schema, such - as validation, hypermedia, or user interface generation, will - involve different sets of vocabularies. - - - Vocabularies are the primary unit of re-use in JSON Schema, as schema - authors can indicate what vocabularies are required or optional in - order to process the schema. Since vocabularies are identified by IRIs - in the meta-schema, generic implementations can load extensions to support - previously unknown vocabularies. While keywords can be supported outside - of any vocabulary, there is no analogous mechanism to indicate individual - keyword usage. - - - A schema vocabulary can be defined by anything from an informal description - to a standards proposal, depending on the audience and interoperability - expectations. In particular, in order to facilitate vocabulary use within - non-public organizations, a vocabulary specification need not be published - outside of its scope of use. - -
-
- - A schema that itself describes a schema is called a meta-schema. - Meta-schemas are used to validate JSON Schemas and specify which vocabularies - they are using. - - - Typically, a meta-schema will specify a set of vocabularies, and validate - schemas that conform to the syntax of those vocabularies. However, meta-schemas - and vocabularies are separate in order to allow meta-schemas to validate - schema conformance more strictly or more loosely than the vocabularies' - specifications call for. Meta-schemas may also describe and validate - additional keywords that are not part of a formal vocabulary. - -
-
- - A JSON Schema resource is a schema which is - canonically identified by an - absolute IRI. Schema resources MAY - also be identified by IRIs, including IRIs with fragments, - if the resulting secondary resource (as defined by - section 3.5 of RFC 3986) is identical - to the primary resource. This can occur with the empty fragment, - or when one schema resource is embedded in another. Any such IRIs - with fragments are considered to be non-canonical. - - - The root schema is the schema that comprises the entire JSON document - in question. The root schema is always a schema resource, where the - IRI is determined as described in . - - Note that documents that embed schemas in another format will not - have a root schema resource in this sense. Exactly how such usages - fit with the JSON Schema document and resource concepts will be - clarified in a future draft. - - - - Some keywords take schemas themselves, allowing JSON Schemas to be nested: - - - - In this example document, the schema titled "array item" is a subschema, - and the schema titled "root" is the root schema. - - - As with the root schema, a subschema is either an object or a boolean. - - - As discussed in , a JSON Schema document - can contain multiple JSON Schema resources. When used without qualification, - the term "root schema" refers to the document's root schema. In some - cases, resource root schemas are discussed. A resource's root schema - is its top-level schema object, which would also be a document root schema - if the resource were to be extracted to a standalone JSON Schema document. - - - Whether multiple schema resources are embedded or linked with a reference, - they are processed in the same way, with the same available behaviors. - -
-
- -
- -
- - In accordance with section 3.1 of RFC 6839, - the syntax and semantics of fragment identifiers specified for - any +json media type SHOULD be as specified for "application/json". - (At publication of this document, there is no fragment identification - syntax defined for "application/json".) - - - Additionally, the "application/schema+json" media type supports two - fragment identifier structures: plain names and JSON Pointers. - The "application/schema-instance+json" media type supports one - fragment identifier structure: JSON Pointers. - - - The use of JSON Pointers as IRI fragment identifiers is described in - RFC 6901. - For "application/schema+json", which supports two fragment identifier syntaxes, - fragment identifiers matching the JSON Pointer syntax, including the empty string, - MUST be interpreted as JSON Pointer fragment identifiers. - - - Per the W3C's - best practices for fragment identifiers, - plain name fragment identifiers in "application/schema+json" are reserved for referencing - locally named schemas. - - - Plain name fragments MUST start with a letter ([A-Za-z]) or underscore ("_"), - followed by any number of letters, digits ([0-9]), hyphens ("-"), - underscores ("_"), and periods ("."). This matches the US-ASCII part of XML's - NCName production, which allows for compatibility - with the recommended plain name syntax for - XML-based media types. - - - All fragment identifiers that do - not match the JSON Pointer syntax MUST be interpreted as - plain name fragment identifiers. - - - Defining and referencing a plain name fragment identifier within an - "application/schema+json" document are specified - in the "$anchor" keyword section. - -
- -
- -
- - An instance may be any valid JSON value as defined by JSON. - JSON Schema imposes no restrictions on type: JSON Schema can describe any JSON - value, including, for example, null. - -
- -
- - JSON Schema is programming language agnostic, and supports the full range of - values described in the data model. - Be aware, however, that some languages and JSON parsers may not be able to - represent in memory the full range of values describable by JSON. - -
- -
- - Some programming languages and parsers use different internal representations - for floating point numbers than they do for integers. - - - For consistency, integer JSON numbers SHOULD NOT be encoded with a fractional - part. - -
- -
- - Keywords MAY use regular expressions to express constraints, or constrain - the instance value to be a regular expression. - These regular expressions SHOULD be valid according to the regular expression - dialect described in ECMA-262, section 21.2.1. - - - Unless otherwise specified by a keyword, regular expressions MUST NOT be - considered to be implicitly anchored at either end. All regular expression - keywords in this specification and its companion documents are un-anchored. - - - Regular expressions SHOULD be built with the "u" flag (or equivalent) to provide - Unicode support, or processed in such a way which provides Unicode support as - defined by ECMA-262. - - - Furthermore, given the high disparity in regular expression constructs support, - schema authors SHOULD limit themselves to the following regular expression - tokens: - -
    -
  • individual Unicode characters, as defined by the JSON specification;
    • -
  • simple character classes ([abc]), range character classes ([a-z]);
    • -
  • complemented character classes ([^abc], [^a-z]);
    • -
  • simple quantifiers: "+" (one or more), "*" (zero or more), "?" (zero or - one), and their lazy versions ("+?", "*?", "??");
    • -
  • range quantifiers: "{x}" (exactly x occurrences), "{x,y}" (at least x, at - most y, occurrences), {x,} (x occurrences or more), and their lazy - versions;
    • -
  • the beginning-of-input ("^") and end-of-input ("$") anchors;
    • -
  • simple grouping ("(...)") and alternation ("|").
    • -
- - - Finally, implementations MUST NOT take regular expressions to be - anchored, neither at the beginning nor at the end. This means, for instance, - the pattern "es" matches "expression". - -
- -
- - Additional schema keywords and schema vocabularies MAY be defined - by any entity. Save for explicit agreement, schema authors SHALL NOT - expect these additional keywords and vocabularies to be supported by - implementations that do not explicitly document such support. - - - Implementations MAY provide the ability to register or load handlers - for vocabularies that they do not support directly. The exact mechanism - for registering and implementing such handlers is implementation-dependent. - - -
- - The values of keywords which begin with "x-" MUST be collected as annotations. - - - Keywords which begin with "x-" symbol MUST NOT affect evaluation - of a schema in any way other than annotation collection. - - - Consequently, the "x-" prefix is reserved for this purpose, and - extension vocabularies MUST NOT define any keywords which begin - with this prefix. - -
- -
- - Implementations SHOULD treat keywords they do not recognize, or that - they recognize but do not support, as annotations, where the value of - the keyword is the value of the annotation. Whether an implementation - collects these annotations or not, they MUST otherwise ignore the keywords. - -
-
- -
- -
- - JSON Schema keywords fall into several general behavior categories. - Assertions validate that an instance satisfies constraints, producing - a boolean result. Annotations attach information that applications - may use in any way they see fit. - Applicators apply subschemas to parts of the instance and combine - their results. - - - Extension keywords SHOULD stay within these categories, keeping in mind - that annotations in particular are extremely flexible. Complex behavior - is usually better delegated to applications on the basis of annotation - data than implemented directly as schema keywords. However, extension - keywords MAY define other behaviors for specialized purposes. - - - Evaluating an instance against a schema involves processing all of the - keywords in the schema against the appropriate locations within the instance. - Typically, applicator keywords are processed until a schema object with no - applicators (and therefore no subschemas) is reached. The appropriate - location in the instance is evaluated against the assertion and - annotation keywords in the schema object. The interactions of those - keyword results to produce the schema object results are governed by - , while the - relationship of subschema results to the results of the applicator - keyword that applied them is described by . - - - Evaluation of a parent schema object can complete once all of its - subschemas have been evaluated, although in some circumstances evaluation - may be short-circuited due to assertion results. When annotations are - being collected, some assertion result short-circuiting is not possible - due to the need to examine all subschemas for annotation collection, including - those that cannot further change the assertion result. - -
- - While most JSON Schema keywords can be evaluated on their own, - or at most need to take into account the values or results of - adjacent keywords in the same schema object, a few have more - complex behavior. - - - The lexical scope of a keyword is determined by the nested JSON - data structure of objects and arrays. The largest such scope - is an entire schema document. The smallest scope is a single - schema object with no subschemas. - - - Keywords MAY be defined with a partial value, such as a IRI-reference, - which must be resolved against another value, such as another - IRI-reference or a full IRI, which is found through the lexical - structure of the JSON document. The "$id", "$ref", and - "$dynamicRef" core keywords, and the "base" JSON Hyper-Schema - keyword, are examples of this sort of behavior. - - - Note that some keywords, such as "$schema", apply to the lexical - scope of the entire schema resource, and therefore MUST only - appear in a schema resource's root schema. - - - Other keywords may take into account the dynamic scope that - exists during the evaluation of a schema, typically together - with an instance document. - The outermost dynamic scope is the schema object at - which processing begins, even if it is not a schema resource root. - The path from this root schema to any particular keyword (that - includes any "$ref" and "$dynamicRef" keywords that may have - been resolved) is considered the keyword's "evaluation path." - - - Lexical and dynamic scopes align until a reference keyword - is encountered. While following the reference keyword moves processing - from one lexical scope into a different one, from the perspective - of dynamic scope, following a reference is no different from descending - into a subschema present as a value. A keyword on the far side of - that reference that resolves information through the dynamic scope - will consider the originating side of the reference to be their - dynamic parent, rather than examining the local lexically enclosing parent. - - - The concept of dynamic scope is primarily used with "$dynamicRef" and - "$dynamicAnchor", and should be considered an advanced feature - and used with caution when defining additional keywords. It also appears - when reporting errors and collected annotations, as it may be possible - to revisit the same lexical scope repeatedly with different dynamic - scopes. In such cases, it is important to inform the user of the - evaluation path that produced the error or annotation. - -
-
- - Keyword behavior MAY be defined in terms of the annotation results - of subschemas and/or adjacent keywords - (keywords within the same schema object) and their subschemas. - Such keywords MUST NOT result in a circular dependency. - Keywords MAY modify their behavior based on the presence or absence - of another keyword in the same - schema object. - -
-
- - A missing keyword MUST NOT produce a false assertion result, MUST - NOT produce annotation results, and MUST NOT cause any other schema - to be evaluated as part of its own behavioral definition. - However, given that missing keywords do not contribute annotations, - the lack of annotation results may indirectly change the behavior - of other keywords. - - - In some cases, the missing keyword assertion behavior of a keyword is - identical to that produced by a certain value, and keyword definitions - SHOULD note such values where known. However, even if the value which - produces the default behavior would produce annotation results if - present, the default behavior still MUST NOT result in annotations. - - - Because annotation collection can add significant cost in terms of both - computation and memory, implementations MAY opt out of this feature. - Keywords that are specified in terms of collected annotations SHOULD - describe reasonable alternate approaches when appropriate. - This approach is demonstrated by the - "" and - "" keywords in this - document. - - - Note that when no such alternate approach is possible for a keyword, - implementations that do not support annotation collections will not - be able to support those keywords or vocabularies that contain them. - -
-
- - Identifiers define IRIs for a schema, or affect how such IRIs are - resolved in references, or both. - The Core vocabulary defined in this document defines several - identifying keywords, most notably "$id". - - - Canonical schema IRIs MUST NOT change while processing an instance, but - keywords that affect IRI-reference resolution MAY have behavior that - is only fully determined at runtime. - - - While custom identifier keywords are possible, vocabulary designers should - take care not to disrupt the functioning of core keywords. For example, - the "$dynamicAnchor" keyword in this specification limits its IRI resolution - effects to the matching "$dynamicRef" keyword, leaving the behavior - of "$ref" undisturbed. - -
-
- - Applicators allow for building more complex schemas than can be accomplished - with a single schema object. Evaluation of an instance against a - schema document begins by applying - the root schema to the complete instance - document. From there, keywords known as applicators are used to determine - which additional schemas are applied. Such schemas may be applied in-place - to the current location, or to a child location. - - - The schemas to be applied may be present as subschemas comprising all or - part of the keyword's value. Alternatively, an applicator may refer to - a schema elsewhere in the same schema document, or in a different one. - The mechanism for identifying such referenced schemas is defined by the - keyword. - - - Applicator keywords also define how subschema or referenced schema - boolean assertion - results are modified and/or combined to produce the boolean result - of the applicator. Applicators may apply any boolean logic operation - to the assertion results of subschemas, but MUST NOT introduce new - assertion conditions of their own. - - - Annotation results from subschemas - are preserved in accordance with so that applications - can decide how to interpret multiple values. Applicator keywords - do not play a direct role in this preservation. - -
- - As noted in , an applicator keyword may - refer to a schema to be applied, rather than including it as a - subschema in the applicator's value. In such situations, the - schema being applied is known as the referenced schema, while - the schema containing the applicator keyword is the referencing schema. - - - While root schemas and subschemas are static concepts based on a - schema's position within a schema document, referenced and referencing - schemas are dynamic. Different pairs of schemas may find themselves - in various referenced and referencing arrangements during the evaluation - of an instance against a schema. - - - For some by-reference applicators, such as - "$ref", the referenced schema can be determined - by static analysis of the schema document's lexical scope. Others, - such as "$dynamicRef" (with "$dynamicAnchor"), may make use of dynamic - scoping, and therefore only be resolvable in the process of evaluating - the schema with an instance. - -
-
- -
- - JSON Schema can be used to assert constraints on a JSON document, which - either passes or fails the assertions. This approach can be used to validate - conformance with the constraints, or document what is needed to satisfy them. - - - JSON Schema implementations produce a single boolean result when evaluating - an instance against schema assertions. - - - An instance can only fail an assertion that is present in the schema. - - -
- - Most assertions only constrain values within a certain - primitive type. When the type of the instance is not of the type - targeted by the keyword, the instance is considered to conform - to the assertion. - - - For example, the "maxLength" keyword from the companion - validation vocabulary: - will only restrict certain strings - (that are too long) from being valid. If the instance is a number, - boolean, null, array, or object, then it is valid against this assertion. - - - This behavior allows keywords to be used more easily with instances - that can be of multiple primitive types. The companion validation - vocabulary also includes a "type" keyword which can independently - restrict the instance to one or more primitive types. This allows - for a concise expression of use cases such as a function that might - return either a string of a certain length or a null value: - - - - If "maxLength" also restricted the instance type to be a string, - then this would be substantially more cumbersome to express because - the example as written would not actually allow null values. - Each keyword is evaluated separately unless explicitly specified - otherwise, so if "maxLength" restricted the instance to strings, - then including "null" in "type" would not have any useful effect. - -
-
- -
- - JSON Schema can annotate an instance with information, whenever the instance - validates against the schema object containing the annotation, and all of its - parent schema objects. The information can be a simple value, or can be - calculated based on the instance contents. - - - Annotations are attached to specific locations in an instance. - Since many subschemas can be applied to any single - location, applications may need to decide how to handle differing - annotation values being attached to the same instance location by - the same schema keyword in different schema objects. - - - Unlike assertion results, annotation data can take a wide variety of forms, - which are provided to applications to use as they see fit. JSON Schema - implementations are not expected to make use of the collected information - on behalf of applications. - - - Unless otherwise specified, the value of an annotation keyword - is the keyword's value. However, other behaviors are possible. - For example, JSON Hyper-Schema's - "links" keyword is a complex annotation that produces a value based - in part on the instance data. - - - While "short-circuit" evaluation is possible for assertions, collecting - annotations requires examining all schemas that apply to an instance - location, even if they cannot change the overall assertion result. - The only exception is that subschemas of a schema object that has - failed validation MAY be skipped, as annotations are not retained - for failing schemas. - - -
- - Annotations are collected by keywords that explicitly define - annotation-collecting behavior. Note that boolean schemas cannot - produce annotations as they do not make use of keywords. - - - A collected annotation MUST include the following information: - -
    -
  • - The name of the keyword that produces the annotation -
    • -
  • - The instance location to which it is attached, as a JSON Pointer -
    • -
  • - The evaluation path, indicating how reference keywords - such as "$ref" were followed to reach the absolute schema location. -
    • -
  • - The absolute schema location of the attaching keyword, as a IRI. - This MAY be omitted if it is the same as the evaluation path - from above. -
    • -
  • - The attached value(s) -
    • -
-
- - Applications MAY make decisions on which of multiple annotation values - to use based on the schema location that contributed the value. - This is intended to allow flexible usage. Collecting the schema location - facilitates such usage. - - - For example, consider this schema, which uses annotations and assertions from - the Validation specification: - - - Note that some lines are wrapped for clarity. - - - - In this example, both Feature A and Feature B make use of the re-usable - "enabledToggle" schema. That schema uses the "title", "description", - and "default" annotations. Therefore the application has to decide how - to handle the additional "default" value for Feature A, and the additional - "description" value for Feature B. - - - The application programmer and the schema author need to agree on the - usage. For this example, let's assume that they agree that the most - specific "default" value will be used, and any additional, more generic - "default" values will be silently ignored. Let's also assume that they - agree that all "description" text is to be used, starting with the most - generic, and ending with the most specific. This requires the schema - author to write descriptions that work when combined in this way. - - - The application can use the evaluation path to determine which - values are which. The values in the feature's immediate "enabled" - property schema are more specific, while the values under the re-usable - schema that is referenced to with "$ref" are more generic. The evaluation - path will show whether each value was found by crossing a - "$ref" or not. - - - Feature A will therefore use a default value of true, while Feature B - will use the generic default value of null. Feature A will only - have the generic description from the "enabledToggle" schema, while - Feature B will use that description, and also append its locally - defined description that explains how to interpret a null value. - - - Note that there are other reasonable approaches that a different application - might take. For example, an application may consider the presence of - two different values for "default" to be an error, regardless of their - schema locations. - -
-
- - Schema objects that produce a false assertion result MUST NOT - produce any annotation results, whether from their own keywords - or from keywords in subschemas. - - - Note that the overall schema results may still include annotations - collected from other schema locations. Given this schema: - - - - Against the instance "This is a string", the - title annotation "Integer Value" is discarded because the type assertion - in that schema object fails. The title annotation "String Value" - is kept, as the instance passes the string type assertions. - -
-
-
-
- - A fourth category of keywords simply reserve a location to hold re-usable - components or data of interest to schema authors that is not suitable - for re-use. These keywords do not affect validation or annotation results. - Their purpose in the core vocabulary is to ensure that locations are - available for certain purposes and will not be redefined by extension - keywords. - - - While these keywords do not directly affect results, as explained in - unrecognized - extension keywords that reserve locations for re-usable schemas may have - undesirable interactions with references in certain circumstances. - -
-
- - While none of the vocabularies defined as part of this or the associated documents - define a keyword which may target and/or load instance data, it is possible that - other vocabularies may wish to do so. - - - Keywords MAY be defined to use JSON Pointers or Relative JSON Pointers to examine - parts of an instance outside the current evaluation location. - - - Keywords that allow adjusting the location using a Relative JSON Pointer SHOULD - default to using the current location if a default is desireable. - -
-
-
- - Keywords declared in this section, which all begin with "$", make up - the JSON Schema Core vocabulary. These keywords are either required in - order to process any schema or meta-schema, including those split across - multiple documents, or exist to reserve keywords for purposes that - require guaranteed interoperability. - - - The Core vocabulary MUST be considered mandatory at all times, in order - to bootstrap the processing of further vocabularies. Meta-schemas - that use the "$vocabulary" keyword - to declare the vocabularies in use MUST explicitly list the Core vocabulary, - which MUST have a value of true indicating that it is required. - - - The behavior of a false value for this vocabulary (and only this - vocabulary) is undefined, as is the behavior when "$vocabulary" - is present but the Core vocabulary is not included. However, it - is RECOMMENDED that implementations detect these cases and raise - an error when they occur. It is not meaningful to declare that - a meta-schema optionally uses Core. - - - Meta-schemas that do not use "$vocabulary" MUST be considered to - require the Core vocabulary as if its IRI were present with a value of true. - - - The current IRI for the Core vocabulary is: - <https://json-schema.org/draft/next/vocab/core>. - - - The current IRI for the corresponding meta-schema is: - . - - - The "$" prefix is reserved for use by the Core vocabulary. - Vocabulary extensions MUST NOT define new keywords that begin with "$". - - -
- - Two concepts, meta-schemas and vocabularies, are used to inform an implementation - how to interpret a schema. Every schema has a meta-schema, which can be declared - using the "$schema" keyword. - - - The meta-schema serves two purposes: - -
-
Declaring the vocabularies in use
-
- The "$vocabulary" keyword, when it appears in a meta-schema, declares - which vocabularies are available to be used in schemas that refer - to that meta-schema. Vocabularies define keyword semantics, - as well as their general syntax. -
-
Describing valid schema syntax
-
- A schema MUST successfully validate against its meta-schema, which - constrains the syntax of the available keywords. The syntax described - is expected to be compatible with the vocabularies declared; while - it is possible to describe an incompatible syntax, such a meta-schema - would be unlikely to be useful. -
-
- - Meta-schemas are separate from vocabularies to allow for - vocabularies to be combined in different ways, and for meta-schema authors - to impose additional constraints such as forbidding certain keywords, or - performing unusually strict syntactical validation, as might be done - during a development and testing cycle. Each vocabulary typically identifies - a meta-schema consisting only of the vocabulary's keywords. - - - Meta-schema authoring is an advanced usage of JSON Schema, so the design of - meta-schema features emphasizes flexibility over simplicity. - -
- - The "$schema" keyword is both used as a JSON Schema dialect identifier and - as the identifier of a resource which is itself a JSON Schema, which describes the - set of valid schemas written for this particular dialect. - - - The value of this keyword MUST be a IRI - (containing a scheme) and this IRI MUST be normalized. - The current schema MUST be valid against the meta-schema identified by this IRI. - - - If this IRI identifies a retrievable resource, that resource SHOULD be of - media type "application/schema+json". - - - The "$schema" keyword SHOULD be used in the document root schema object, - and MAY be used in the root schema objects of embedded schema resources. - It MUST NOT appear in non-resource root schema objects. If absent from - the document root schema, the resulting behavior is implementation-defined, - but MUST fall within the following options: -
    -
  • Refuse to process the schema, as with unsupported required - vocabularies
    • -
  • Assume a specific, documented meta-schema
    • -
  • Document the process by which it examines the schema and determines - which of a specific set of meta-schemas to assume
    • -
- - - Values for this property are defined elsewhere in this and other documents, - and by other parties. - -
-
- - The "$vocabulary" keyword is used in meta-schemas to identify the - vocabularies available for use in schemas described by that meta-schema, - and whether each vocabulary is required or optional. Together, this - information forms a dialect. - - - The value of this keyword MUST be an object. The property names in the - object MUST be IRIs (containing a scheme) and each IRI MUST be normalized. - Each IRI that appears as a property name identifies a specific set of - keywords and their semantics. - - - The IRI MAY be a URL, but the nature of the retrievable resource is - currently undefined, and reserved for future use. Vocabulary authors - MAY use the URL of the vocabulary specification, in a human-readable - media type such as text/html or text/plain, as the vocabulary IRI. - - Vocabulary documents may be added in forthcoming drafts. - For now, identifying the keyword set is deemed sufficient as that, - along with meta-schema validation, is how the current "vocabularies" - work today. Any future vocabulary document format will be specified - as a JSON document, so using text/html or other non-JSON formats - in the meantime will not produce any future ambiguity. - - - - The values of the object properties MUST be booleans. - If the value is true, then the vocabulary MUST be considered to be required. - If the value is false, then the vocabulary MUST be considered to be optional. - -
- - A schema is said to use a dialect and its constituent vocabularies if it is - associated with a meta-schema defining the dialect with "$vocabulary", - either through "$schema", through appropriately defined media type parameters - or link relation types, or through documented default implementation-defined - behavior in the absence of an explicit meta-schema. If a meta-schema - does not contain "$vocabulary", the set of vocabularies in use is determined - according to . - - - Any vocabulary in use by a schema and understood by the implementation - MUST be processed in a manner consistent with the semantic definitions - contained within the vocabulary, regardless of whether that vocabulary - is required or optional. - - - Any vocabulary that is not present in "$vocabulary" MUST NOT be made - available for use in schemas described by that meta-schema, except for - the core vocabulary as specified by the introduction to - . - - - Implementations that do not support a vocabulary required by a schema - MUST refuse to process that schema. - - - Implementations that do not support a vocabulary that is optionally used - by a schema SHOULD proceed with processing the schema. The keywords will - be considered to be unrecognized keywords as addressed by - . Note that since - the recommended behavior for such keywords is to collect them as - annotations, vocabularies consisting only of annotations will have - the same behavior when used optionally whether the implementation - supports them or not. This allows annotation-only vocabularies to - be supported without custom code, even in implementations that do - not support providing custom code for extension vocabularies. - -
-
- - The "$vocabulary" keyword SHOULD be used in the root schema of any schema - resource intended for use as a meta-schema. It MUST NOT appear in subschemas. - - - The "$vocabulary" keyword MUST be ignored in schema resources that - are not being processed as a meta-schema. This allows validating - a meta-schema M against its own meta-schema M' without requiring - the validator to understand the vocabularies declared by M. - -
-
- - Keywords from different vocabularies, as well as non-vocabulary - extension keywords, can have identical names. These are not - considered to be the same keyword from the perspective of - enabling or disabling them through "$vocabulary". - - - In particular the keywords defined in this specification and its - companion documents MUST be considered to be vocabulary keywords, - with availability governed by "$vocabulary" even in implementations - that do not support any extension vocabularies. - - - Guidance regarding vocabularies with identically-named keywords is provided - in . - -
-
- - If "$vocabulary" is absent, an implementation MAY determine - behavior based on the meta-schema if it is recognized from the - IRI value of the referring schema's "$schema" keyword. - This is how behavior (such as Hyper-Schema usage) has been - recognized prior to the existence of vocabularies. - - - If the meta-schema, as referenced by the schema, is not recognized, - or is missing, then the behavior is implementation-defined. - If the implementation - proceeds with processing the schema, it MUST assume the use of the - core vocabulary. If the implementation is built for a specific purpose, - then it SHOULD assume the use of all of the most relevant vocabularies - for that purpose. - - - For example, an implementation that is a validator - SHOULD assume the use of all vocabularies in this - specification and the companion Validation specification. - -
-
- - Note that the processing restrictions on "$vocabulary" mean that - meta-schemas that reference other meta-schemas using "$ref" or - similar keywords do not automatically inherit the vocabulary - declarations of those other meta-schemas. All such declarations - must be repeated in the root of each schema document intended - for use as a meta-schema. This is demonstrated in - the example meta-schema. - - This requirement allows implementations to find all vocabulary - requirement information in a single place for each meta-schema. - As schema extensibility means that there are endless potential - ways to combine more fine-grained meta-schemas by reference, - requiring implementations to anticipate all possibilities and - search for vocabularies in referenced meta-schemas would - be overly burdensome. - - -
-
-
- - Updated vocabulary and meta-schema IRIs MAY be published between - specification drafts in order to correct errors. Implementations - SHOULD consider IRIs dated after this specification draft and - before the next to indicate the same syntax and semantics - as those listed here. - -
-
- -
- - To differentiate between schemas in a vast ecosystem, schemas are - identified by IRI, and can embed references - to other schemas by specifying their IRI. - - - Several keywords can accept a relative IRI-reference, - or a value used to construct a relative IRI-reference. For these keywords, - it is necessary to establish a base IRI in order to resolve the reference. - - -
- - The "$id" keyword identifies a schema resource with its - canonical IRI. - - - Note that this IRI is an identifier and not necessarily a network locator. - In the case of a network-addressable URL, a schema need not be downloadable - from its canonical IRI. - - - If present, the value for this keyword MUST be a string, and MUST represent a - valid IRI-reference. This IRI-reference - SHOULD be normalized, and MUST resolve to an - absolute-IRI (without a fragment). - - - The resulting absolute-IRI serves as the base IRI for relative IRI-references - in keywords within the schema resource, in accordance with - RFC 3987 section 6.5 and - RFC 3986 section 5.1.1 regarding base IRIs - embedded in content. - - - The presence of "$id" in a subschema indicates that the subschema constitutes - a distinct schema resource within a single schema document. Furthermore, - in accordance with RFC 3987 section 6.5 and - RFC 3986 section 5.1.2 regarding - encapsulating entities, if an "$id" in a subschema is a relative - IRI-reference, the base IRI for resolving that reference is the IRI of - the parent schema resource. Note that an "$id" consisting of an empty IRI or - of the empty fragment only will result in the embedded resource having - the same IRI as the encapsulating resource, which SHOULD be considered - an error per . - - - If no parent schema object explicitly identifies itself as a resource - with "$id", the base IRI is that of the entire document, as established - by the steps given in the previous section. - -
- - The root schema of a JSON Schema document SHOULD contain an "$id" keyword - with an absolute-IRI (containing a scheme, - but no fragment). - -
-
-
- - Using JSON Pointer fragments requires knowledge of the structure of the schema. - When writing schema documents with the intention to provide re-usable - schemas, it may be preferable to use a plain name fragment that is not tied to - any particular structural location. This allows a subschema to be relocated - without requiring JSON Pointer references to be updated. - - - The "$anchor" and "$dynamicAnchor" keywords are used to specify such - fragments. They are identifier keywords that can only be used to create - plain name fragments, rather than absolute IRIs as seen with "$id". - - - The base IRI to which the resulting fragment is appended is the canonical - IRI of the schema resource containing the "$anchor" or "$dynamicAnchor" - in question. As discussed in the previous section, this is either the - nearest "$id" in the same or parent schema object, - or the base IRI for the document as determined according to - RFC 3987 and - RFC 3986. - - - Separately from the usual usage of IRIs, "$dynamicAnchor" - indicates that the fragment is an extension point when used with - the "$dynamicRef" keyword. This low-level, advanced feature - makes it easier to extend recursive schemas such as the meta-schemas, - without imposing any particular semantics on that extension. - See the section on "$dynamicRef" - for details. - - - In most cases, the normal fragment behavior both suffices and - is more intuitive. Therefore it is RECOMMENDED that "$anchor" - be used to create plain name fragments unless there is a clear - need for "$dynamicAnchor". - - - If present, the value of these keywords MUST be a string and MUST conform - to the plain name fragment identifier syntax defined in - . - - Note that the anchor string does not include the "#" character, - as it is not a IRI-reference. An "$anchor": "foo" becomes the - fragment "#foo" when used in a IRI. See below for full examples. - - -
- -
- - A schema MAY (and likely will) have multiple IRIs, but there is no way - for an IRI to identify more than one schema. When multiple schemas - attempt to identify as the same IRI through the use of "$id", "$anchor", - "$dynamicAnchor", or any other mechanism, implementations SHOULD raise - an error condition. Otherwise the result is undefined, and even if - documented will not be interoperable. - -
- -
- - Several keywords can be used to reference a schema which is to be applied to the - current instance location. "$ref" and "$dynamicRef" are applicator - keywords, applying the referenced schema to the instance. - - - As the values of "$ref" and "$dynamicRef" are IRI References, this allows - the possibility to externalise or divide a schema across multiple files, - and provides the ability to validate recursive structures through - self-reference. - - - The resolved IRI produced by these keywords is not necessarily a network - locator, only an identifier. A schema need not be downloadable from the - address if it is a network-addressable URL, and implementations SHOULD NOT - assume they should perform a network operation when they encounter - a network-addressable IRI. - - -
- - The "$ref" keyword is an applicator that is used to reference a statically - identified schema. Its results are the results of the referenced schema. - - Note that this definition of how the results are determined means that - other keywords can appear alongside of "$ref" in the same schema object. - - - - The value of the "$ref" keyword MUST be a string which is a IRI-Reference. - Resolved against the current IRI base, it produces the IRI of the schema - to apply. This resolution is safe to perform on schema load, as the - process of evaluating an instance cannot change how the reference resolves. - -
- -
- - The "$dynamicRef" keyword is an applicator that allows for deferring the - full resolution until runtime, at which point it is resolved each time it is - encountered while evaluating an instance. - - - Together with "$dynamicAnchor", "$dynamicRef" implements a cooperative - extension mechanism that is primarily useful with recursive schemas - (schemas that reference themselves). The extension point is defined with - "$dynamicAnchor" and only exhibits runtime dynamic behavior when referenced - with "$dynamicRef". - - - The value of the "$dynamicRef" property MUST be a string which is a - IRI-Reference that contains a valid plain name - fragment. Resolved against the current IRI base, it indicates - the schema resource used as the starting point for runtime resolution. - This initial resolution is safe to perform on schema load. - - - The schema to apply is the outermost schema resource in the - dynamic scope that defines a - "$dynamicAnchor" that matches the plain name fragment in the initially - resolved IRI. - - - For a full example using these keyword, see . - - The difference between the hyper-schema meta-schema in pre-2019 - drafts and an this draft dramatically demonstrates the utility - of these keywords. - - -
- -
- -
- - The "$defs" keyword reserves a location for schema - authors to inline re-usable JSON Schemas into a more general schema. - The keyword does not directly affect the validation result. - - - This keyword's value MUST be an object. - Each member value of this object MUST be a valid JSON Schema. - - - As an example, here is a schema describing an array of positive - integers, where the positive integer constraint is a subschema in - "$defs": - - -
-
- -
- - This keyword reserves a location for comments from schema authors - to readers or maintainers of the schema. - - - The value of this keyword MUST be a string. Implementations MUST NOT present this - string to end users. Tools for editing schemas SHOULD support displaying and - editing this keyword. The value of this keyword MAY be used in debug or error - output which is intended for developers making use of schemas. - - - Schema vocabularies SHOULD allow "$comment" within any object containing - vocabulary keywords. Implementations MAY assume "$comment" is allowed - unless the vocabulary specifically forbids it. Vocabularies MUST NOT - specify any effect of "$comment" beyond what is described in this - specification. - - - Tools that translate other media types or programming languages - to and from application/schema+json MAY choose to convert that media type or - programming language's native comments to or from "$comment" values. - The behavior of such translation when both native comments and "$comment" - properties are present is implementation-dependent. - - - Implementations MAY strip "$comment" values at any point during processing. - In particular, this allows for shortening schemas when the size of deployed - schemas is a concern. - - - Implementations MUST NOT take any other action based on the presence, absence, - or contents of "$comment" properties. In particular, the value of "$comment" - MUST NOT be collected as an annotation result. - -
-
- -
- - -
-
- - RFC 3987 Section 6.5 and - RFC 3986 Section 5.1 defines how to determine the - default base IRI of a document. - - - Informatively, the initial base IRI of a schema is the IRI at which it was - found, whether that was a network location, a local filesystem, or any other - situation identifiable by a IRI of any known scheme. - - - If a schema document defines no explicit base IRI with "$id" - (embedded in content), the base IRI is that determined per - RFC 3987 Section 6.5 and - RFC 3986 section 5. - - - If no source is known, or no IRI scheme is known for the source, a suitable - implementation-specific default IRI MAY be used as described in - RFC 3987 Section 6.5 and - RFC 3986 Section 5.1.4. It is RECOMMENDED - that implementations document any default base IRI that they assume. - - - If a schema object is embedded in a document of another media type, then - the initial base IRI is determined according to the rules of that - media type. - - - Unless the "$id" keyword described in an earlier section is present in the - root schema, this base IRI SHOULD be considered the canonical IRI of the - schema document's root schema resource. - -
- -
- - The use of IRIs to identify remote schemas does not necessarily mean anything is downloaded, - but instead JSON Schema implementations SHOULD understand ahead of time which schemas they will be using, - and the IRIs that identify them. - - - When schemas are downloaded, - for example by a generic user-agent that does not know until runtime which schemas to download, - see Usage for Hypermedia. - - - Implementations SHOULD be able to associate arbitrary IRIs with an arbitrary - schema and/or automatically associate a schema's "$id"-given IRI, depending - on the trust that the validator has in the schema. Such IRIs and schemas - can be supplied to an implementation prior to processing instances, or may - be noted within a schema document as it is processed, producing associations - as shown in . - -
- -
- - Implementations MUST recognize a schema as a meta-schema if it - is being examined because it was identified as such by another - schema's "$schema" keyword. This means that a single schema - document might sometimes be considered a regular schema, and - other times be considered a meta-schema. - - - In the case of examining a schema which is its own meta-schema, - when an implementation begins processing it as a regular schema, - it is processed under those rules. However, when loaded a second - time as a result of checking its own "$schema" value, it is treated - as a meta-schema. So the same document is processed both ways in - the course of one session. - - - Implementations MAY allow a schema to be explicitly passed as a meta-schema, - for implementation-specific purposes, such as pre-loading a commonly - used meta-schema and checking its vocabulary support requirements - up front. Meta-schema authors MUST NOT expect such features to be - interoperable across implementations. - -
-
- -
- - Schemas can be identified by any IRI that has been given to them, including - a JSON Pointer or their IRI given directly by "$id". In all cases, - dereferencing a "$ref" reference involves first resolving its value as a - IRI reference against the current base IRI per - RFC 3986. - - - If the resulting IRI identifies a schema within the current document, or - within another schema document that has been made available to the implementation, - then that schema SHOULD be used automatically. - - - For example, consider this schema: - - - - - When an implementation encounters the <#/$defs/single> schema, - it resolves the "$anchor" value as a fragment name against the current - base IRI to form <https://example.net/root.json#item>. - - - When an implementation then looks inside the <#/items> schema, it - encounters the <#item> reference, and resolves this to - <https://example.net/root.json#item>, which it has seen defined in - this same document and can therefore use automatically. - - - When an implementation encounters the reference to "other.json", it resolves - this to <https://example.net/other.json>, which is not defined in this - document. If a schema with that identifier has otherwise been supplied to - the implementation, it can also be used automatically. - - What should implementations do when the referenced schema is not known? - Are there circumstances in which automatic network dereferencing is - allowed? A same origin policy? A user-configurable option? In the - case of an evolving API described by Hyper-Schema, it is expected that - new schemas will be added to the system dynamically, so placing an - absolute requirement of pre-loading schema documents is not feasible. - - - -
- - Since JSON Pointer IRI fragments are constructed based on the structure - of the schema document, an embedded schema resource and its subschemas - can be identified by JSON Pointer fragments relative to either its own - canonical IRI, or relative to any containing resource's IRI. - - - Conceptually, a set of linked schema resources should behave - identically whether each resource is a separate document connected with - schema references, or is structured as - a single document with one or more schema resources embedded as - subschemas. - - - Since IRIs involving JSON Pointer fragments relative to the parent - schema resource's IRI cease to be valid when the embedded schema - is moved to a separate document and referenced, applications and schemas - SHOULD NOT use such IRIs to identify embedded schema resources or - locations within them. - - - Consider the following schema document that contains another - schema resource embedded within it: - - - - The IRI "https://example.com/foo#/items" points to the "items" schema, - which is an embedded resource. The canonical IRI of that schema - resource, however, is "https://example.com/bar". - - - For the "additionalProperties" schema within that embedded resource, - the IRI "https://example.com/foo#/items/additionalProperties" points - to the correct object, but that object's IRI relative to its resource's - canonical IRI is "https://example.com/bar#/additionalProperties". - - - Now consider the following two schema resources linked by reference - using a IRI value for "$ref": - - - - - Here we see that "https://example.com/bar#/additionalProperties", - using a JSON Pointer fragment appended to the canonical IRI of - the "bar" schema resource, is still valid, while - "https://example.com/foo#/items/additionalProperties", which relied - on a JSON Pointer fragment appended to the canonical IRI of the - "foo" schema resource, no longer resolves to anything. - - - Note also that "https://example.com/foo#/items" is valid in both - arrangements, but resolves to a different value. This IRI ends up - functioning similarly to a retrieval IRI for a resource. While this IRI - is valid, it is more robust to use the "$id" of the embedded or referenced - resource unless it is specifically desired to identify the object containing - the "$ref" in the second (non-embedded) arrangement. - - - An implementation MAY choose not to support addressing schema resource - contents by IRIs using a base other than the resource's canonical IRI, - plus a JSON Pointer fragment relative to that base. Therefore, schema - authors SHOULD NOT rely on such IRIs, as using them may reduce interoperability. - - This is to avoid requiring implementations to keep track of a whole - stack of possible base IRIs and JSON Pointer fragments for each, - given that all but one will be fragile if the schema resources - are reorganized. Some - have argued that this is easy so there is - no point in forbidding it, while others have argued that it complicates - schema identification and should be forbidden. Feedback on this - topic is encouraged. - After some discussion, we feel that we need to remove the use of - "canonical" in favour of talking about JSON Pointers which reference - across schema resource boundaries as undefined or even forbidden behavior - (https://github.com/json-schema-org/json-schema-spec/issues/937, - https://github.com/json-schema-org/json-schema-spec/issues/1183) - - - - Further examples of such non-canonical IRI construction, as well as - the appropriate canonical IRI-based fragments to use instead, - are provided in . - -
-
- -
- - A Compound Schema Document is defined as a JSON document (sometimes called a "bundled" schema) - which has multiple embedded JSON Schema Resources bundled into the same document to - ease transportation. - - - Each embedded Schema Resource MUST be treated as an individual Schema Resource, following standard - schema loading and processing requirements, including determining vocabulary support. - -
- - The bundling process for creating a Compound Schema Document is defined as taking - references (such as "$ref") to an external Schema Resource and embedding the referenced - Schema Resources within the referring document. Bundling SHOULD be done in such a way that - all IRIs (used for referencing) in the base document and any referenced/embedded - documents do not require altering. - - - Each embedded JSON Schema Resource MUST identify itself with a IRI using the "$id" keyword, - and SHOULD make use of the "$schema" keyword to identify the dialect it is using, in the root of the - schema resource. It is RECOMMENDED that the IRI identifier value of "$id" be an Absolute IRI. - - - When the Schema Resource referenced by a by-reference applicator is bundled, it is RECOMMENDED that - the Schema Resource be located as a value of a "$defs" object at the containing schema's root. - The key of the "$defs" for the now embedded Schema Resource MAY be the "$id" of the bundled schema - or some other form of application defined unique identifer (such as a UUID). This key is not - intended to be referenced in JSON Schema, but may be used by an application to aid the - bundling process. - - - A Schema Resource MAY be embedded in a location other than "$defs" where the location is defined - as a schema value. - - - A Bundled Schema Resource MUST NOT be bundled by replacing the schema object from which it was - referenced, or by wrapping the Schema Resource in other applicator keywords. - - - In order to produce identical output, references in the containing schema document to the - previously external Schema Resources MUST NOT be changed, and now resolve to a schema using the - "$id" of an embedded Schema Resource. Such identical output includes validation evaluation and IRIs - or paths used in resulting annotations or errors. - - - While the bundling process will often be the main method for creating a Compound Schema Document, - it is also possible and expected that some will be created by hand, potentially without individual - Schema Resources existing on their own previously. - -
-
- - When multiple schema resources are present in a single document, - schema resources which do not define with which dialect they should be processed - MUST be processed with the same dialect as the enclosing resource. - - - Since any schema that can be referenced can also be embedded, embedded schema resources MAY - specify different processing dialects using the "$schema" values from their enclosing resource. - -
-
- - Given that a Compound Schema Document may have embedded resources which identify as using different - dialects, these documents SHOULD NOT be validated by applying a meta-schema - to the Compound Schema Document as an instance. It is RECOMMENDED that an alternate - validation process be provided in order to validate Schema Documents. Each Schema Resource - SHOULD be separately validated against its associated meta-schema. - - If you know a schema is what's being validated, you can identify if the schemas - is a Compound Schema Document or not, by way of use of "$id", which identifies an - embedded resource when used not at the document's root. - - - - A Compound Schema Document in which all embedded resources identify as using the same - dialect, or in which "$schema" is omitted and therefore defaults to that of the enclosing resource, - MAY be validated by applying the appropriate meta-schema. - -
-
- -
-
- - A schema MUST NOT be run into an infinite loop against an instance. For - example, if two schemas "#alice" and "#bob" both have an "allOf" property - that refers to the other, a naive validator might get stuck in an infinite - recursive loop trying to validate the instance. Schemas SHOULD NOT make - use of infinite recursive nesting like this; the behavior is undefined. - -
- -
- - Subschema objects (or booleans) are recognized by their use with known - applicator keywords or with location-reserving keywords such as - "$defs" that take one or more subschemas - as a value. These keywords may be "$defs" and the standard applicators - from this document, or extension keywords from a known vocabulary, or - implementation-specific custom keywords. - - - Multi-level structures of unknown keywords are capable of introducing - nested subschemas, which would be subject to the processing rules for - "$id". Therefore, having a reference target in such an unrecognized - structure cannot be reliably implemented, and the resulting behavior - is undefined. Similarly, a reference target under a known keyword, - for which the value is known not to be a schema, results in undefined - behavior in order to avoid burdening implementations with the need - to detect such targets. - - These scenarios are analogous to fetching a schema over HTTP - but receiving a response with a Content-Type other than - application/schema+json. An implementation can certainly - try to interpret it as a schema, but the origin server - offered no guarantee that it actually is any such thing. - Therefore, interpreting it as such has security implications - and may produce unpredictable results. - - - - Note that single-level custom keywords with identical syntax and - semantics to "$defs" do not allow for any intervening "$id" keywords, - and therefore will behave correctly under implementations that attempt - to use any reference target as a schema. However, this behavior is - implementation-specific and MUST NOT be relied upon for interoperability. - -
-
- -
- -
- - - JSON has been adopted widely by HTTP servers for automated APIs and robots. This - section describes how to enhance processing of JSON documents in a more RESTful - manner when used with protocols that support media types and - Web linking. - - -
- - It is RECOMMENDED that instances described by a schema provide a link to - a downloadable JSON Schema using the link relation "describedby", as defined by - Linked Data Protocol 1.0, section 8.1. - - - - In HTTP, such links can be attached to any response using the - Link header. An example of such a header would be: - - - ; rel="describedby" -]]> - -
- -
- - When used for hypermedia systems over a network, - HTTP is frequently the protocol of choice for - distributing schemas. Misbehaving clients can pose problems for server - maintainers if they pull a schema over the network more frequently than - necessary, when it's instead possible to cache a schema for a long period of - time. - - - HTTP servers SHOULD set long-lived caching headers on JSON Schemas. - HTTP clients SHOULD observe caching headers and not re-request documents within - their freshness period. - Distributed systems SHOULD make use of a shared cache and/or caching proxy. - - - Clients SHOULD set or prepend a User-Agent header specific to the JSON Schema - implementation or software product. Since symbols are listed in decreasing order - of significance, the JSON Schema library name/version should precede the more - generic HTTP library name (if any). For example: - - - - Clients SHOULD be able to make requests with a "From" header so that server - operators can contact the owner of a potentially misbehaving script. - -
- -
- -
- -
- -
- - This section defines a vocabulary of applicator keywords that - are RECOMMENDED for use as the basis of other vocabularies. - - - Meta-schemas that do not use "$vocabulary" SHOULD be considered to - require this vocabulary as if its IRI were present with a value of true. - - - The current IRI for this vocabulary, known as the Applicator vocabulary, is: - <https://json-schema.org/draft/next/vocab/applicator>. - - - The current IRI for the corresponding meta-schema is: - . - -
- - Schema keywords typically operate independently, without - affecting each other's outcomes. - - - For schema author convenience, there are some exceptions among the - keywords in this vocabulary: - -
    -
  • - "additionalProperties", whose behavior is defined in terms of - "properties" and "patternProperties" -
    • -
  • - "items", whose behavior is defined in terms of "prefixItems" -
    • -
  • - "contains", whose behavior is affected by the presence and value of - "minContains" -
    • -
-
- -
- - These keywords apply subschemas to the same location in the instance - as the parent schema is being applied. They allow combining - or modifying the subschema results in various ways. - - - - Subschemas of these keywords evaluate the instance completely independently - such that the results of one such subschema MUST NOT impact the results of sibling - subschemas. Therefore subschemas may be applied in - any order. - - -
- - These keywords correspond to logical operators for combining or modifying - the boolean assertion results of the subschemas. They have no direct - impact on annotation collection, although they enable the same annotation - keyword to be applied to an instance location with different values. - Annotation keywords define their own rules for combining such values. - -
- - This keyword's value MUST be a non-empty array. - Each item of the array MUST be a valid JSON Schema. - - - An instance validates successfully against this keyword if it validates - successfully against all schemas defined by this keyword's value. - -
- -
- - This keyword's value MUST be a non-empty array. - Each item of the array MUST be a valid JSON Schema. - - - An instance validates successfully against this keyword if it validates - successfully against at least one schema defined by this keyword's value. - Note that when annotations are being collected, all subschemas MUST - be examined so that annotations are collected from each subschema - that validates successfully. - -
- -
- - This keyword's value MUST be a non-empty array. - Each item of the array MUST be a valid JSON Schema. - - - An instance validates successfully against this keyword if it validates - successfully against exactly one schema defined by this keyword's value. - -
- -
- - This keyword's value MUST be a valid JSON Schema. - - - An instance is valid against this keyword if it fails to validate - successfully against the schema defined by this keyword. - -
-
- -
- - Three of these keywords work together to implement conditional - application of a subschema based on the outcome of another subschema. - The fourth is a shortcut for a specific conditional case. - - - "if", "then", and "else" MUST NOT interact with each other across - subschema boundaries. In other words, an "if" in one - branch of an "allOf" MUST NOT have an impact on a "then" - or "else" in another branch. - - - There is no default behavior for "if", "then", or "else" - when they are not present. In particular, they MUST NOT - be treated as if present with an empty schema, and when - "if" is not present, both "then" and "else" MUST be - entirely ignored. - -
- - This keyword's value MUST be a valid JSON Schema. - - - This validation outcome of this keyword's subschema - has no direct effect on the overall validation - result. Rather, it controls which of the "then" - or "else" keywords are evaluated. - - - Instances that successfully validate against this - keyword's subschema MUST also be valid against - the subschema value of the "then" keyword, if - present. - - - Instances that fail to validate against this - keyword's subschema MUST also be valid against - the subschema value of the "else" keyword, if - present. - - - If annotations - are being collected, they are collected from this - keyword's subschema in the usual way, including when - the keyword is present without either "then" or "else". - -
-
- - This keyword's value MUST be a valid JSON Schema. - - - When "if" is present, and the instance successfully - validates against its subschema, then validation - succeeds against this keyword if the instance also - successfully validates against this keyword's subschema. - - - This keyword has no effect when "if" is absent, or - when the instance fails to validate against its - subschema. Implementations MUST NOT evaluate - the instance against this keyword, for either validation - or annotation collection purposes, in such cases. - -
-
- - This keyword's value MUST be a valid JSON Schema. - - - When "if" is present, and the instance fails to - validate against its subschema, then validation - succeeds against this keyword if the instance - successfully validates against this keyword's subschema. - - - This keyword has no effect when "if" is absent, or - when the instance successfully validates against its - subschema. Implementations MUST NOT evaluate - the instance against this keyword, for either validation - or annotation collection purposes, in such cases. - -
-
- - This keyword specifies subschemas that are evaluated if the instance - is an object and contains a certain property. - - - This keyword's value MUST be an object. - Each value in the object MUST be a valid JSON Schema. - - - If the object key is a property in the instance, the entire - instance must validate against the subschema. Its use is - dependent on the presence of the property. - - - Omitting this keyword has the same behavior as an empty object. - -
-
- - This keyword specifies subschemas that are evaluated if the instance is - an object and contains a certain property with a certain string value. - - - This keyword's value MUST be an object. Each value in the object MUST be - an object whose values MUST be valid JSON Schemas. - - - If the outer object key is a property in the instance and the inner - object key is equal to the value of that property, the entire instance - must validate against the schema. Its use is dependent on the presence - and value of the property. - - - Omitting this keyword has the same behavior as an empty object. - -
-
-
-
- - Each of these keywords defines a rule for applying its - subschema(s) to child instances, specifically object - properties and array items, and combining their results. - -
-
- - The value of "prefixItems" MUST be a non-empty array of valid JSON Schemas. - - - Validation succeeds if each element of the instance validates - against the subschema at the same position, if any. This keyword - does not constrain the length of the array. Only array positions - present in both the keyword's value and the instance value are - affected by this keyword. - - - This keyword produces an annotation value which is the largest - index to which this keyword applied a subschema. The value - MAY be a boolean true if a subschema was applied to every - index of the instance, such as is produced by the "items" keyword. - This annotation affects the behavior of "items" and "unevaluatedItems". - - - Omitting this keyword has the same assertion behavior as - an empty array. - -
- -
- - The value of "items" MUST be a valid JSON Schema. - - - This keyword applies its subschema to all instance elements - at indexes greater than the length of the "prefixItems" array - in the same schema object, as reported by the annotation result - of that "prefixItems" keyword. If no such annotation - result exists, "items" applies its subschema to all instance - array elements. - - Note that the behavior of "items" without "prefixItems" is - identical to that of the schema form of "items" in prior drafts. - When "prefixItems" is present, the behavior of "items" is - identical to the former "additionalItems" keyword. - - - - If the "items" subschema is applied to any - positions within the instance array, it produces an - annotation result of boolean true, indicating that all remaining array - elements have been evaluated against this keyword's subschema. - This annotation affects the behavior of "unevaluatedItems" in the - Unevaluated vocabulary. - - - Omitting this keyword has the same assertion behavior as - an empty schema. - - - Implementations MAY choose to implement or optimize this keyword - in another way that produces the same effect, such as by directly - checking for the presence and size of a "prefixItems" array. - Implementations that do not support annotation collection MUST do so. - -
-
- -
-
- - The value of "properties" MUST be an object. - Each value of this object MUST be a valid JSON Schema. - - - Validation succeeds if, for each name that appears in both - the instance and as a name within this keyword's value, the child - instance for that name successfully validates against the - corresponding schema. - - - The annotation result of this keyword is the set of instance - property names which are also present under this keyword. - This annotation affects the behavior of "additionalProperties" (in - this vocabulary) and "unevaluatedProperties" in the Unevaluated vocabulary. - - - Omitting this keyword has the same assertion behavior as - an empty object. - -
- -
- - The value of "patternProperties" MUST be an object. Each property name - of this object SHOULD be a valid regular expression, according to the - ECMA-262 regular expression dialect. Each property value of this object - MUST be a valid JSON Schema. - - - Validation succeeds if, for each instance name that matches any - regular expressions that appear as a property name in this keyword's value, - the child instance for that name successfully validates against each - schema that corresponds to a matching regular expression. Recall: regular - expressions are not implicitly anchored. - - - The annotation result of this keyword is the set of instance - property names matched by at least one property under this keyword. - This annotation affects the behavior of "additionalProperties" (in this - vocabulary) and "unevaluatedProperties" (in the Unevaluated vocabulary). - - - Omitting this keyword has the same assertion behavior as - an empty object. - -
- -
- - The value of "additionalProperties" MUST be a valid JSON Schema. - - - The behavior of this keyword depends on the presence and - annotation results of "properties" and "patternProperties" - within the same schema object. - Validation with "additionalProperties" applies only to the child - values of instance names that do not appear in the annotation - results of either "properties" or "patternProperties". - - - For all such properties, validation succeeds if the child instance - validates against the "additionalProperties" schema. - - - The annotation result of this keyword is the set of instance - property names validated by this keyword's subschema. - This annotation affects the behavior of "unevaluatedProperties" - in the Unevaluated vocabulary. - - - Omitting this keyword has the same assertion behavior as - an empty schema. - - - Implementations MAY choose to implement or optimize this keyword - in another way that produces the same effect, such as by directly - checking the names in "properties" and the patterns in - "patternProperties" against the instance property set. - Implementations that do not support annotation collection MUST do so. - - In defining this option, it seems there is the potential for - ambiguity in the output format. The ambiguity does not affect validation results, - but it does affect the resulting output format. - The ambiguity allows for multiple valid output results depending on whether annotations - are used or a solution that "produces the same effect" as draft-07. It is understood - that annotations from failing schemas are dropped. - See our - [Decision Record](https://github.com/json-schema-org/json-schema-spec/tree/HEAD/adr/2022-04-08-cref-for-ambiguity-and-fix-later-gh-spec-issue-1172.md) - for further details. - - -
- -
- - The value of "propertyNames" MUST be a valid JSON Schema. - - - If the instance is an object, this keyword validates if every property name in - the instance validates against the provided schema. - Note the property name that the schema is testing will always be a string. - - - Omitting this keyword has the same behavior as an empty schema. - -
-
- -
-
- - The value of this keyword MUST be a non-negative integer. - - - This keyword modifies the behavior of "contains" within the same schema object, - as described below in the section for that keyword. - - - Validation MUST always succeed against this keyword. - The value of this keyword is used as its annotation result. - -
- -
- - The value of this keyword MUST be a non-negative integer. - - - This keyword modifies the behavior of "contains" within the same schema object, - as described below in the section for that keyword. - - - Validation MUST always succeed against this keyword. - The value of this keyword is used as its annotation result. - - Per , - omitted keywords MUST NOT produce annotation results. However, as described - in the section for "contains", the absence of this keyword's annotation - causes "contains" to assume a minimum value of 1. - -
- -
- - The value of this keyword MUST be a valid JSON Schema. - - - This keyword applies its subschema to array elements or object property values. - - - An instance is valid against "contains" if the number of elements or property - values that are valid against its subschema is with the inclusive range of - the minimum and (if any) maximum number of occurrences. - - - The maximum number of occurrences is provided by the "maxContains" keyword - within the same schema object as "contains". If "maxContains" is absent, - the maximum number of occurrences MUST be unbounded. - - - The minimum number of occurrences is provided by the "minContains" keyword - within the same schema object as "contains". If "minContains" is absent, - the minimum number of occurrences MUST be 1. - - - Implementations MAY implement the dependency on "minContians" and - "maxContains" by inspecting their values rather than reading annotations - produced by those keywords. - - - This keyword produces an annotation value which is an array of the - indexes or property names to which this keyword validates successfully - when applying its subschema, in ascending order. The value MAY be a - boolean "true" if the subschema validates successfully when applied to - every index or property value of the instance. The annotation MUST be - present if the instance array or object to which this keyword's schema - applies is empty. - - - This annotation affects the behavior of "unevaluatedItems" in the - Unevaluated vocabulary. - - - The subschema MUST be applied to every array element or object property - value even after the first match has been found, in order to collect - annotations for use by other keywords. This is to ensure that all possible - annotations are collected. - -
-
-
-
- -
- - The purpose of these keywords is to enable schema authors to apply - subschemas to array items or object properties that have not been - successfully evaluated against any dynamic-scope subschema of any - adjacent keywords. - - - These instance items or properties may have been unsuccessfully evaluated - against one or more adjacent keyword subschemas, such as when an assertion - in a branch of an "anyOf" fails. Such failed evaluations are not considered - to contribute to whether or not the item or property has been evaluated. - Only successful evaluations are considered. - - - If an item in an array or an object property is "successfully evaluated", it - is logically considered to be valid in terms of the representation of the - object or array that's expected. For example if a subschema represents a car, - which requires between 2-4 wheels, and the value of "wheels" is 6, the instance - object is not "evaluated" to be a car, and the "wheels" property is considered - "unevaluated (successfully as a known thing)", and does not retain any annotations. - - - Recall that adjacent keywords are keywords within the same schema object, - and that the dynamic-scope subschemas include reference targets as well as - lexical subschemas. - - - The behavior of these keywords depend on the annotation results of - adjacent keywords that apply to the instance location being validated. - - - Meta-schemas that do not use "$vocabulary" SHOULD be considered to - require this vocabulary as if its IRI were present with a value of true. - - - The current IRI for this vocabulary, known as the Unevaluated Applicator - vocabulary, is: - <https://json-schema.org/draft/next/vocab/unevaluated>. - - - The current IRI for the corresponding meta-schema is: - . - - -
- - Schema keywords typically operate independently, without - affecting each other's outcomes. However, the keywords in this - vocabulary are notable exceptions: - -
    -
  • - "unevaluatedItems", whose behavior is defined in terms of annotations - from "prefixItems", "items", "contains", and itself -
    • -
  • - "unevaluatedProperties", whose behavior is defined in terms of - annotations from "properties", "patternProperties", - "additionalProperties", "contains", and itself -
    • -
-
- -
- - The value of "unevaluatedItems" MUST be a valid JSON Schema. - - - The behavior of this keyword depends on the annotation results of - adjacent keywords that apply to the instance location being validated. - Specifically, the annotations from "prefixItems", "items", and "contains", - which can come from those keywords when they are adjacent to the - "unevaluatedItems" keyword. Those three annotations, as well as - "unevaluatedItems", can also result from any and all adjacent - in-place applicator keywords. - This includes but is not limited to the in-place applicators - defined in this document. - - - If no relevant annotations are present, the "unevaluatedItems" - subschema MUST be applied to all locations in the array. - If a boolean true value is present from any of the relevant annotations, - "unevaluatedItems" MUST be ignored. Otherwise, the subschema - MUST be applied to any index greater than the largest annotation - value for "prefixItems", which does not appear in any annotation - value for "contains". - - - This means that "prefixItems", "items", "contains", and all in-place - applicators MUST be evaluated before this keyword can be evaluated. - Authors of extension keywords MUST NOT define an in-place applicator - that would need to be evaluated after this keyword. - - - If the "unevaluatedItems" subschema is applied to any - positions within the instance array, it produces an - annotation result of boolean true, analogous to the - behavior of "items". - This annotation affects the behavior of "unevaluatedItems" in parent schemas. - - - Omitting this keyword has the same assertion behavior as - an empty schema. - -
- -
- - The value of "unevaluatedProperties" MUST be a valid JSON Schema. - - - The behavior of this keyword depends on the annotation results of - adjacent keywords that apply to the instance location being validated. - Specifically, the annotations from "properties", "patternProperties", - "contains", and "additionalProperties", which can come from those keywords when - they are adjacent to the "unevaluatedProperties" keyword. Those - four annotations, as well as "unevaluatedProperties", can also - result from any and all adjacent - in-place applicator keywords. - This includes but is not limited to the in-place applicators - defined in this document. - - - Validation with "unevaluatedProperties" applies only to the child - values of instance names that do not appear in the "properties", - "patternProperties", "additionalProperties", "contains", or - "unevaluatedProperties" annotation results that apply to the - instance location being validated. - - - For all such properties, validation succeeds if the child instance - validates against the "unevaluatedProperties" schema. - - - This means that "properties", "patternProperties", "additionalProperties", - "contains" and all in-place applicators MUST be evaluated before this keyword can - be evaluated. Authors of extension keywords MUST NOT define an in-place - applicator that would need to be evaluated after this keyword. - - - The annotation result of this keyword is the set of instance - property names validated by this keyword's subschema. - This annotation affects the behavior of "unevaluatedProperties" in parent schemas. - - - Omitting this keyword has the same assertion behavior as - an empty schema. - -
-
- -
- - JSON Schema is defined to be platform-independent. As such, to increase compatibility - across platforms, implementations SHOULD conform to a standard validation output - format. This section describes the minimum requirements that consumers will need to - properly interpret validation results. - - -
- - JSON Schema output is defined using the JSON Schema data instance model as described - in section 4.2.1. Implementations MAY deviate from this as supported by their - specific languages and platforms, however it is RECOMMENDED that the output be - convertible to the JSON format defined herein via serialization or other means. - -
- -
- - This specification defines three output formats. See the "Output Structure" - section for the requirements of each format. - -
-
Flag
-
- A boolean which simply indicates the overall validation result - with no further details. -
-
List
-
- Provides validation information in a flat list structure. -
-
Hierarchical
-
- Provides validation information in a hierarchical - structure that follows the evaluation paths generated while processing - the schema. -
-
- - An implementation MUST provide the "flag" format and SHOULD provide at least one - of the "list" or "hierarchical" formats. Implementations SHOULD specify in - their documentation which formats they support. - - -
- -
- - Beyond the simplistic "flag" output, additional information is useful to aid in - debugging a schema or instance. Each sub-result SHOULD contain the information - contained within this section at a minimum. - - - A single object that contains all of these components is considered an - output unit. - - - Implementations MAY elect to provide additional information. - - -
- - The evaluation path to the schema object that produced the output unit. - The value MUST be expressed as a JSON Pointer, and it MUST include any - by-reference applicators such as "$ref" or "$dynamicRef". - - The schema may not actually have a value at the location indicated - by this pointer. It is provided as an indication of the traversal - path only. - - - - - Note that this pointer may not be resolvable by the normal JSON Pointer process - due to the inclusion of these by-reference applicator keywords. - - - The JSON key for this information is "evaluationPath". - -
- -
- - The absolute, dereferenced location of the schema object that produced - the output unit. The value MUST be expressed using the canonical IRI of the - relevant schema resource plus a JSON Pointer fragment that indicates the schema - object that produced the output. It MUST NOT include by-reference applicators - such as "$ref" or "$dynamicRef". - - Note that "absolute" here is in the sense of "absolute filesystem path" - (meaning the complete location) rather than the "absolute-IRI" - terminology from RFC 3987 (meaning with scheme and without fragment). - Schema locations will have a fragment in order to identify the specific - schema object. - - - - - - The JSON key for this information is "schemaLocation". - -
- -
- - The location of the JSON value within the instance being validated. The - value MUST be expressed as a JSON Pointer. - - - The JSON key for this information is "instanceLocation". - -
- -
- - Any errors produced by the validation. This property MUST NOT - be included if the validation was successful. The value - for this property MUST be an object where the keys are the names of - keywords and the values are the error message produced by the - associated keyword. - - - If the subschema itself is producing the error, that error MUST be - listed with an empty string key. - - Although there may be other cases where a subschema can produce - an error, the most common case is the "false" schema. In - cases like these, there is no keyword that produces the error, - so there is nothing to use as a key. Thus the empty string - is used instead. - - - - The specific wording for the message is not defined by this - specification. Implementations will need to provide this. - - - The JSON key for this information is "errors". - -
- -
- - Any annotations produced by the evaluation. This property MUST NOT - be included if the validation result of the containing subschema was - unsuccessful. - - - The value for this property MUST be an object where the - keys are the names of keywords and the values are the annotations - produced by the associated keyword. - - - Each keyword defines its own annotation data type (e.g. "properties" - produces a list of keywords, whereas "title" produces a string). - - - The JSON key for this information is "annotations". - -
- -
- - Any annotations produced and subsequently dropped by the evaluation - due to an unsuccessful validation result of the containing subschema. - This property MAY be included if the validation result of the containing - subschema was unsuccessful. It MUST NOT be included if the local - validation result of the containing subschema was successful. - - - Implementations that wish to provide these annotations MUST NOT provide - them as their default behavior. These annotations MUST only be included - by explicitly configuring the implementation to do so. - - - The value for this property MUST be an object where the - keys are the names of keywords and the values are the annotations - produced by the associated keyword. - - - Each keyword defines its own annotation data type (e.g. "properties" - produces a list of keywords, whereas "title" produces a string). - - - The JSON key for this information is "droppedAnnotations". - -
- -
- - Evaluation results generated by applying a subschema to the instance - or a child of the instance. - Keywords which have multiple subschemas (e.g. "anyOf") will generally - generate an output unit for each subschema. In order to accommodate - potentially multiple results, the value of this property MUST be an - array of output units, even if only a single output unit is produced. - - - For "list", this property will appear only at the root output unit - and will hold all output units in a flat list. - - - For "hierarchical", this property will contain results in a tree - structure where each output unit may itself have further nested results. - - - The sequence of output units within this list is not specified and - MAY be determined by the implementation. Sets of output units are - considered equivalent if they contain the same units, in any order. - - - The JSON key for these additional results is "details". - -
- -
- -
- - The output MUST be an object containing a boolean property named "valid". When - additional information about the result is required, the output MUST also contain - "details" as described below. - -
-
valid
-
a boolean value indicating the overall validation success or failure
- -
details
-
the collection of results produced by subschemas
-
- - For these examples, the following schema and instances will be used. - - - - The failing instance will produce the following errors: - -
    -
  • - The value at "/foo" - evaluated at "/properties/foo/allOf/0" - by following the path "/properties/foo/allOf/0" - by the "required" keyword - is missing the property "unspecified-prop". -
    • -
  • - The value at "/foo/foo-prop" - evaluated at "/properties/foo/allOf/1/properties/foo-prop" - by following the path "/properties/foo/allOf/1/properties/foo-prop" - by the "const" keyword - is not the constant value 1. -
    • -
  • - The value at "/bar/bar-prop" - evaluated at "/$defs/bar/properties/bar-prop" - by following the path "/properties/bar/$ref/properties/bar-prop" - by the "type" keyword - is not a number. -
    • -
- - - "minimum" doesn't produce an error because it only operates on - instances that are numbers. - - - Note that the error message wording as depicted in the examples below is not a - requirement of this specification. Implementations SHOULD craft error messages - tailored for their audience or provide a templating mechanism that allows their - users to craft their own messages. - - - - The passing instance will produce the following annotations: - -
    -
  • - The keyword "title" - evaluated at "" - by following the path "" - will produce "root". -
    • -
  • - The keyword "properties" - evaluated at "" - by following the path "" - will produce ["foo", "bar"]. -
    • -
  • - The keyword "title" - evaluated at "/properties/foo" - by following the path "/properties/foo" - will produce "foo-title". -
    • -
  • - The keyword "properties" - evaluated at "/properties/foo/allOf/1" - by following the path "/properties/foo/allOf/1" - will produce ["foo-prop"]. -
    • -
  • - The keyword "additionalProperties" - evaluated at "/properties/foo/allOf/1" - by following the path "/properties/foo/allOf/1" - will produce ["unspecified-prop"]. -
    • -
  • - The keyword "title" - evaluated at "/properties/foo/allOf/1/properties/foo-prop" - by following the path "/properties/foo/allOf/1/properties/foo-prop" - will produce "foo-prop-title". -
    • -
  • - The keyword "title" - evaluated at "/$defs/bar" - by following the path "/properties/bar/$ref" - will produce "bar-title". -
    • -
  • - The keyword "properties" - evaluated at "/$defs/bar" - by following the path "/properties/var/$ref" - will produce ["bar-prop"]. -
    • -
  • - The keyword "title" - evaluated at "/$defs/bar/properties/bar-prop" - by following the path "/properties/bar/$ref/properties/bar-prop" - will produce "bar-prop-title". -
    • -
- -
- - In the simplest case, merely the boolean result for the "valid" valid property - needs to be fulfilled. For this format, all other information is explicitly - omitted. - - - - Because no errors or annotations are returned with this format, it is - RECOMMENDED that implementations use short-circuiting logic to return - failure or success as soon as the outcome can be determined. For example, - if an "anyOf" keyword contains five subschemas, and the second one - passes, there is no need to check the other three. The logic can simply - return with success. - -
- -
- - The "List" structure is a flat list of output units contained within a - root output unit. - - - The root output unit contains "valid" for the overall result and "details" - for the list of specific results. All other information is explicitly - omitted from the root output unit. If the root schema produces errors or - annotations, then the output node for the root MUST be present within the - root output unit's "details" list with those errors or annotations. - - - Output units which do not contain errors or annotations SHOULD be excluded - from this format, however implementations MAY choose to include them for - completeness. - - -
- -
- - The "Hierarchical" structure is a tree structure that follows the - evaluation path during the validation process. Typically, it will - resemble the schema as if all referenced schemas were inlined in place - of their associated by-reference keywords. - - - All output units are included in this format. - - - The location properties of the root output unit MAY be omitted. - - - -
- -
- - For convenience, JSON Schema has been provided to validate output generated - by implementations. Its IRI is: - . - -
- -
- -
- -
- - Both schemas and instances are JSON values. As such, all security considerations - defined in RFC 8259 apply. - - - Instances and schemas are both frequently written by untrusted third parties, to be - deployed on public Internet servers. - Implementations should take care that the parsing and evaluating against schemas - does not consume excessive system resources. - Implementations MUST NOT fall into an infinite loop. - - - A malicious party could cause an implementation to repeatedly collect a copy - of a very large value as an annotation. Implementations SHOULD guard against - excessive consumption of system resources in such a scenario. - - - Servers MUST ensure that malicious parties cannot change the functionality of - existing schemas by uploading a schema with a pre-existing or very similar "$id". - - - Individual JSON Schema vocabularies are liable to also have their own security - considerations. Consult the respective specifications for more information. - - - Schema authors should take care with "$comment" contents, as a malicious - implementation can display them to end-users in violation of a spec, or - fail to strip them if such behavior is expected. - - - A malicious schema author could place executable code or other dangerous - material within a "$comment". Implementations MUST NOT parse or otherwise - take action based on "$comment" contents. - -
- -
-
- - The proposed MIME media type for JSON Schema is defined as follows: - -
-
Type name:
-
application
- -
Subtype name:
-
schema+json
- -
Required parameters:
-
N/A
- -
Encoding considerations:
-
- Encoding considerations are - identical to those specified for the "application/json" - media type. See JSON. -
- -
Security considerations:
-
See above.
- -
Interoperability considerations:
-
- See Sections - , - , and - above. -
- -
Fragment identifier considerations:
-
- See -
-
-
-
- - The proposed MIME media type for JSON Schema Instances that require - a JSON Schema-specific media type is defined as follows: - -
-
Type name:
-
application
- -
Subtype name:
-
schema-instance+json
- -
Required parameters:
-
N/A
- -
Encoding considerations:
-
- Encoding considerations are - identical to those specified for the "application/json" - media type. See JSON. -
- -
Security considerations:
-
See above.
- -
Interoperability considerations:
-
- See Sections - , - , and - above. -
- -
Fragment identifier considerations:
-
See
-
-
-
- - - - - - &RFC2119; - &RFC3986; - &RFC3987; - &RFC6839; - &RFC6901; - &RFC8259; - &ldp; - - - ECMA-262, 11th edition specification - - - - - - - - &RFC6596; - &RFC7049; - &RFC7231; - &RFC8288; - &fragid-best-practices; - &xptr-framework; - - - JSON Schema Validation: A Vocabulary for Structural Validation of JSON - - - - - - - - - - - - - - - - JSON Hyper-Schema: A Vocabulary for Hypermedia Annotation of JSON - - - - - - - - - - - - - Namespaces in XML 1.1 (Second Edition) - - Textuality -
- tbray@textuality.com -
- - - Contivo, Inc. -
- dmh@contivo.com -
- - - Microsoft -
- andrewl@microsoft.com -
- - - University of Edinburgh and Markup Technology Ltd -
- richard@cogsci.ed.ac.uk -
- - - - - - -
- - Consider the following schema, which shows "$id" being used to identify - both the root schema and various subschemas, and "$anchor" being used - to define plain name fragment identifiers. - - - - The schemas at the following IRI-encoded JSON - Pointers (relative to the root schema) have the following - base IRIs, and are identifiable by any listed IRI in accordance with - and above. - -
-
# (document root)
-
-
-
canonical (and base) IRI"
-
https://example.com/root.json
- -
canonical resource IRI plus pointer fragment"
-
https://example.com/root.json#
-
-
- -
#/$defs/A
-
-
-
base IRI
-
https://example.com/root.json
- -
canonical resource IRI plus plain fragment
-
https://example.com/root.json#foo
- -
canonical resource IRI plus pointer fragment
-
https://example.com/root.json#/$defs/A
-
-
- -
#/$defs/B
-
-
-
canonical (and base) IRI
-
https://example.com/other.json
- -
canonical resource IRI plus pointer fragment
-
https://example.com/other.json#
- -
base IRI of enclosing (root.json) resource plus fragment
-
https://example.com/root.json#/$defs/B
-
-
- -
#/$defs/B/$defs/X
-
-
-
base IRI
-
https://example.com/other.json
- -
canonical resource IRI plus plain fragment
-
https://example.com/other.json#bar
- -
canonical resource IRI plus pointer fragment
-
https://example.com/other.json#/$defs/X
- -
base IRI of enclosing (root.json) resource plus fragment
-
https://example.com/root.json#/$defs/B/$defs/X
-
-
- -
#/$defs/B/$defs/Y
-
-
-
canonical (and base) IRI
-
https://example.com/t/inner.json
- -
canonical IRI plus plain fragment
-
https://example.com/t/inner.json#bar
- -
canonical IRI plus pointer fragment
-
https://example.com/t/inner.json#
- -
base IRI of enclosing (other.json) resource plus fragment
-
https://example.com/other.json#/$defs/Y
- -
base IRI of enclosing (root.json) resource plus fragment
-
https://example.com/root.json#/$defs/B/$defs/Y
-
-
- -
#/$defs/C
-
-
-
canonical (and base) IRI
-
urn:uuid:ee564b8a-7a87-4125-8c96-e9f123d6766f
- -
canonical IRI plus pointer fragment
-
urn:uuid:ee564b8a-7a87-4125-8c96-e9f123d6766f#
- -
base IRI of enclosing (root.json) resource plus fragment
-
https://example.com/root.json#/$defs/C
-
-
-
- - Note: The fragment part of the IRI does not make it canonical or non-canonical, - rather, the base IRI used (as part of the full IRI with any fragment) is what - determines the canonical nature of the resulting full IRI. - - Multiple "canonical" IRIs? We Acknowledge this is potentially confusing, and - direct you to read the CREF located in the - JSON Pointer fragments and embedded schema resources - section for futher comments. - - - -
- -
- - Various tools have been created to rearrange schema documents - based on how and where references ("$ref") appear. This appendix discusses - which use cases and actions are compliant with this specification. - -
- - A set of schema resources intended for use together can be organized - with each in its own schema document, all in the same schema document, - or any granularity of document grouping in between. - - - Numerous tools exist to perform various sorts of reference removal. - A common case of this is producing a single file where all references - can be resolved within that file. This is typically done to simplify - distribution, or to simplify coding so that various invocations - of JSON Schema libraries do not have to keep track of and load - a large number of resources. - - - This transformation can be safely and reversibly done as long as - all static references (e.g. "$ref") use IRI-references that resolve - to IRIs using the canonical resource IRI as the base, and all schema - resources have an absolute-IRI as the "$id" in their root schema. - - - With these conditions met, each external resource can be copied - under "$defs", without breaking any references among the resources' - schema objects, and without changing any aspect of validation or - annotation results. The names of the schemas under "$defs" do - not affect behavior, assuming they are each unique, as they - do not appear in the canonical IRIs for the embedded resources. - -
-
- - Attempting to remove all references and produce a single schema document does not, - in all cases, produce a schema with identical behavior to the original form. - - - Since "$ref" is now treated like any other keyword, with other keywords allowed - in the same schema objects, fully supporting non-recursive "$ref" removal in - all cases can require relatively complex schema manipulations. It is beyond - the scope of this specification to determine or provide a set of safe "$ref" - removal transformations, as they depend not only on the schema structure - but also on the intended usage. - -
-
- -
- - Consider the following two schemas describing a simple - recursive tree structure, where each node in the tree - can have a "data" field of any type. The first schema - allows and ignores other instance properties. The second is - more strict and only allows the "data" and "children" properties. - An example instance with "data" misspelled as "daat" is also shown. - - - - When we load these two schemas, we will notice the "$dynamicAnchor" - named "node" (note the lack of "#" as this is just the name) - present in each, resulting in the following full schema IRIs: -
    -
  • "https://example.com/tree#node"
    • -
  • "https://example.com/strict-tree#node"
    • -
- In addition, JSON Schema implementations keep track of the fact - that these fragments were created with "$dynamicAnchor". - - - If we apply the "strict-tree" schema to the instance, we will follow - the "$ref" to the "tree" schema, examine its "children" subschema, - and find the "$dynamicRef": to "#node" (note the "#" for IRI fragment syntax) - in its "items" subschema. That reference resolves to - "https://example.com/tree#node", which is a IRI with a fragment - created by "$dynamicAnchor". Therefore we must examine the dynamic - scope before following the reference. - - - At this point, the evaluation path is - "#/$ref/properties/children/items/$dynamicRef", with a dynamic scope - containing (from the outermost scope to the innermost): -
    -
  1. "https://example.com/strict-tree#"
    2. -
  2. "https://example.com/tree#"
    3. -
  3. "https://example.com/tree#/properties/children"
    4. -
  4. "https://example.com/tree#/properties/children/items"
    5. -
- - - Since we are looking for a plain name fragment, which can be - defined anywhere within a schema resource, the JSON Pointer fragments - are irrelevant to this check. That means that we can remove those - fragments and eliminate consecutive duplicates, producing: -
    -
  1. "https://example.com/strict-tree"
    2. -
  2. "https://example.com/tree"
    3. -
- - - In this case, the outermost resource also has a "node" fragment - defined by "$dynamicAnchor". Therefore instead of resolving the - "$dynamicRef" to "https://example.com/tree#node", we resolve it to - "https://example.com/strict-tree#node". - - - This way, the recursion in the "tree" schema recurses to the root - of "strict-tree", instead of only applying "strict-tree" to the - instance root, but applying "tree" to instance children. - - - This example shows both "$dynamicAnchor"s in the same place - in each schema, specifically the resource root schema. - Since plain-name fragments are independent of the JSON structure, - this would work just as well if one or both of the node schema objects - were moved under "$defs". It is the matching "$dynamicAnchor" values - which tell us how to resolve the dynamic reference, not any sort of - correlation in JSON structure. - -
- -
-
- - Vocabulary authors should - take care to avoid keyword name collisions if the vocabulary is intended - for broad use, and potentially combined with other vocabularies. JSON - Schema does not provide any formal namespacing system, but also does - not constrain keyword names, allowing for any number of namespacing - approaches. - - - Vocabularies may build on each other, such as by defining the behavior - of their keywords with respect to the behavior of keywords from another - vocabulary, or by using a keyword from another vocabulary with - a restricted or expanded set of acceptable values. Not all such - vocabulary re-use will result in a new vocabulary that is compatible - with the vocabulary on which it is built. Vocabulary authors should - clearly document what level of compatibility, if any, is expected. - - - Meta-schema authors should not use "$vocabulary" to combine multiple - vocabularies that define conflicting syntax or semantics for the same - keyword. As semantic conflicts are not generally detectable through - schema validation, implementations are not expected to detect such - conflicts. If conflicting vocabularies are declared, the resulting - behavior is undefined. - - - Vocabulary authors SHOULD provide a meta-schema that validates the - expected usage of the vocabulary's keywords on their own. Such meta-schemas - SHOULD not forbid additional keywords, and MUST not forbid any - keywords from the Core vocabulary. - - - It is recommended that meta-schema authors reference each vocabulary's - meta-schema using the "allOf" keyword, - although other mechanisms for constructing the meta-schema may be - appropriate for certain use cases. - - - The recursive nature of meta-schemas makes the "$dynamicAnchor" - and "$dynamicRef" keywords particularly useful for extending - existing meta-schemas, as can be seen in the JSON Hyper-Schema meta-schema - which extends the Validation meta-schema. - - - Meta-schemas may impose additional constraints, including describing - keywords not present in any vocabulary, beyond what the meta-schemas - associated with the declared vocabularies describe. This allows for - restricting usage to a subset of a vocabulary, and for validating - locally defined keywords not intended for re-use. - - - However, meta-schemas should not contradict any vocabularies that - they declare, such as by requiring a different JSON type than - the vocabulary expects. The resulting behavior is undefined. - - - Meta-schemas intended for local use, with no need to test for - vocabulary support in arbitrary implementations, can safely omit - "$vocabulary" entirely. - -
- -
- - This meta-schema explicitly declares both the Core and Applicator vocabularies, - together with an extension vocabulary, and combines their meta-schemas with - an "allOf". The extension vocabulary's meta-schema, which describes only the - keywords in that vocabulary, is shown after the main example meta-schema. - - - The main example meta-schema also restricts the usage of the Unevaluated - vocabulary by forbidding the keywords prefixed with "unevaluated", which - are particularly complex to implement. This does not change the semantics - or set of keywords defined by the other vocabularies. It just ensures - that schemas using this meta-schema that attempt to use the keywords - prefixed with "unevaluated" will fail validation against this meta-schema. - - - Finally, this meta-schema describes the syntax of a keyword, "localKeyword", - that is not part of any vocabulary. Presumably, the implementors and users - of this meta-schema will understand the semantics of "localKeyword". - JSON Schema does not define any mechanism for expressing keyword semantics - outside of vocabularies, making them unsuitable for use except in a - specific environment in which they are understood. - - - This meta-schema combines several vocabularies for general use. - - - - This meta-schema describes only a single extension vocabulary. - - - - As shown above, even though each of the single-vocabulary meta-schemas - referenced in the general-use meta-schema's "allOf" declares its - corresponding vocabulary, this new meta-schema must re-declare them. - - - The standard meta-schemas that combine all vocabularies defined by - the Core and Validation specification, and that combine all vocabularies - defined by those specifications as well as the Hyper-Schema specification, - demonstrate additional complex combinations. These IRIs for these - meta-schemas may be found in the Validation and Hyper-Schema specifications, - respectively. - - - While the general-use meta-schema can validate the syntax of "minDate", - it is the vocabulary that defines the logic behind the semantic meaning - of "minDate". Without an understanding of the semantics (in this example, - that the instance value must be a date equal to or after the date - provided as the keyword's value in the schema), an implementation can - only validate the syntactic usage. In this case, that means validating - that it is a date-formatted string (using "pattern" to ensure that it is - validated even when "format" functions purely as an annotation, as explained - in the Validation specification. - -
-
- -
- - While the presence of references is expected to be transparent - to validation results, generative use cases such as code generators - and UI renderers often consider references to be semantically significant. - - - To make such use case-specific semantics explicit, the best practice - is to create an annotation keyword for use in the same - schema object alongside of a reference keyword such as "$ref". - - - For example, here is a hypothetical keyword for determining - whether a code generator should consider the reference - target to be a distinct class, and how those classes are related. - Note that this example is solely for illustrative purposes, and is - not intended to propose a functional code generation keyword. - - - - Here, this schema represents some sort of object-oriented class. - The first reference in the "allOf" is noted as the base class. - The second is not assigned a class relationship, meaning that the - code generator should combine the target's definition with this - one as if no reference were involved. - - - Looking at the properties, "foo" is flagged as object composition, - while the "date" property is not. It is simply a field with - sub-fields, rather than an instance of a distinct class. - - - This style of usage requires the annotation to be in the same object - as the reference, which must be recognizable as a reference. - -
- -
- - Thanks to - Gary Court, - Francis Galiegue, - Kris Zyp, - and Geraint Luff - for their work on the initial drafts of JSON Schema. - - - Thanks to - Jason Desrosiers, - Daniel Perrett, - Erik Wilde, - Evgeny Poberezkin, - Brad Bowman, - Gowry Sankar, - Donald Pipowitch, - Dave Finlay, - Denis Laxalde, - Phil Sturgeon, - Shawn Silverman, - and Karen Etheridge - for their submissions and patches to the document. - -
- -
- - This section to be removed before leaving Internet-Draft status. - - -
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  • Improve and clarify the "type", "contains", "unevaluatedProperties", and "unevaluatedItems" keyword explanations
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  • Clarify Vocabularies need not be formally defined
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  • Removed reference to draft-pbryan-zyp-json-ref-03
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- - diff --git a/jsonschema-use-cases.md b/jsonschema-use-cases.md new file mode 100644 index 00000000..7c180636 --- /dev/null +++ b/jsonschema-use-cases.md @@ -0,0 +1,370 @@ +--- +v: 3 +ipr: none +docname: draft-wright-jsonschema-use-cases-00 +cat: info +submissiontype: independent +title: 'JSON Schema: Use Cases and Requirements' +abbrev: JSON Schema +wg: JSON Schema +kw: JSON +date: 2023 +author: +- role: editor + ins: A. Wright + name: Austin Wright + org: '' + email: aaa@bzfx.net +informative: + RFC5234: + RFC6906: + +--- abstract + + +To foster development of JSON Schema, this document contains a list of use +cases and requirements that may be used to inform its development and evolution. + +--- note_Note_to_Readers + +The issues list for this document can be found at +[](https://github.com/json-schema-org/json-schema-spec/issues). + +For additional information, see [](https://json-schema.org/). + +To provide feedback, use this issue tracker, the communication methods +listed on the homepage, or email the document editors. + +--- middle + +# Scope and Motivation + +JSON Schema is a JSON media type for defining the structure of JSON data. +JSON Schema +is intended to define validation, documentation, hyperlink navigation, and +interaction +control of JSON data. + +This document elaborates in detail what this means, and the specific use +cases that shall be supported. + + +# Conventions and Terminology + +Objectives specify the class of problems that are in the scope of the specification. + +Use Cases catalog a variety of personal objectives that users may have, due +to various motivations and constraints, that the specification shall accommodate, +but without prescribing a specific design or implementation. + +Requirements list functional, non-functional, and quality requirements, the +use cases they may be derived from/related to, and reference how each use +case is implemented. Requirements are not detailed at this time but may be +specified in the future. + + +# Objectives + +JSON Schema shall be built to support the following objectives, supporting +expansion into uses not currently described by any use case, but which fall +within the objectives. + +## Validation + +The first objective of JSON Schema is to describe sets of JSON documents; +specifically, to notate a language of JSON documents using a machine-readable, +set-builder notation. +This covers the key use case of validating input using a validator, as well +as numerous other tools that depend on describing to each other which kinds +of JSON documents are and are not acceptable. + + +## Annotation + +The second objective of JSON Schema is to map an input JSON document to an +arbitrary output described by the user. +Annotations may be combined with validation (in the same schema) to specify +the domain of inputs for which an output is defined. +This covers the key use case of documenting the meaning of properties and +values in JSON documents, and other uses where the input document is being +interpreted in some fashion. + + +## Internet + +JSON is a technology standardized as a part of a larger ecosystem of Internet +technology, and likewise, JSON Schema may also specify its role in this ecosystem; +for example, use in HTTP, or the meaning of media type parameters. + + +## Out of scope + +Use cases or requirements that do not advance these objectives are likely +out of scope, and better suited in separate work that references JSON Schema. + +For example, a method of describing an API interface would exceed the scope +of JSON Schema, although JSON Schema may be used as a part of such a description, +such as when the API is using JSON and needs a way to describe these JSON +documents. + + + +# Use Cases + +JSON Schema shall be written to standardize these use cases, or shall accommodate +implementations targeted at these uses. + +## Structural validation {#uc-structural} + +Structural validation refers to the "structure" that a JSON document is supposed +to follow, such as which properties must exist, what types of values are +expected where, and what they must look like. Constraints cannot read values +elsewhere in the document (e.g. to compare two values for equality), though +constraints may depend on "where" the value is found (e.g. specific properties +or array items must be a number). + +More specifically, structural validation is any validation that can be performed +with a context-free grammar that follows JSON semantics, such that any forms +that are equal according to JSON will produce the same result. + +Validators that support structural validation can entirely replace generic +grammar languages such as [ABNF](#RFC5234), and will guarantee compliance with +JSON semantics. Likewise, schemas whose +validation rules are limited to structural validation can be executed using +a deterministic pushdown automata, guaranteeing a result in proportional +time without error. + +The following features of JSON are structural validation: + + + +> JSON primitive type (string, object, etc) + +> Minimum or maximum in a linear range of values + +> Minimum or maximum lengths (number of characters, digits, items, or properties) + +> Literal/constant values or alternate/enumerated values + +> Pattern matching strings by a regular expression (including object keys) + +> Logic operators (union, intersection, difference) + +> Descent into object properties and array items (recursively) + + + + +Multiple forms that are value-equal according to JSON are not distinguishable +under this use-case. This includes the ordering of properties in an object, +character escapes in strings, and whitespace. + + +## Semantic annotation {#uc-annotations} + +There is a need to annotate values within a JSON document: for machine readability, +and for documentation purposes. +Given a document and directions for annotating it, you should should be able +to: + + + +> document the meaning of a property, + +> suggest a default value for new documents of a given type, + +> fill in missing values (in objects or arrays) with values of equivalent meaning, + +> generate a list of hyperlinks, + +> or declare relationships between data. + + + + +A schema may be used to describe a machine-readable [profile](#RFC6906) of JSON +document. Even when two schemas identify the same set of JSON documents; +depending on the context, a given JSON document may be a profile of one but +not the other. + + +## Domain-specific language + +Developers may write an application that uses a JSON Schema internally as +a domain-specific language, so that the schema is only used inside a single +application by a single party. By using a declarative language, the application +requirements can be optimized better than a human could do. + +Application authors may use a schema to define custom hooks and processing +for the JSON (without need for standardizing the customization). + +The only interoperability consideration here is that updates to the validator +library must not change the validation result of any JSON documents, unless +the developer specifically opts into such a breaking change (e.g. by upgrading +the library to a new major version number). + + +## A common vocabulary + +A development team maintains two similar applications, but for different +platforms, in different languages. The application downloads and reads from +a common repository of JSON documents. They want to make sure that both applications +accept or reject JSON with identical behavior, so they write a single JSON +Schema and deploy it to both applications. + +The only interoperability consideration here is that the two applications, +given the same schema, must both be reasonably expected to support the same +behavior and operate in the same manner. + + +## Model-Driven UI constraints + +When a server declares constraints that a submission must meet, there is +a need for the user interface to receive these constraints to provide model-driven +validation of permissible values, making the form more accessible to the +user. + +For example, if a value is specified to be a date, the form field where the +value is specified can provide immediate feedback if an invalid date is entered, +and even offer a date picker to help the user input a correct value. + +Weak interoperability requirements can hamper the user experience within +this use case. If the schema is ambiguous in any way, or is up to the discretion +of the customer's user-agent, some customers may have a difficult time submitting +a correct request. + + +## Fuzzing, enumeration, and generation + +Security applications need to generate examples of JSON documents within +the valid set, and outside the valid set. + + +## Embedded database constraints + +A database that uses JSON may need a way to declare, enforce, or guarantee +certain constraints on the JSON document being stored. The database may also +use JSON Schema as a way to annotate certain fields as having a special meaning +for uniqueness or indexing purposes. + + +## Partial validation {#partial-validation} + +Due to technical limitations, some JSON parsers may only be able to understand +a subset of the JSON value space, and it makes sense to validate the value +read by the application, instead of the JSON document provided to the JSON +parser. For example: + + + +* Many JSON parsers cast the arbitrary-precision decimal numbers to an IEEE + floating point, validating the number after it has lost some precision. + +* Some programming languages cannot distinguish between an ordered array of + values and a key-value map; or an empty array is identical to an empty object. + +* Other validators may have a limited amount of memory and cannot support assertions + more complicated than a deterministic context-free grammar. + + +Users of these validators need a way to determine if the missing functionality +is essential to correctly validating input, and if not, get a validation +result that would be correct but-for the unimplemented functionality. + +[^CREF1] + +[^CREF1]: There's two directions this can work: an application should be able to + determine if a third-party schema is making a distinction that it does not + support; and an application may want to publish a schema indicating it works + in a reduced value space. + + + +## Machine-readable profiles of Web resources + +A Web server that offers a JSON document should be able to link to a profile +document that describes the meaning of the data in a machine-readable form. + + +## Hypermedia + +Generic user-agents must be able to make use of the schema as it evolves, +including Web browsers, spiders, and automated tooling. It should support +loose coupling (like an HTML homepage); so a schema should be able to change, +add, and remove features with minimal breakage for compatible clients. + + +## Results and Reporting + +The party that is providing the schema and input may not be the same party +that is performing the validation; in this case, there should be a standard +way to abstract away the validator interface, and report the results of a +validation operation (validation result, annotations, and errors). + + +## Extension points {#extension-points} + +Not every feature needs to be supported by every implementation. +To accommodate a wide variety of niche audiences, it should be possible to +specify features that are optional to implement. +This includes standardized features that are optional to implement, bespoke +or user-defined features that are not standardized, and new features added +to future publications of the specification. +For forward compatibility, implementations that do not support optional extensions +must degrade in a predictable fashion. + + +## External validation + +Authors may embed resources of other media types, such as text documents, +or base64 or hex-encoded binary documents; and may wish to pass off validation +of these documents to another software tool. + + +## Intra-document data consistency validation + +A JSON document may carry relational data that must be internally consistent. +Example constraints include: + + +* One-to-one calculations, like that children's birthdates come after their + parent's birthdates; + +* One-to-many calculations, like a reference to an anchor points to an anchor + defined somewhere in the same document. + + +## Inter-database consistency validation + +A JSON document may carry relational data that must be verified against outside +data sources. Example constraints include: + + +* References to a user ID points to a user in a central users database. + +* A supplied email address has been verified by the user. + + +## Linting + +Sometimes it's desirable to require formatting that does not impact the application-level +meaning of the document, but instead specifies requirements purely for aesthetic +or compatibility reasons. + +For example, for security reasons, an application may want to verify a JSON +document does not contain the string "`` tag, it could not close the tag and be interpreted as HTML. + +This is not a standard part of JSON Schema because it may violate the semantics +of JSON, by adding an ability to distinguish between encodings which are +supposed to be equivalent to receiving applications. + + + +# Security Considerations {#security} + +This document does not make any normative requirements. + + +--- back diff --git a/jsonschema-use-cases.xml b/jsonschema-use-cases.xml deleted file mode 100644 index 55cb770d..00000000 --- a/jsonschema-use-cases.xml +++ /dev/null @@ -1,310 +0,0 @@ - - - - - -]> - - - - - - - - - - - JSON Schema: Use Cases and Requirements - - -
- aaa@bzfx.net -
- - - - JSON Schema - JSON - Schema - Hyper Schema - Hypermedia - - - - To foster development of JSON Schema, this document contains a list of use cases and requirements that may be used to inform its development and evolution. - - - - - The issues list for this document can be found at - . - - - For additional information, see . - - - To provide feedback, use this issue tracker, the communication methods listed on the - homepage, or email the document editors. - - - - - -
- - JSON Schema is a JSON media type for defining the structure of JSON data. JSON Schema - is intended to define validation, documentation, hyperlink navigation, and interaction - control of JSON data. - - - This document elaborates in detail what this means, and the specific use cases that shall be supported. - -
- -
- - Objectives specify the class of problems that are in the scope of the specification. - - - - Use Cases catalog a variety of personal objectives that users may have, due to various motivations and constraints, that the specification shall accommodate, but without prescribing a specific design or implementation. - - - - Requirements list functional, non-functional, and quality requirements, the use cases they may be derived from/related to, and reference how each use case is implemented. Requirements are not detailed at this time but may be specified in the future. - -
- -
- - JSON Schema shall be built to support the following objectives, supporting expansion into uses not currently described by any use case, but which fall within the objectives. - - -
- - The first objective of JSON Schema is to describe sets of JSON documents; specifically, to notate a language of JSON documents using a machine-readable, set-builder notation. - This covers the key use case of validating input using a validator, as well as numerous other tools that depend on describing to each other which kinds of JSON documents are and are not acceptable. - -
- -
- - The second objective of JSON Schema is to map an input JSON document to an arbitrary output described by the user. - Annotations may be combined with validation (in the same schema) to specify the domain of inputs for which an output is defined. - This covers the key use case of documenting the meaning of properties and values in JSON documents, and other uses where the input document is being interpreted in some fashion. - -
- -
- - JSON is a technology standardized as a part of a larger ecosystem of Internet technology, and likewise, JSON Schema may also specify its role in this ecosystem; for example, use in HTTP, or the meaning of media type parameters. - -
- -
- - Use cases or requirements that do not advance these objectives are likely out of scope, and better suited in separate work that references JSON Schema. - - - For example, a method of describing an API interface would exceed the scope of JSON Schema, although JSON Schema may be used as a part of such a description, such as when the API is using JSON and needs a way to describe these JSON documents. - -
- -
- -
- - JSON Schema shall be written to standardize these use cases, or shall accommodate implementations targeted at these uses. - - -
- - Structural validation refers to the "structure" that a JSON document is supposed to follow, such as which properties must exist, what types of values are expected where, and what they must look like. Constraints cannot read values elsewhere in the document (e.g. to compare two values for equality), though constraints may depend on "where" the value is found (e.g. specific properties or array items must be a number). - - - More specifically, structural validation is any validation that can be performed with a context-free grammar that follows JSON semantics, such that any forms that are equal according to JSON will produce the same result. - - - Validators that support structural validation can entirely replace generic grammar languages such as ABNF, and will guarantee compliance with JSON semantics. Likewise, schemas whose validation rules are limited to structural validation can be executed using a deterministic pushdown automata, guaranteeing a result in proportional time without error. - - - The following features of JSON are structural validation: - - - JSON primitive type (string, object, etc) - Minimum or maximum in a linear range of values - Minimum or maximum lengths (number of characters, digits, items, or properties) - Literal/constant values or alternate/enumerated values - Pattern matching strings by a regular expression (including object keys) - Logic operators (union, intersection, difference) - Descent into object properties and array items (recursively) - - - Multiple forms that are value-equal according to JSON are not distinguishable under this use-case. This includes the ordering of properties in an object, character escapes in strings, and whitespace. - -
- -
- - There is a need to annotate values within a JSON document: for machine readability, and for documentation purposes. - Given a document and directions for annotating it, you should should be able to: - - - document the meaning of a property, - suggest a default value for new documents of a given type, - fill in missing values (in objects or arrays) with values of equivalent meaning, - generate a list of hyperlinks, - or declare relationships between data. - - - A schema may be used to describe a machine-readable profile of JSON document. Even when two schemas identify the same set of JSON documents; depending on the context, a given JSON document may be a profile of one but not the other. - -
- -
- - Developers may write an application that uses a JSON Schema internally as a domain-specific language, so that the schema is only used inside a single application by a single party. By using a declarative language, the application requirements can be optimized better than a human could do. - - - Application authors may use a schema to define custom hooks and processing for the JSON (without need for standardizing the customization). - - - The only interoperability consideration here is that updates to the validator library must not change the validation result of any JSON documents, unless the developer specifically opts into such a breaking change (e.g. by upgrading the library to a new major version number). - -
- -
- - A development team maintains two similar applications, but for different platforms, in different languages. The application downloads and reads from a common repository of JSON documents. They want to make sure that both applications accept or reject JSON with identical behavior, so they write a single JSON Schema and deploy it to both applications. - - - The only interoperability consideration here is that the two applications, given the same schema, must both be reasonably expected to support the same behavior and operate in the same manner. - -
- -
- - When a server declares constraints that a submission must meet, there is a need for the user interface to receive these constraints to provide model-driven validation of permissible values, making the form more accessible to the user. - - - For example, if a value is specified to be a date, the form field where the value is specified can provide immediate feedback if an invalid date is entered, and even offer a date picker to help the user input a correct value. - - - Weak interoperability requirements can hamper the user experience within this use case. If the schema is ambiguous in any way, or is up to the discretion of the customer's user-agent, some customers may have a difficult time submitting a correct request. - -
- -
- - Security applications need to generate examples of JSON documents within the valid set, and outside the valid set. - -
- -
- - A database that uses JSON may need a way to declare, enforce, or guarantee certain constraints on the JSON document being stored. The database may also use JSON Schema as a way to annotate certain fields as having a special meaning for uniqueness or indexing purposes. - -
- -
- - Due to technical limitations, some JSON parsers may only be able to understand a subset of the JSON value space, and it makes sense to validate the value read by the application, instead of the JSON document provided to the JSON parser. For example: - - - Many JSON parsers cast the arbitrary-precision decimal numbers to an IEEE floating point, validating the number after it has lost some precision. - Some programming languages cannot distinguish between an ordered array of values and a key-value map; or an empty array is identical to an empty object. - Other validators may have a limited amount of memory and cannot support assertions more complicated than a deterministic context-free grammar. - - - Users of these validators need a way to determine if the missing functionality is essential to correctly validating input, and if not, get a validation result that would be correct but-for the unimplemented functionality. - - - - There's two directions this can work: an application should be able to determine if a third-party schema is making a distinction that it does not support; and an application may want to publish a schema indicating it works in a reduced value space. - - -
- -
- - A Web server that offers a JSON document should be able to link to a profile document that describes the meaning of the data in a machine-readable form. - -
- -
- - Generic user-agents must be able to make use of the schema as it evolves, including Web browsers, spiders, and automated tooling. It should support loose coupling (like an HTML homepage); so a schema should be able to change, add, and remove features with minimal breakage for compatible clients. - -
- -
- - The party that is providing the schema and input may not be the same party that is performing the validation; in this case, there should be a standard way to abstract away the validator interface, and report the results of a validation operation (validation result, annotations, and errors). - -
- -
- - Not every feature needs to be supported by every implementation. - To accommodate a wide variety of niche audiences, it should be possible to specify features that are optional to implement. - This includes standardized features that are optional to implement, bespoke or user-defined features that are not standardized, and new features added to future publications of the specification. - For forward compatibility, implementations that do not support optional extensions must degrade in a predictable fashion. - -
- -
- - Authors may embed resources of other media types, such as text documents, or base64 or hex-encoded binary documents; and may wish to pass off validation of these documents to another software tool. - -
- -
- - A JSON document may carry relational data that must be internally consistent. Example constraints include: - -
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- - Sometimes it's desirable to require formatting that does not impact the application-level meaning of the document, but instead specifies requirements purely for aesthetic or compatibility reasons. - - - For example, for security reasons, an application may want to verify a JSON document does not contain the string "</script" but is written instead with a character escape such as "<\/script". This would ensure that, if the JSON were to be embedded in a <script> tag, it could not close the tag and be interpreted as HTML. - - - This is not a standard part of JSON Schema because it may violate the semantics of JSON, by adding an ability to distinguish between encodings which are supposed to be equivalent to receiving applications. - -
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- -
- - This document does not make any normative requirements. - -
- - - - - - &RFC5234; - &RFC6906; - - - - diff --git a/jsonschema-validation.md b/jsonschema-validation.md new file mode 100644 index 00000000..600b2ae8 --- /dev/null +++ b/jsonschema-validation.md @@ -0,0 +1,1383 @@ +--- +v: 3 +docname: draft-bhutton-json-schema-validation-01 +cat: info +submissiontype: IETF +title: 'JSON Schema Validation: A Vocabulary for Structural Validation of JSON' +abbrev: JSON Schema Validation +wg: Internet Engineering Task Force +kw: JSON +date: 2023 +author: +- role: editor + ins: A. Wright + name: Austin Wright + org: '' + email: aaa@bzfx.net +- role: editor + ins: H. Andrews + name: Henry Andrews + org: '' + email: andrews_henry@yahoo.com +- role: editor + ins: B. Hutton + name: Ben Hutton + org: Postman + email: ben@jsonschema.dev + uri: https://jsonschema.dev +normative: + RFC1123: + RFC2045: + RFC2046: + RFC2673: + RFC3339: + RFC3986: + RFC3987: + RFC4122: + RFC4291: + RFC4648: + RFC5321: + RFC5890: + RFC5891: + RFC6570: + RFC6531: + RFC6901: + RFC8259: + ecma262: + target: https://www.ecma-international.org/ecma-262/11.0 + title: ECMA-262, 11th edition specification + author: + - org: '' + date: 2020-06 + relative-json-pointer: + title: Relative JSON Pointers + author: + - ins: G. Luff + org: '' + - ins: H. Andrews + org: Cloudflare, Inc. + - role: editor + ins: B. Hutton + name: Ben Hutton + org: '' + date: 2020-12 + seriesinfo: + Internet-Draft: draft-handrews-relative-json-pointer-01 + json-schema: + title: 'JSON Schema: A Media Type for Describing JSON Documents' + author: + - ins: A. Wright + org: '' + - ins: H. Andrews + org: '' + - ins: B. Hutton + org: '' + - ins: G. Dennis + org: '' + date: 2022-06 + seriesinfo: + Internet-Draft: draft-bhutton-json-schema-01 +informative: + RFC4329: + +--- abstract + + +JSON Schema (application/schema+json) has several purposes, one of which +is JSON +instance validation. +This document specifies a vocabulary for JSON Schema to describe the meaning +of JSON +documents, provide hints for user interfaces working with JSON data, and +to make +assertions about what a valid document must look like. + +--- note_Note_to_Readers + +The issues list for this draft can be found at +[](https://github.com/json-schema-org/json-schema-spec/issues). + +For additional information, see [](https://json-schema.org/). + +To provide feedback, use this issue tracker, the communication methods listed +on the +homepage, or email the document editors. + +--- middle + +# Introduction + +JSON Schema can be used to require that a given JSON document (an instance) +satisfies a certain number of criteria. These criteria are asserted by using +keywords described in this specification. In addition, a set of keywords +is also defined to assist in interactive user interface instance generation. + +This specification will use the concepts, syntax, and terminology defined +by the [JSON Schema core](#json-schema) specification. + + +# Conventions and Terminology + +{::boilerplate bcp14-tagged} + +This specification uses the term "container instance" to refer to both array +and +object instances. It uses the term "children instances" to refer to array +elements +or object member values. + +Elements in an array value are said to be unique if no two elements of this +array +are [equal](#json-schema). + + +# Overview + +JSON Schema validation asserts constraints on the structure of instance data. +An instance location that satisfies all asserted constraints is then +annotated with any keywords that contain non-assertion information, +such as descriptive metadata and usage hints. If all locations within +the instance satisfy all asserted constraints, then the instance is +said to be valid against the schema. + +Each schema object is independently evaluated against each instance location +to which it applies. This greatly simplifies the implementation requirements +for validators by ensuring that they do not need to maintain state across +the document-wide validation process. + +This specification defines a set of assertion keywords, as well as a small +vocabulary +of metadata keywords that can be used to annotate the JSON instance with +useful information. The {{format}} keyword is intended primarily +as an annotation, but can optionally be used as an assertion. +The {{content}} keywords are annotations for working with documents +embedded as JSON strings. + + +# Interoperability Considerations + +## Validation of String Instances + +It should be noted that the nul character (\u0000) is valid in a JSON string. +An +instance to validate may contain a string value with this character, regardless +of the ability of the underlying programming language to deal with such data. + + +## Validation of Numeric Instances + +The JSON specification allows numbers with arbitrary precision, and JSON +Schema +does not add any such bounds. +This means that numeric instances processed by JSON Schema can be arbitrarily +large and/or +have an arbitrarily long decimal part, regardless of the ability of the +underlying programming language to deal with such data. + + +## Regular Expressions {#regexInterop} + +Keywords that use regular expressions, or constrain the instance value +to be a regular expression, are subject to the interoperability +considerations for regular expressions in the +[JSON Schema Core](#json-schema) specification. + + + +# Meta-Schema {#meta-schema} + +The current IRI for the default JSON Schema dialect meta-schema is +[](https://json-schema.org/draft/next/schema). +For schema author convenience, this meta-schema describes a dialect +consisting of all vocabularies +defined in this specification and the JSON Schema Core specification, +as well as two former keywords which are reserved for a transitional period. +Individual vocabulary and vocabulary meta-schema IRIs are given for +each section below. Certain vocabularies are optional to support, which +is explained in detail in the relevant sections. + +Updated vocabulary and meta-schema IRIs MAY be published between +specification drafts in order to correct errors. Implementations +SHOULD consider IRIs dated after this specification draft and +before the next to indicate the same syntax and semantics +as those listed here. + + +# A Vocabulary for Structural Validation + +Validation keywords in a schema impose requirements for successful validation +of an +instance. These keywords are all assertions without any annotation behavior. + +Meta-schemas that do not use "$vocabulary" SHOULD be considered to +require this vocabulary as if its IRI were present with a value of true. + +The current IRI for this vocabulary, known as the Validation vocabulary, +is: +\. + +The current IRI for the corresponding meta-schema is: +[](https://json-schema.org/draft/next/meta/validation). + +## Validation Keywords for Any Instance Type {#general} + +### type + +The value of this keyword MUST be either a string or an array. If it is +an array, elements of the array MUST be strings and MUST be unique. + +String values MUST be one of the six primitive types +("null", "boolean", "object", "array", "number", or "string"), +or "integer" which matches any number with a zero fractional part. + +If the value of "type" is a string, then an instance validates successfully +if +its type matches the type represented by the value of the string. +If the value of "type" is an array, then an instance validates successfully +if +its type matches any of the types indicated by the strings in the array. + + +### enum {#enum} + +The value of this keyword MUST be an array. This array SHOULD have at +least one element. Elements in the array SHOULD be unique. + +An instance validates successfully against this keyword if its value is +equal to one of the elements in this keyword's array value. + +Elements in the array might be of any type, including null. + + +### const + +The value of this keyword MAY be of any type, including null. + +Use of this keyword is functionally equivalent to an ["enum"](#enum) +with a single value. + +An instance validates successfully against this keyword if its value is +equal to the value of the keyword. + + + +## Validation Keywords for Numeric Instances (number and integer) {#numeric} + +### multipleOf + +The value of "multipleOf" MUST be a number, strictly greater than 0. + +A numeric instance is valid only if division by this keyword's value results +in +an integer. + + +### maximum + +The value of "maximum" MUST be a number, representing an inclusive upper +limit +for a numeric instance. + +If the instance is a number, then this keyword validates only if the instance +is +less than or exactly equal to "maximum". + + +### exclusiveMaximum + +The value of "exclusiveMaximum" MUST be a number, representing an exclusive +upper +limit for a numeric instance. + +If the instance is a number, then the instance is valid only if it has a +value +strictly less than (not equal to) "exclusiveMaximum". + + +### minimum + +The value of "minimum" MUST be a number, representing an inclusive lower +limit +for a numeric instance. + +If the instance is a number, then this keyword validates only if the instance +is +greater than or exactly equal to "minimum". + + +### exclusiveMinimum + +The value of "exclusiveMinimum" MUST be a number, representing an exclusive +lower +limit for a numeric instance. + +If the instance is a number, then the instance is valid only if it has a +value +strictly greater than (not equal to) "exclusiveMinimum". + + + +## Validation Keywords for Strings {#string} + +### maxLength + +The value of this keyword MUST be a non-negative integer. + +A string instance is valid against this keyword if its +length is less than, or equal to, the value of this keyword. + +The length of a string instance is defined as the number of its +characters as defined by [RFC 8259](#RFC8259). + + +### minLength + +The value of this keyword MUST be a non-negative integer. + +A string instance is valid against this keyword if its +length is greater than, or equal to, the value of this keyword. + +The length of a string instance is defined as the number of its +characters as defined by [RFC 8259](#RFC8259). + +Omitting this keyword has the same behavior as a value of 0. + + +### pattern {#pattern} + +The value of this keyword MUST be a string. This string SHOULD be a +valid regular expression, according to the ECMA-262 regular expression +dialect. + +A string instance is considered valid if the regular +expression matches the instance successfully. Recall: regular +expressions are not implicitly anchored. + + + +## Validation Keywords for Arrays + +### maxItems + +The value of this keyword MUST be a non-negative integer. + +An array instance is valid against "maxItems" if its size is +less than, or equal to, the value of this keyword. + + +### minItems + +The value of this keyword MUST be a non-negative integer. + +An array instance is valid against "minItems" if its size is +greater than, or equal to, the value of this keyword. + +Omitting this keyword has the same behavior as a value of 0. + + +### uniqueItems + +The value of this keyword MUST be a boolean. + +If this keyword has boolean value false, the instance validates +successfully. If it has boolean value true, the instance validates +successfully if all of its elements are unique. + +Omitting this keyword has the same behavior as a value of false. + + + +## Validation Keywords for Objects + +### maxProperties + +The value of this keyword MUST be a non-negative integer. + +An object instance is valid against "maxProperties" if its +number of properties is less than, or equal to, the value of this +keyword. + + +### minProperties + +The value of this keyword MUST be a non-negative integer. + +An object instance is valid against "minProperties" if its +number of properties is greater than, or equal to, the value of this +keyword. + +Omitting this keyword has the same behavior as a value of 0. + + +### required + +The value of this keyword MUST be an array. +Elements of this array, if any, MUST be strings, and MUST be unique. + +An object instance is valid against this keyword if every item in the array +is +the name of a property in the instance. + +Omitting this keyword has the same behavior as an empty array. + + +### dependentRequired + +The value of this keyword MUST be an object. Properties in +this object, if any, MUST be arrays. Elements in each array, +if any, MUST be strings, and MUST be unique. + +This keyword specifies properties that are required if a specific +other property is present. Their requirement is dependent on the +presence of the other property. + +Validation succeeds if, for each name that appears in both +the instance and as a name within this keyword's value, every +item in the corresponding array is also the name of a property +in the instance. + +Omitting this keyword has the same behavior as an empty object. + + + + +# Vocabularies for Semantic Content With "format" {#format} + +## Foreword + +Structural validation alone may be insufficient to allow an application to +correctly +utilize certain values. The "format" annotation keyword is defined to allow +schema +authors to convey semantic information for a fixed subset of values which +are +accurately described by authoritative resources, be they RFCs or other external +specifications. + +The value of this keyword is called a format attribute. It MUST be a string. +A +format attribute can generally only validate a given set of instance types. +If +the type of the instance to validate is not in this set, validation for this +format attribute and instance SHOULD succeed. All format attributes defined +in this section apply to strings, but a format attribute can be specified +to apply to any instance types defined in the data model defined in the +[core JSON Schema.](#json-schema) [^CREF1] + +[^CREF1]: Note that the "type" keyword in this specification defines an "integer" type + which is not part of the data model. Therefore a format attribute can be + limited to numbers, but not specifically to integers. However, a numeric + format can be used alongside the "type" keyword with a value of "integer", + or could be explicitly defined to always pass if the number is not an integer, + which produces essentially the same behavior as only applying to integers. + + +The current IRI for this vocabulary, known as the Format-Annotation vocabulary, +is: +\. The current +IRI for the corresponding meta-schema is: [](https://json-schema.org/draft/next/meta/format-annotation). +Implementing support for this vocabulary is REQUIRED. + +In addition to the Format-Annotation vocabulary, a secondary vocabulary is +available +for custom meta-schemas that defines "format" as an assertion. The IRI for +the +Format-Assertion vocabulary, is: +\. The current +IRI for the corresponding meta-schema is: [](https://json-schema.org/draft/next/meta/format-assertion). +Implementing support for the Format-Assertion vocabulary is OPTIONAL. + +Specifying both the Format-Annotation and the Format-Assertion vocabularies +is functionally +equivalent to specifying only the Format-Assertion vocabulary since its requirements +are a superset of the Format-Annotation vocabulary. + + +## Implementation Requirements + +The "format" keyword functions as defined by the vocabulary which is referenced. + +### Format-Annotation Vocabulary + +The value of format MUST be collected as an annotation, if the implementation +supports annotation collection. This enables application-level validation +when +schema validation is unavailable or inadequate. + +Implementations MAY still treat "format" as an assertion in addition to an +annotation and attempt to validate the value's conformance to the specified +semantics. The implementation MUST provide options to enable and disable +such +evaluation and MUST be disabled by default. Implementations SHOULD document +their level of support for such validation.[^CREF2] + +[^CREF2]: Specifying the Format-Annotation vocabulary and enabling validation in an + implementation should not be viewed as being equivalent to specifying + the Format-Assertion vocabulary since implementations are not required to + provide full validation support when the Format-Assertion vocabulary + is not specified. + + +When the implementation is configured for assertion behavior, it: + +> > SHOULD provide an implementation-specific best effort validation +> for each format attribute defined below; + +> > MAY choose to implement validation of any or all format attributes +> as a no-op by always producing a validation result of true; + + +[^CREF3] + +[^CREF3]: This matches the current reality of implementations, which provide + widely varying levels of validation, including no validation at all, + for some or all format attributes. It is also designed to encourage + relying only on the annotation behavior and performing semantic + validation in the application, which is the recommended best practice. + + + +### Format-Assertion Vocabulary + +When the Format-Assertion vocabulary is declared with a value of true, +implementations MUST provide full validation support for all of the formats +defined by this specificaion. Implementations that cannot provide full +validation support MUST refuse to process the schema. + +An implementation that supports the Format-Assertion vocabulary: + +> > MUST still collect "format" as an annotation if the implementation +> > supports annotation collection; + +> > MUST evaluate "format" as an assertion; + +> > MUST implement syntactic validation for all format attributes defined +> in this specification, and for any additional format attributes that +> it recognizes, such that there exist possible instance values +> of the correct type that will fail validation. + + +The requirement for minimal validation of format attributes is intentionally +vague and permissive, due to the complexity involved in many of the attributes. +Note in particular that the requirement is limited to syntactic checking; +it is +not to be expected that an implementation would send an email, attempt to +connect +to a URL, or otherwise check the existence of an entity identified by a format +instance.[^CREF4] + +[^CREF4]: The expectation is that for simple formats such as date-time, syntactic + validation will be thorough. For a complex format such as email addresses, + which are the amalgamation of various standards and numerous adjustments + over time, with obscure and/or obsolete rules that may or may not be + restricted by other applications making use of the value, a minimal validation + is sufficient. For example, an instance string that does not contain + an "@" is clearly not a valid email address, and an "email" or "hostname" + containing characters outside of 7-bit ASCII is likewise clearly invalid. + + +It is RECOMMENDED that implementations use a common parsing library for each +format, +or a well-known regular expression. Implementations SHOULD clearly document +how and to what degree each format attribute is validated. + +The [standard core and validation meta-schema](#meta-schema) includes this +vocabulary in its "$vocabulary" keyword with a value of false, +since by default implementations are not required to support this keyword +as an assertion. Supporting the format vocabulary with a value of true is +understood to greatly increase code size and in some cases execution time, +and will not be appropriate for all implementations. + + +### Custom format attributes + +Implementations MAY support custom format attributes. Save for agreement +between +parties, schema authors SHALL NOT expect a peer implementation to support +such +custom format attributes. An implementation MUST NOT fail to collect unknown +formats +as annotations. When the Format-Assertion vocabulary is specified, implementations +MUST fail upon encountering unknown formats. + +Vocabularies do not support specifically declaring different value sets for +keywords. +Due to this limitation, and the historically uneven implementation of this +keyword, +it is RECOMMENDED to define additional keywords in a custom vocabulary rather +than +additional format attributes if interoperability is desired. + + + +## Defined Formats + +### Dates, Times, and Duration + +These attributes apply to string instances. + +Date and time format names are derived from [RFC 3339, section 5.6](#RFC3339). +The duration format is from the ISO 8601 ABNF as given +in Appendix A of RFC 3339. + +Implementations supporting formats SHOULD implement support for +the following attributes: + +date-time: +: A string instance is valid against this attribute if it is + a valid representation according to the "date-time' ABNF rule + (referenced above) + + +date: +: A string instance is valid against this attribute if it is + a valid representation according to the "full-date" ABNF rule + (referenced above) + + +time: +: A string instance is valid against this attribute if it is + a valid representation according to the "full-time" ABNF rule + (referenced above) + + +duration: +: A string instance is valid against this attribute if it is + a valid representation according to the "duration" ABNF rule + (referenced above) + + +Implementations MAY support additional attributes using the other +format names defined anywhere in that RFC. If "full-date" or "full-time" +are implemented, the corresponding short form ("date" or "time" +respectively) MUST be implemented, and MUST behave identically. +Implementations SHOULD NOT define extension attributes +with any name matching an RFC 3339 format unless it validates +according to the rules of that format.[^CREF5] + +[^CREF5]: There is not currently consensus on the need for supporting + all RFC 3339 formats, so this approach of reserving the + namespace will encourage experimentation without committing + to the entire set. Either the format implementation requirements + will become more flexible in general, or these will likely + either be promoted to fully specified attributes or dropped. + + + +### Email Addresses + +These attributes apply to string instances. + +A string instance is valid against these attributes if it is a valid +Internet email address as follows: + +email: +: As defined by the "Mailbox" ABNF rule in [RFC 5321, section 4.1.2](#RFC5321). + + +idn-email: +: As defined by the extended "Mailbox" ABNF rule in [RFC 6531, section 3.3](#RFC6531). + +Note that all strings valid against the "email" attribute are also +valid against the "idn-email" attribute. + + +### Hostnames + +These attributes apply to string instances. + +A string instance is valid against these attributes if it is a valid +representation for an Internet hostname as follows: + +hostname: +: As defined by [RFC 1123, section 2.1](#RFC1123), + including host names produced using the Punycode algorithm + specified in [RFC 5891, section 4.4](#RFC5891). + + +idn-hostname: +: As defined by either RFC 1123 as for hostname, or an + internationalized hostname as defined by [RFC 5890, section 2.3.2.3](#RFC5890). + +Note that all strings valid against the "hostname" attribute are also +valid against the "idn-hostname" attribute. + + +### IP Addresses + +These attributes apply to string instances. + +A string instance is valid against these attributes if it is a valid +representation of an IP address as follows: + +ipv4: +: An IPv4 address according to the "dotted-quad" ABNF + syntax as defined in [RFC 2673, section 3.2](#RFC2673). + + +ipv6: +: An IPv6 address as defined in [RFC 4291, section 2.2](#RFC4291). + + + +### Resource Identifiers + +These attributes apply to string instances. + + + +uri: +: A string instance is valid against this attribute if it is + a valid IRI, according to {{RFC3987}}. + + +uri-reference: +: A string instance is valid against this attribute if it is a valid URI + Reference (either a URI or a relative-reference), + according to {{RFC3986}}. + + +iri: +: A string instance is valid against this attribute if it is + a valid IRI, according to {{RFC3987}}. + + +iri-reference: +: A string instance is valid against this attribute if it is a valid IRI + Reference (either an IRI or a relative-reference), + according to {{RFC3987}}. + + +uuid: +: A string instance is valid against this attribute if it is a valid + string representation of a UUID, according to {{RFC4122}}. + + +Note that all valid URIs are valid IRIs, and all valid URI References are +also valid IRI References. + +Note also that the "uuid" format is for plain UUIDs, not UUIDs in URNs. +An example +is "f81d4fae-7dec-11d0-a765-00a0c91e6bf6". For UUIDs as URNs, use the "uri" +format, +with a "pattern" regular expression of "^urn:uuid:" to indicate the URI scheme +and +URN namespace. + + +### uri-template + +This attribute applies to string instances. + +A string instance is valid against this attribute if it is a valid URI Template +(of any level), according to {{RFC6570}}. + +Note that URI Templates may be used for IRIs; there is no separate +IRI Template specification. + + +### JSON Pointers + +These attributes apply to string instances. + + + +json-pointer: +: A string instance is valid against this attribute if it + is a valid JSON string representation of a JSON Pointer, + according to [RFC 6901, section 5](#RFC6901). + + +relative-json-pointer: +: A string instance is valid against this attribute if it is a valid +[Relative JSON Pointer](#relative-json-pointer). + +To allow for both absolute and relative JSON Pointers, use "anyOf" or +"oneOf" to indicate support for either format. + + +### regex + +This attribute applies to string instances. + +A regular expression, which SHOULD be valid according to the +[ECMA-262](#ecma262) regular expression dialect. + +Implementations that validate formats MUST accept at least the subset of +ECMA-262 defined in the [Regular Expressions](#regexInterop) section of +this specification, and SHOULD accept all valid ECMA-262 expressions. + + + + +# A Vocabulary for the Contents of String-Encoded Data {#content} + +## Foreword + +Annotations defined in this section indicate that an instance contains +non-JSON data encoded in a JSON string. + +These properties provide additional information required to interpret JSON +data +as rich multimedia documents. They describe the type of content, how it +is encoded, +and/or how it may be validated. They do not function as validation assertions; +a malformed string-encoded document MUST NOT cause the containing instance +to be considered invalid. + +Meta-schemas that do not use "$vocabulary" SHOULD be considered to +require this vocabulary as if its IRI were present with a value of true. + +The current IRI for this vocabulary, known as the Content vocabulary, is: +\. + +The current IRI for the corresponding meta-schema is: +[](https://json-schema.org/draft/next/meta/content). + + +## Implementation Requirements + +Due to security and performance concerns, as well as the open-ended nature +of +possible content types, implementations MUST NOT automatically decode, parse, +and/or validate the string contents. Applications are expected to use these +annotations to invoke the appropriate libraries separately. + +All keywords in this section apply only to strings, and have no +effect on other data types. + + +## contentEncoding + +If the instance value is a string, this property defines that the string +SHOULD be interpreted as encoded binary data and applications wishing +to decode it SHOULD do so using the encoding named by this property. + +Possible values indicating base 16, 32, and 64 encodings with several +variations are listed in [RFC 4648](#RFC4648). Additionally, +sections 6.7 and 6.8 of [RFC 2045](#RFC2045) provide +encodings used in MIME. This keyword is derived from MIME's +Content-Transfer-Encoding header, which was designed to map binary data +into ASCII characters. It is not related to HTTP's Content-Encoding header, +which is used to encode (e.g. compress or encrypt) +the content of HTTP request and responses. + +As "base64" is defined in both RFCs, the definition +from RFC 4648 SHOULD be assumed unless the string is specifically intended +for use in a MIME context. Note that all of these encodings result in +strings consisting only of 7-bit ASCII characters. Therefore, this keyword +has no meaning for strings containing characters outside of that range. + +If this keyword is absent, but "contentMediaType" is present, this +indicates that the encoding is the identity encoding, meaning that +no transformation was needed in order to represent the content in +a UTF-8 string. + +The value of this property MUST be a string. + + +## contentMediaType + +If the instance is a string, this property indicates the media type +of the contents of the string. If "contentEncoding" is present, +this property describes the decoded string. + +The value of this property MUST be a string, which MUST be a media type, +as defined by [RFC 2046](#RFC2046). + + +## contentSchema + +If the instance is a string, and if "contentMediaType" is present, this +property contains a schema which describes the structure of the string. + +This keyword MAY be used with any media type that can be mapped into +JSON Schema's data model. Specifying such mappings is outside of the +scope of this specification. + +The value of this property MUST be a valid JSON schema. It SHOULD be ignored +if +"contentMediaType" is not present. Accessing the schema through the schema +location +IRI included as part of the annotation will ensure that it is correctly processed +as a subschema. Using the extracted annotation value directly is only safe +if +the schema is an embedded resource with both "$schema" and an absolute-IRI +"$id". + + +## Example + +Here is an example schema, illustrating the use of "contentEncoding" and +"contentMediaType": + +~~~~ +{ + "type": "string", + "contentEncoding": "base64", + "contentMediaType": "image/png" +} + +~~~~ + +Instances described by this schema are expected to be strings, +and their values should be interpretable as base64-encoded PNG images. + +Another example: + +~~~~ +{ + "type": "string", + "contentMediaType": "text/html" +} + +~~~~ + +Instances described by this schema are expected to be strings containing +HTML, +using whatever character set the JSON string was decoded into. +Per section 8.1 of [RFC 8259](#RFC8259), outside of an entirely closed +system, this MUST be UTF-8. + +This example describes a JWT that is MACed using the HMAC SHA-256 +algorithm, and requires the "iss" and "exp" fields in its claim set. + +~~~~ +{ + "type": "string", + "contentMediaType": "application/jwt", + "contentSchema": { + "type": "array", + "minItems": 2, + "prefixItems": [ + { + "const": { + "typ": "JWT", + "alg": "HS256" + } + }, + { + "type": "object", + "required": ["iss", "exp"], + "properties": { + "iss": {"type": "string"}, + "exp": {"type": "integer"} + } + } + ] + } +} +~~~~ + +Note that "contentEncoding" does not appear. While the "application/jwt" +media type makes use of base64url encoding, that is defined by the media +type, which determines how the JWT string is decoded into a list of two +JSON data structures: first the header, and then the payload. Since the +JWT media type ensures that the JWT can be represented in a JSON string, +there is no need for further encoding or decoding. + + + +# A Vocabulary for Basic Meta-Data Annotations + +These general-purpose annotation keywords provide commonly used information +for documentation and user interface display purposes. They are not intended +to form a comprehensive set of features. Rather, additional vocabularies +can be defined for more complex annotation-based applications. + +Meta-schemas that do not use "$vocabulary" SHOULD be considered to +require this vocabulary as if its IRI were present with a value of true. + +The current IRI for this vocabulary, known as the Meta-Data vocabulary, is: +\. + +The current IRI for the corresponding meta-schema is: +[](https://json-schema.org/draft/next/meta/meta-data). + +## "title" and "description" + +The value of both of these keywords MUST be a string. + +Both of these keywords can be used to decorate a user interface with +information about the data produced by this user interface. A title will +preferably be short, whereas a description will provide explanation about +the purpose of the instance described by this schema. + + +## "default" + +There are no restrictions placed on the value of this keyword. When +multiple occurrences of this keyword are applicable to a single +sub-instance, implementations SHOULD remove duplicates. + +This keyword can be used to supply a default JSON value associated with a +particular schema. It is RECOMMENDED that a default value be valid against +the associated schema. + + +## "deprecated" + +The value of this keyword MUST be a boolean. When multiple occurrences +of this keyword are applicable to a single sub-instance, applications +SHOULD consider the instance location to be deprecated if any occurrence +specifies a true value. + +If "deprecated" has a value of boolean true, it indicates that applications +SHOULD refrain from usage of the declared property. It MAY mean the property +is going to be removed in the future. + +A root schema containing "deprecated" with a value of true indicates that +the entire resource being described MAY be removed in the future. + +The "deprecated" keyword applies to each instance location to which the +schema object containing the keyword successfully applies. This can +result in scenarios where every array item or object property +is deprecated even though the containing array or object is not. + +Omitting this keyword has the same behavior as a value of false. + + +## "readOnly" and "writeOnly" + +The value of these keywords MUST be a boolean. When multiple occurrences +of these keywords are applicable to a single sub-instance, the resulting +behavior SHOULD be as for a true value if any occurrence specifies a true +value, +and SHOULD be as for a false value otherwise. + +If "readOnly" has a value of boolean true, it indicates that the value +of the instance is managed exclusively by the owning authority, and +attempts by an application to modify the value of this property are +expected to be ignored or rejected by that owning authority. + +An instance document that is marked as "readOnly" for the entire document +MAY be ignored if sent to the owning authority, or MAY result in an +error, at the authority's discretion. + +If "writeOnly" has a value of boolean true, it indicates that the value +is never present when the instance is retrieved from the owning authority. +It can be present when sent to the owning authority to update or create +the document (or the resource it represents), but it will not be included +in any updated or newly created version of the instance. + +An instance document that is marked as "writeOnly" for the entire document +MAY be returned as a blank document of some sort, or MAY produce an error +upon retrieval, or have the retrieval request ignored, at the authority's +discretion. + +For example, "readOnly" would be used to mark a database-generated serial +number as read-only, while "writeOnly" would be used to mark a password +input field. + +These keywords can be used to assist in user interface instance generation. +In particular, an application MAY choose to use a widget that hides +input values as they are typed for write-only fields. + +Omitting these keywords has the same behavior as values of false. + + +## "examples" + +The value of this keyword MUST be an array. +There are no restrictions placed on the values within the array. +When multiple occurrences of this keyword are applicable to a single +sub-instance, implementations MUST provide a flat array of all +values rather than an array of arrays. + +This keyword can be used to provide sample JSON values associated with a +particular schema, for the purpose of illustrating usage. It is +RECOMMENDED that these values be valid against the associated schema. + +Implementations MAY use the value(s) of "default", if present, as +an additional example. If "examples" is absent, "default" +MAY still be used in this manner. + + + +# Security Considerations {#security} + +JSON Schema validation defines a vocabulary for JSON Schema core and concerns +all +the security considerations listed there. + +JSON Schema validation allows the use of Regular Expressions, which have +numerous +different (often incompatible) implementations. +Some implementations allow the embedding of arbitrary code, which is outside +the +scope of JSON Schema and MUST NOT be permitted. +Regular expressions can often also be crafted to be extremely expensive to +compute +(with so-called "catastrophic backtracking"), resulting in a denial-of-service +attack. + +Implementations that support validating or otherwise evaluating instance +string data based on "contentEncoding" and/or "contentMediaType" are at +risk of evaluating data in an unsafe way based on misleading information. +Applications can mitigate this risk by only performing such processing +when a relationship between the schema and instance is established +(e.g., they share the same authority). + +Processing a media type or encoding is subject to the security considerations +of that media type or encoding. For example, the security considerations +of [RFC 4329 Scripting Media Types](#RFC4329) apply when +processing JavaScript or ECMAScript encoded within a JSON string. + + +--- back + +# Keywords Moved from Validation to Core + +Several keywords have been moved from this document into the +[Core Specification](#json-schema) starting with draft 2019-09, +in some cases with re-naming or other changes. This affects the following +former +validation keywords: + +"definitions" +: Renamed to "$defs" to match "$ref" and be shorter to type. + Schema vocabulary authors SHOULD NOT define a "definitions" keyword + with different behavior in order to avoid invalidating schemas that + still use the older name. While "definitions" is absent in the + single-vocabulary meta-schemas referenced by this document, it + remains present in the default meta-schema, and implementations + SHOULD assume that "$defs" and "definitions" have the same + behavior when that meta-schema is used. + + +"allOf", "anyOf", "oneOf", "not", "if", "then", "else", "items", +"additionalItems", "contains", "propertyNames", "properties", +"patternProperties", "additionalProperties" +: All of these keywords apply subschemas to the instance and combine + their results, without asserting any conditions of their own. + Without assertion keywords, these applicators can only cause assertion + failures by using the false boolean schema, or by inverting the result + of the true boolean schema (or equivalent schema objects). + For this reason, they are better defined as a generic mechanism on which + validation, hyper-schema, and extension vocabularies can all be based. + + +"maxContains", "minContains" +: These keywords modify the behavior of "contains", and are therefore + grouped with it in the applicator vocabulary. + + +"dependencies" +: This keyword had two different modes of behavior, which made it + relatively challenging to implement and reason about. + The schema form has been moved to Core and renamed to + "dependentSchemas", as part of the applicator vocabulary. + It is analogous to "properties", except that instead of applying + its subschema to the property value, it applies it to the object + containing the property. + The property name array form is retained here and renamed to + "dependentRequired", as it is an assertion which is a shortcut + for the conditional use of the "required" assertion keyword. + + + +# Acknowledgments + +Thanks to +Gary Court, +Francis Galiegue, +Kris Zyp, +and Geraint Luff +for their work on the initial drafts of JSON Schema. + +Thanks to +Jason Desrosiers, +Daniel Perrett, +Erik Wilde, +Evgeny Poberezkin, +Brad Bowman, +Gowry Sankar, +Donald Pipowitch, +Dave Finlay, +Denis Laxalde, +Phil Sturgeon, +Shawn Silverman, +and Karen Etheridge +for their submissions and patches to the document. + + +# ChangeLog + +[^CREF6] + +[^CREF6]: This section to be removed before leaving Internet-Draft status. + + + + +draft-next +: * Use IRIs instead of URIs + + + +draft-bhutton-json-schema-validation-01 +: * Improve and clarify the "minContains" keyword explanation + + * Remove the use of "production" in favour of "ABNF rule" + + + +draft-bhutton-json-schema-validation-00 +: * Correct email format RFC reference to 5321 instead of 5322 + + * Clarified the set and meaning of "contentEncoding" values + + * Reference ECMA-262, 11th edition for regular expression support + + * Split "format" into an annotation only vocabulary and an assertion vocabulary + + * Clarify "deprecated" when applicable to arrays + + + +draft-handrews-json-schema-validation-02 +: * Grouped keywords into formal vocabularies + + * Update "format" implementation requirements in terms of vocabularies + + * By default, "format" MUST NOT be validated, although validation can be enabled + + * A vocabulary declaration can be used to require "format" validation + + * Moved "definitions" to the core spec as "$defs" + + * Moved applicator keywords to the core spec + + * Renamed the array form of "dependencies" to "dependentRequired", moved the + schema form to the core spec + + * Specified all "content\*" keywords as annotations, not assertions + + * Added "contentSchema" to allow applying a schema to a string-encoded document + + * Also allow RFC 4648 encodings in "contentEncoding" + + * Added "minContains" and "maxContains" + + * Update RFC reference for "hostname" and "idn-hostname" + + * Add "uuid" and "duration" formats + + + +draft-handrews-json-schema-validation-01 +: * This draft is purely a clarification with no functional changes + + * Provided the general principle behind ignoring annotations under "not" and + similar cases + + * Clarified "if"/"then"/"else" validation interactions + + * Clarified "if"/"then"/"else" behavior for annotation + + * Minor formatting and cross-referencing improvements + + + +draft-handrews-json-schema-validation-00 +: * Added "if"/"then"/"else" + + * Classify keywords as assertions or annotations per the core spec + + * Warn of possibly removing "dependencies" in the future + + * Grouped validation keywords into sub-sections for readability + + * Moved "readOnly" from hyper-schema to validation meta-data + + * Added "writeOnly" + + * Added string-encoded media section, with former hyper-schema "media" keywords + + * Restored "regex" format (removal was unintentional) + + * Added "date" and "time" formats, and reserved additional RFC 3339 format + names + + * I18N formats: "iri", "iri-reference", "idn-hostname", "idn-email" + + * Clarify that "json-pointer" format means string encoding, not URI fragment + + * Fixed typo that inverted the meaning of "minimum" and "exclusiveMinimum" + + * Move format syntax references into Normative References + + * JSON is a normative requirement + + + +draft-wright-json-schema-validation-01 +: * Standardized on hyphenated format names with full words ("uriref" becomes + "uri-reference") + + * Add the formats "uri-template" and "json-pointer" + + * Changed "exclusiveMaximum"/"exclusiveMinimum" from boolean modifiers of "maximum"/"minimum" + to independent numeric fields. + + * Split the additionalItems/items into two sections + + * Reworked properties/patternProperties/additionalProperties definition + + * Added "examples" keyword + + * Added "contains" keyword + + * Allow empty "required" and "dependencies" arrays + + * Fixed "type" reference to primitive types + + * Added "const" keyword + + * Added "propertyNames" keyword + + + +draft-wright-json-schema-validation-00 +: * Added additional security considerations + + * Removed reference to "latest version" meta-schema, use numbered version instead + + * Rephrased many keyword definitions for brevity + + * Added "uriref" format that also allows relative URI references + + + +draft-fge-json-schema-validation-00 +: * Initial draft. + + * Salvaged from draft v3. + + * Redefine the "required" keyword. + + * Remove "extends", "disallow" + + * Add "anyOf", "allOf", "oneOf", "not", "definitions", "minProperties", + "maxProperties". + + * "dependencies" member values can no longer be single strings; at + least one element is required in a property dependency array. + + * Rename "divisibleBy" to "multipleOf". + + * "type" arrays can no longer have schemas; remove "any" as a possible + value. + + * Rework the "format" section; make support optional. + + * "format": remove attributes "phone", "style", "color"; rename + "ip-address" to "ipv4"; add references for all attributes. + + * Provide algorithms to calculate schema(s) for array/object + instances. + + * Add interoperability considerations. + + + diff --git a/jsonschema-validation.xml b/jsonschema-validation.xml deleted file mode 100644 index 63475c2c..00000000 --- a/jsonschema-validation.xml +++ /dev/null @@ -1,1497 +0,0 @@ - - - - - - - - - - - - - - - - - - - - -]> - - - - - - - - - - - - JSON Schema Validation: A Vocabulary for Structural Validation of JSON - - - -
- aaa@bzfx.net -
- - - -
- andrews_henry@yahoo.com -
- - - - Postman -
- ben@jsonschema.dev - https://jsonschema.dev -
- - - - Internet Engineering Task Force - JSON - Schema - validation - - - - JSON Schema (application/schema+json) has several purposes, one of which is JSON - instance validation. - This document specifies a vocabulary for JSON Schema to describe the meaning of JSON - documents, provide hints for user interfaces working with JSON data, and to make - assertions about what a valid document must look like. - - - - - - The issues list for this draft can be found at - . - - - For additional information, see . - - - To provide feedback, use this issue tracker, the communication methods listed on the - homepage, or email the document editors. - - - - - -
- - JSON Schema can be used to require that a given JSON document (an instance) - satisfies a certain number of criteria. These criteria are asserted by using - keywords described in this specification. In addition, a set of keywords - is also defined to assist in interactive user interface instance generation. - - - This specification will use the concepts, syntax, and terminology defined - by the JSON Schema core specification. - -
- -
- - - - The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", - "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be - interpreted as described in RFC 2119. - - - This specification uses the term "container instance" to refer to both array and - object instances. It uses the term "children instances" to refer to array elements - or object member values. - - - Elements in an array value are said to be unique if no two elements of this array - are equal. - -
- -
- - JSON Schema validation asserts constraints on the structure of instance data. - An instance location that satisfies all asserted constraints is then - annotated with any keywords that contain non-assertion information, - such as descriptive metadata and usage hints. If all locations within - the instance satisfy all asserted constraints, then the instance is - said to be valid against the schema. - - - Each schema object is independently evaluated against each instance location - to which it applies. This greatly simplifies the implementation requirements - for validators by ensuring that they do not need to maintain state across - the document-wide validation process. - - - This specification defines a set of assertion keywords, as well as a small vocabulary - of metadata keywords that can be used to annotate the JSON instance with - useful information. The keyword is intended primarily - as an annotation, but can optionally be used as an assertion. The - keywords are annotations for working with documents - embedded as JSON strings. - -
- -
- -
- - It should be noted that the nul character (\u0000) is valid in a JSON string. An - instance to validate may contain a string value with this character, regardless - of the ability of the underlying programming language to deal with such data. - -
- -
- - The JSON specification allows numbers with arbitrary precision, and JSON Schema - does not add any such bounds. - This means that numeric instances processed by JSON Schema can be arbitrarily large and/or - have an arbitrarily long decimal part, regardless of the ability of the - underlying programming language to deal with such data. - -
- -
- - Keywords that use regular expressions, or constrain the instance value - to be a regular expression, are subject to the interoperability - considerations for regular expressions in the - JSON Schema Core specification. - -
- -
- -
- - The current IRI for the default JSON Schema dialect meta-schema is - . - For schema author convenience, this meta-schema describes a dialect - consisting of all vocabularies - defined in this specification and the JSON Schema Core specification, - as well as two former keywords which are reserved for a transitional period. - Individual vocabulary and vocabulary meta-schema IRIs are given for - each section below. Certain vocabularies are optional to support, which - is explained in detail in the relevant sections. - - - Updated vocabulary and meta-schema IRIs MAY be published between - specification drafts in order to correct errors. Implementations - SHOULD consider IRIs dated after this specification draft and - before the next to indicate the same syntax and semantics - as those listed here. - -
- -
- - Validation keywords in a schema impose requirements for successful validation of an - instance. These keywords are all assertions without any annotation behavior. - - - Meta-schemas that do not use "$vocabulary" SHOULD be considered to - require this vocabulary as if its IRI were present with a value of true. - - - The current IRI for this vocabulary, known as the Validation vocabulary, is: - <https://json-schema.org/draft/next/vocab/validation>. - - - The current IRI for the corresponding meta-schema is: - . - - -
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- - The value of this keyword MUST be either a string or an array. If it is - an array, elements of the array MUST be strings and MUST be unique. - - - String values MUST be one of the six primitive types - ("null", "boolean", "object", "array", "number", or "string"), - or "integer" which matches any number with a zero fractional part. - - - If the value of "type" is a string, then an instance validates successfully if - its type matches the type represented by the value of the string. - - If the value of "type" is an array, then an instance validates successfully if - its type matches any of the types indicated by the strings in the array. - -
- -
- - The value of this keyword MUST be an array. This array SHOULD have at - least one element. Elements in the array SHOULD be unique. - - - An instance validates successfully against this keyword if its value is - equal to one of the elements in this keyword's array value. - - - Elements in the array might be of any type, including null. - -
- -
- - The value of this keyword MAY be of any type, including null. - - - Use of this keyword is functionally equivalent to an - "enum" with a single value. - - - An instance validates successfully against this keyword if its value is - equal to the value of the keyword. - -
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- -
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- - The value of "multipleOf" MUST be a number, strictly greater than 0. - - - A numeric instance is valid only if division by this keyword's value results in - an integer. - -
- -
- - The value of "maximum" MUST be a number, representing an inclusive upper limit - for a numeric instance. - - - If the instance is a number, then this keyword validates only if the instance is - less than or exactly equal to "maximum". - -
- -
- - The value of "exclusiveMaximum" MUST be a number, representing an exclusive upper - limit for a numeric instance. - - - If the instance is a number, then the instance is valid only if it has a value - strictly less than (not equal to) "exclusiveMaximum". - -
- -
- - The value of "minimum" MUST be a number, representing an inclusive lower limit - for a numeric instance. - - - If the instance is a number, then this keyword validates only if the instance is - greater than or exactly equal to "minimum". - -
- -
- - The value of "exclusiveMinimum" MUST be a number, representing an exclusive lower - limit for a numeric instance. - - - If the instance is a number, then the instance is valid only if it has a value - strictly greater than (not equal to) "exclusiveMinimum". - -
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- -
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- - The value of this keyword MUST be a non-negative integer. - - A string instance is valid against this keyword if its - length is less than, or equal to, the value of this keyword. - - - The length of a string instance is defined as the number of its - characters as defined by RFC 8259. - -
- -
- - The value of this keyword MUST be a non-negative integer. - - - A string instance is valid against this keyword if its - length is greater than, or equal to, the value of this keyword. - - - - The length of a string instance is defined as the number of its - characters as defined by RFC 8259. - - - Omitting this keyword has the same behavior as a value of 0. - -
- -
- - The value of this keyword MUST be a string. This string SHOULD be a - valid regular expression, according to the ECMA-262 regular expression - dialect. - - - A string instance is considered valid if the regular - expression matches the instance successfully. Recall: regular - expressions are not implicitly anchored. - -
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- -
- -
- - The value of this keyword MUST be a non-negative integer. - - - An array instance is valid against "maxItems" if its size is - less than, or equal to, the value of this keyword. - -
- -
- - The value of this keyword MUST be a non-negative integer. - - - An array instance is valid against "minItems" if its size is - greater than, or equal to, the value of this keyword. - - - Omitting this keyword has the same behavior as a value of 0. - -
- -
- - The value of this keyword MUST be a boolean. - - - If this keyword has boolean value false, the instance validates - successfully. If it has boolean value true, the instance validates - successfully if all of its elements are unique. - - - Omitting this keyword has the same behavior as a value of false. - -
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- -
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- - The value of this keyword MUST be a non-negative integer. - - - An object instance is valid against "maxProperties" if its - number of properties is less than, or equal to, the value of this - keyword. - -
- -
- - The value of this keyword MUST be a non-negative integer. - - - An object instance is valid against "minProperties" if its - number of properties is greater than, or equal to, the value of this - keyword. - - - Omitting this keyword has the same behavior as a value of 0. - -
- -
- - The value of this keyword MUST be an array. - Elements of this array, if any, MUST be strings, and MUST be unique. - - - An object instance is valid against this keyword if every item in the array is - the name of a property in the instance. - - - Omitting this keyword has the same behavior as an empty array. - -
- -
- - The value of this keyword MUST be an object. Properties in - this object, if any, MUST be arrays. Elements in each array, - if any, MUST be strings, and MUST be unique. - - - This keyword specifies properties that are required if a specific - other property is present. Their requirement is dependent on the - presence of the other property. - - - Validation succeeds if, for each name that appears in both - the instance and as a name within this keyword's value, every - item in the corresponding array is also the name of a property - in the instance. - - - Omitting this keyword has the same behavior as an empty object. - -
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- - Structural validation alone may be insufficient to allow an application to correctly - utilize certain values. The "format" annotation keyword is defined to allow schema - authors to convey semantic information for a fixed subset of values which are - accurately described by authoritative resources, be they RFCs or other external - specifications. - - - - The value of this keyword is called a format attribute. It MUST be a string. A - format attribute can generally only validate a given set of instance types. If - the type of the instance to validate is not in this set, validation for this - format attribute and instance SHOULD succeed. All format attributes defined - in this section apply to strings, but a format attribute can be specified - to apply to any instance types defined in the data model defined in the - core JSON Schema. - - Note that the "type" keyword in this specification defines an "integer" type - which is not part of the data model. Therefore a format attribute can be - limited to numbers, but not specifically to integers. However, a numeric - format can be used alongside the "type" keyword with a value of "integer", - or could be explicitly defined to always pass if the number is not an integer, - which produces essentially the same behavior as only applying to integers. - - - - - The current IRI for this vocabulary, known as the Format-Annotation vocabulary, is: - <https://json-schema.org/draft/next/vocab/format-annotation>. The current - IRI for the corresponding meta-schema is: - . - Implementing support for this vocabulary is REQUIRED. - - - In addition to the Format-Annotation vocabulary, a secondary vocabulary is available - for custom meta-schemas that defines "format" as an assertion. The IRI for the - Format-Assertion vocabulary, is: - <https://json-schema.org/draft/next/vocab/format-assertion>. The current - IRI for the corresponding meta-schema is: - . - Implementing support for the Format-Assertion vocabulary is OPTIONAL. - - - Specifying both the Format-Annotation and the Format-Assertion vocabularies is functionally - equivalent to specifying only the Format-Assertion vocabulary since its requirements - are a superset of the Format-Annotation vocabulary. - -
- -
- - The "format" keyword functions as defined by the vocabulary which is referenced. - - -
- - The value of format MUST be collected as an annotation, if the implementation - supports annotation collection. This enables application-level validation when - schema validation is unavailable or inadequate. - - - Implementations MAY still treat "format" as an assertion in addition to an - annotation and attempt to validate the value's conformance to the specified - semantics. The implementation MUST provide options to enable and disable such - evaluation and MUST be disabled by default. Implementations SHOULD document - their level of support for such validation. - - Specifying the Format-Annotation vocabulary and enabling validation in an - implementation should not be viewed as being equivalent to specifying - the Format-Assertion vocabulary since implementations are not required to - provide full validation support when the Format-Assertion vocabulary - is not specified. - - - - When the implementation is configured for assertion behavior, it: - - - SHOULD provide an implementation-specific best effort validation - for each format attribute defined below; - - - MAY choose to implement validation of any or all format attributes - as a no-op by always producing a validation result of true; - - - - This matches the current reality of implementations, which provide - widely varying levels of validation, including no validation at all, - for some or all format attributes. It is also designed to encourage - relying only on the annotation behavior and performing semantic - validation in the application, which is the recommended best practice. - - -
- -
- - When the Format-Assertion vocabulary is declared with a value of true, - implementations MUST provide full validation support for all of the formats - defined by this specificaion. Implementations that cannot provide full - validation support MUST refuse to process the schema. - - - An implementation that supports the Format-Assertion vocabulary: - - - MUST still collect "format" as an annotation if the implementation - supports annotation collection; - - - MUST evaluate "format" as an assertion; - - - MUST implement syntactic validation for all format attributes defined - in this specification, and for any additional format attributes that - it recognizes, such that there exist possible instance values - of the correct type that will fail validation. - - - The requirement for minimal validation of format attributes is intentionally - vague and permissive, due to the complexity involved in many of the attributes. - Note in particular that the requirement is limited to syntactic checking; it is - not to be expected that an implementation would send an email, attempt to connect - to a URL, or otherwise check the existence of an entity identified by a format - instance. - - The expectation is that for simple formats such as date-time, syntactic - validation will be thorough. For a complex format such as email addresses, - which are the amalgamation of various standards and numerous adjustments - over time, with obscure and/or obsolete rules that may or may not be - restricted by other applications making use of the value, a minimal validation - is sufficient. For example, an instance string that does not contain - an "@" is clearly not a valid email address, and an "email" or "hostname" - containing characters outside of 7-bit ASCII is likewise clearly invalid. - - - - It is RECOMMENDED that implementations use a common parsing library for each format, - or a well-known regular expression. Implementations SHOULD clearly document - how and to what degree each format attribute is validated. - - - The standard core and validation meta-schema - includes this vocabulary in its "$vocabulary" keyword with a value of false, - since by default implementations are not required to support this keyword - as an assertion. Supporting the format vocabulary with a value of true is - understood to greatly increase code size and in some cases execution time, - and will not be appropriate for all implementations. - -
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- - Implementations MAY support custom format attributes. Save for agreement between - parties, schema authors SHALL NOT expect a peer implementation to support such - custom format attributes. An implementation MUST NOT fail to collect unknown formats - as annotations. When the Format-Assertion vocabulary is specified, implementations - MUST fail upon encountering unknown formats. - - - Vocabularies do not support specifically declaring different value sets for keywords. - Due to this limitation, and the historically uneven implementation of this keyword, - it is RECOMMENDED to define additional keywords in a custom vocabulary rather than - additional format attributes if interoperability is desired. - -
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- -
- -
- - These attributes apply to string instances. - - - Date and time format names are derived from - RFC 3339, section 5.6. - The duration format is from the ISO 8601 ABNF as given - in Appendix A of RFC 3339. - - - Implementations supporting formats SHOULD implement support for - the following attributes: - - - A string instance is valid against this attribute if it is - a valid representation according to the "date-time' ABNF rule - (referenced above) - - - A string instance is valid against this attribute if it is - a valid representation according to the "full-date" ABNF rule - (referenced above) - - - A string instance is valid against this attribute if it is - a valid representation according to the "full-time" ABNF rule - (referenced above) - - - A string instance is valid against this attribute if it is - a valid representation according to the "duration" ABNF rule - (referenced above) - - - - - Implementations MAY support additional attributes using the other - format names defined anywhere in that RFC. If "full-date" or "full-time" - are implemented, the corresponding short form ("date" or "time" - respectively) MUST be implemented, and MUST behave identically. - Implementations SHOULD NOT define extension attributes - with any name matching an RFC 3339 format unless it validates - according to the rules of that format. - - There is not currently consensus on the need for supporting - all RFC 3339 formats, so this approach of reserving the - namespace will encourage experimentation without committing - to the entire set. Either the format implementation requirements - will become more flexible in general, or these will likely - either be promoted to fully specified attributes or dropped. - - -
- -
- - These attributes apply to string instances. - - - A string instance is valid against these attributes if it is a valid - Internet email address as follows: - - - As defined by the "Mailbox" ABNF rule in - RFC 5321, section 4.1.2. - - - As defined by the extended "Mailbox" ABNF rule in - RFC 6531, section 3.3. - - - Note that all strings valid against the "email" attribute are also - valid against the "idn-email" attribute. - -
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- - These attributes apply to string instances. - - - A string instance is valid against these attributes if it is a valid - representation for an Internet hostname as follows: - - - As defined by RFC 1123, section 2.1, - including host names produced using the Punycode algorithm - specified in RFC 5891, section 4.4. - - - As defined by either RFC 1123 as for hostname, or an - internationalized hostname as defined by - RFC 5890, section 2.3.2.3. - - - Note that all strings valid against the "hostname" attribute are also - valid against the "idn-hostname" attribute. - -
- -
- - These attributes apply to string instances. - - - A string instance is valid against these attributes if it is a valid - representation of an IP address as follows: - - - An IPv4 address according to the "dotted-quad" ABNF - syntax as defined in - RFC 2673, section 3.2. - - - An IPv6 address as defined in - RFC 4291, section 2.2. - - - -
- -
- - These attributes apply to string instances. - - - - - A string instance is valid against this attribute if it is - a valid IRI, according to . - - - A string instance is valid against this attribute if it is a valid URI - Reference (either a URI or a relative-reference), - according to . - - - A string instance is valid against this attribute if it is - a valid IRI, according to . - - - A string instance is valid against this attribute if it is a valid IRI - Reference (either an IRI or a relative-reference), - according to . - - - A string instance is valid against this attribute if it is a valid - string representation of a UUID, according to . - - - - - Note that all valid URIs are valid IRIs, and all valid URI References are - also valid IRI References. - - - Note also that the "uuid" format is for plain UUIDs, not UUIDs in URNs. An example - is "f81d4fae-7dec-11d0-a765-00a0c91e6bf6". For UUIDs as URNs, use the "uri" format, - with a "pattern" regular expression of "^urn:uuid:" to indicate the URI scheme and - URN namespace. - -
- -
- - This attribute applies to string instances. - - - A string instance is valid against this attribute if it is a valid URI Template - (of any level), according to . - - - Note that URI Templates may be used for IRIs; there is no separate - IRI Template specification. - -
- -
- - These attributes apply to string instances. - - - - - A string instance is valid against this attribute if it - is a valid JSON string representation of a JSON Pointer, - according to RFC 6901, section 5. - - - A string instance is valid against this attribute if it is a valid - Relative JSON Pointer. - - - To allow for both absolute and relative JSON Pointers, use "anyOf" or - "oneOf" to indicate support for either format. - -
-
- - This attribute applies to string instances. - - - A regular expression, which SHOULD be valid according to the - ECMA-262 regular expression dialect. - - - Implementations that validate formats MUST accept at least the subset of - ECMA-262 defined in the Regular Expressions - section of this specification, and SHOULD accept all valid ECMA-262 expressions. - -
-
-
- -
- -
- - Annotations defined in this section indicate that an instance contains - non-JSON data encoded in a JSON string. - - - These properties provide additional information required to interpret JSON data - as rich multimedia documents. They describe the type of content, how it is encoded, - and/or how it may be validated. They do not function as validation assertions; - a malformed string-encoded document MUST NOT cause the containing instance - to be considered invalid. - - - Meta-schemas that do not use "$vocabulary" SHOULD be considered to - require this vocabulary as if its IRI were present with a value of true. - - - The current IRI for this vocabulary, known as the Content vocabulary, is: - <https://json-schema.org/draft/next/vocab/content>. - - - The current IRI for the corresponding meta-schema is: - . - -
- -
- - Due to security and performance concerns, as well as the open-ended nature of - possible content types, implementations MUST NOT automatically decode, parse, - and/or validate the string contents. Applications are expected to use these - annotations to invoke the appropriate libraries separately. - - - All keywords in this section apply only to strings, and have no - effect on other data types. - -
- -
- - - If the instance value is a string, this property defines that the string - SHOULD be interpreted as encoded binary data and applications wishing - to decode it SHOULD do so using the encoding named by this property. - - - - Possible values indicating base 16, 32, and 64 encodings with several - variations are listed in RFC 4648. Additionally, - sections 6.7 and 6.8 of RFC 2045 provide - encodings used in MIME. This keyword is derived from MIME's - Content-Transfer-Encoding header, which was designed to map binary data - into ASCII characters. It is not related to HTTP's Content-Encoding header, - which is used to encode (e.g. compress or encrypt) - the content of HTTP request and responses. - - - As "base64" is defined in both RFCs, the definition - from RFC 4648 SHOULD be assumed unless the string is specifically intended - for use in a MIME context. Note that all of these encodings result in - strings consisting only of 7-bit ASCII characters. Therefore, this keyword - has no meaning for strings containing characters outside of that range. - - - - If this keyword is absent, but "contentMediaType" is present, this - indicates that the encoding is the identity encoding, meaning that - no transformation was needed in order to represent the content in - a UTF-8 string. - - - - The value of this property MUST be a string. - -
- -
- - If the instance is a string, this property indicates the media type - of the contents of the string. If "contentEncoding" is present, - this property describes the decoded string. - - - The value of this property MUST be a string, which MUST be a media type, - as defined by RFC 2046. - -
- -
- - If the instance is a string, and if "contentMediaType" is present, this - property contains a schema which describes the structure of the string. - - - This keyword MAY be used with any media type that can be mapped into - JSON Schema's data model. Specifying such mappings is outside of the - scope of this specification. - - - The value of this property MUST be a valid JSON schema. It SHOULD be ignored if - "contentMediaType" is not present. Accessing the schema through the schema location - IRI included as part of the annotation will ensure that it is correctly processed - as a subschema. Using the extracted annotation value directly is only safe if - the schema is an embedded resource with both "$schema" and an absolute-IRI "$id". - -
- -
-
- - Here is an example schema, illustrating the use of "contentEncoding" and - "contentMediaType": - - - - - - Instances described by this schema are expected to be strings, - and their values should be interpretable as base64-encoded PNG images. - -
- -
- - Another example: - - - - - - Instances described by this schema are expected to be strings containing HTML, - using whatever character set the JSON string was decoded into. - Per section 8.1 of - RFC 8259, outside of an entirely closed - system, this MUST be UTF-8. - -
- -
- - This example describes a JWT that is MACed using the HMAC SHA-256 - algorithm, and requires the "iss" and "exp" fields in its claim set. - - - - - - Note that "contentEncoding" does not appear. While the "application/jwt" - media type makes use of base64url encoding, that is defined by the media - type, which determines how the JWT string is decoded into a list of two - JSON data structures: first the header, and then the payload. Since the - JWT media type ensures that the JWT can be represented in a JSON string, - there is no need for further encoding or decoding. - -
-
- -
- -
- - These general-purpose annotation keywords provide commonly used information - for documentation and user interface display purposes. They are not intended - to form a comprehensive set of features. Rather, additional vocabularies - can be defined for more complex annotation-based applications. - - - Meta-schemas that do not use "$vocabulary" SHOULD be considered to - require this vocabulary as if its IRI were present with a value of true. - - - The current IRI for this vocabulary, known as the Meta-Data vocabulary, is: - <https://json-schema.org/draft/next/vocab/meta-data>. - - - The current IRI for the corresponding meta-schema is: - . - - -
- - The value of both of these keywords MUST be a string. - - - Both of these keywords can be used to decorate a user interface with - information about the data produced by this user interface. A title will - preferably be short, whereas a description will provide explanation about - the purpose of the instance described by this schema. - -
- -
- - There are no restrictions placed on the value of this keyword. When - multiple occurrences of this keyword are applicable to a single - sub-instance, implementations SHOULD remove duplicates. - - - This keyword can be used to supply a default JSON value associated with a - particular schema. It is RECOMMENDED that a default value be valid against - the associated schema. - -
- -
- - The value of this keyword MUST be a boolean. When multiple occurrences - of this keyword are applicable to a single sub-instance, applications - SHOULD consider the instance location to be deprecated if any occurrence - specifies a true value. - - - If "deprecated" has a value of boolean true, it indicates that applications - SHOULD refrain from usage of the declared property. It MAY mean the property - is going to be removed in the future. - - - A root schema containing "deprecated" with a value of true indicates that - the entire resource being described MAY be removed in the future. - - - The "deprecated" keyword applies to each instance location to which the - schema object containing the keyword successfully applies. This can - result in scenarios where every array item or object property - is deprecated even though the containing array or object is not. - - - Omitting this keyword has the same behavior as a value of false. - -
- -
- - The value of these keywords MUST be a boolean. When multiple occurrences - of these keywords are applicable to a single sub-instance, the resulting - behavior SHOULD be as for a true value if any occurrence specifies a true value, - and SHOULD be as for a false value otherwise. - - - If "readOnly" has a value of boolean true, it indicates that the value - of the instance is managed exclusively by the owning authority, and - attempts by an application to modify the value of this property are - expected to be ignored or rejected by that owning authority. - - - An instance document that is marked as "readOnly" for the entire document - MAY be ignored if sent to the owning authority, or MAY result in an - error, at the authority's discretion. - - - If "writeOnly" has a value of boolean true, it indicates that the value - is never present when the instance is retrieved from the owning authority. - It can be present when sent to the owning authority to update or create - the document (or the resource it represents), but it will not be included - in any updated or newly created version of the instance. - - - An instance document that is marked as "writeOnly" for the entire document - MAY be returned as a blank document of some sort, or MAY produce an error - upon retrieval, or have the retrieval request ignored, at the authority's - discretion. - - - For example, "readOnly" would be used to mark a database-generated serial - number as read-only, while "writeOnly" would be used to mark a password - input field. - - - These keywords can be used to assist in user interface instance generation. - In particular, an application MAY choose to use a widget that hides - input values as they are typed for write-only fields. - - - Omitting these keywords has the same behavior as values of false. - -
- -
- - The value of this keyword MUST be an array. - There are no restrictions placed on the values within the array. - When multiple occurrences of this keyword are applicable to a single - sub-instance, implementations MUST provide a flat array of all - values rather than an array of arrays. - - - This keyword can be used to provide sample JSON values associated with a - particular schema, for the purpose of illustrating usage. It is - RECOMMENDED that these values be valid against the associated schema. - - - Implementations MAY use the value(s) of "default", if present, as - an additional example. If "examples" is absent, "default" - MAY still be used in this manner. - -
-
- -
- - JSON Schema validation defines a vocabulary for JSON Schema core and concerns all - the security considerations listed there. - - - JSON Schema validation allows the use of Regular Expressions, which have numerous - different (often incompatible) implementations. - Some implementations allow the embedding of arbitrary code, which is outside the - scope of JSON Schema and MUST NOT be permitted. - Regular expressions can often also be crafted to be extremely expensive to compute - (with so-called "catastrophic backtracking"), resulting in a denial-of-service - attack. - - - Implementations that support validating or otherwise evaluating instance - string data based on "contentEncoding" and/or "contentMediaType" are at - risk of evaluating data in an unsafe way based on misleading information. - Applications can mitigate this risk by only performing such processing - when a relationship between the schema and instance is established - (e.g., they share the same authority). - - - Processing a media type or encoding is subject to the security considerations - of that media type or encoding. For example, the security considerations - of RFC 4329 Scripting Media Types apply when - processing JavaScript or ECMAScript encoded within a JSON string. - -
- - - - - - - - &RFC2119; - &RFC1123; - &RFC2045; - &RFC2046; - &RFC2673; - &RFC3339; - &RFC3986; - &RFC3987; - &RFC4122; - &RFC4291; - &RFC4648; - &RFC5321; - &RFC5890; - &RFC5891; - &RFC6570; - &RFC6531; - &RFC6901; - &RFC8259; - - - ECMA-262, 11th edition specification - - - - - - - Relative JSON Pointers - - - - - Cloudflare, Inc. - - - - - - - - - - JSON Schema: A Media Type for Describing JSON Documents - - - - - - - - - - - - - - - - - - - - &RFC4329; - - -
- - Several keywords have been moved from this document into the - Core Specification starting with draft 2019-09, - in some cases with re-naming or other changes. This affects the following former - validation keywords: - - - Renamed to "$defs" to match "$ref" and be shorter to type. - Schema vocabulary authors SHOULD NOT define a "definitions" keyword - with different behavior in order to avoid invalidating schemas that - still use the older name. While "definitions" is absent in the - single-vocabulary meta-schemas referenced by this document, it - remains present in the default meta-schema, and implementations - SHOULD assume that "$defs" and "definitions" have the same - behavior when that meta-schema is used. - - - All of these keywords apply subschemas to the instance and combine - their results, without asserting any conditions of their own. - Without assertion keywords, these applicators can only cause assertion - failures by using the false boolean schema, or by inverting the result - of the true boolean schema (or equivalent schema objects). - For this reason, they are better defined as a generic mechanism on which - validation, hyper-schema, and extension vocabularies can all be based. - - - These keywords modify the behavior of "contains", and are therefore - grouped with it in the applicator vocabulary. - - - This keyword had two different modes of behavior, which made it - relatively challenging to implement and reason about. - The schema form has been moved to Core and renamed to - "dependentSchemas", as part of the applicator vocabulary. - It is analogous to "properties", except that instead of applying - its subschema to the property value, it applies it to the object - containing the property. - The property name array form is retained here and renamed to - "dependentRequired", as it is an assertion which is a shortcut - for the conditional use of the "required" assertion keyword. - - - -
- -
- - Thanks to - Gary Court, - Francis Galiegue, - Kris Zyp, - and Geraint Luff - for their work on the initial drafts of JSON Schema. - - - Thanks to - Jason Desrosiers, - Daniel Perrett, - Erik Wilde, - Evgeny Poberezkin, - Brad Bowman, - Gowry Sankar, - Donald Pipowitch, - Dave Finlay, - Denis Laxalde, - Phil Sturgeon, - Shawn Silverman, - and Karen Etheridge - for their submissions and patches to the document. - -
- -
- - This section to be removed before leaving Internet-Draft status. - - - - - - Use IRIs instead of URIs - - - - - Improve and clarify the "minContains" keyword explanation - Remove the use of "production" in favour of "ABNF rule" - - - - - Correct email format RFC reference to 5321 instead of 5322 - Clarified the set and meaning of "contentEncoding" values - Reference ECMA-262, 11th edition for regular expression support - Split "format" into an annotation only vocabulary and an assertion vocabulary - Clarify "deprecated" when applicable to arrays - - - - - Grouped keywords into formal vocabularies - Update "format" implementation requirements in terms of vocabularies - By default, "format" MUST NOT be validated, although validation can be enabled - A vocabulary declaration can be used to require "format" validation - Moved "definitions" to the core spec as "$defs" - Moved applicator keywords to the core spec - Renamed the array form of "dependencies" to "dependentRequired", moved the schema form to the core spec - Specified all "content*" keywords as annotations, not assertions - Added "contentSchema" to allow applying a schema to a string-encoded document - Also allow RFC 4648 encodings in "contentEncoding" - Added "minContains" and "maxContains" - Update RFC reference for "hostname" and "idn-hostname" - Add "uuid" and "duration" formats - - - - - This draft is purely a clarification with no functional changes - Provided the general principle behind ignoring annotations under "not" and similar cases - Clarified "if"/"then"/"else" validation interactions - Clarified "if"/"then"/"else" behavior for annotation - Minor formatting and cross-referencing improvements - - - - - Added "if"/"then"/"else" - Classify keywords as assertions or annotations per the core spec - Warn of possibly removing "dependencies" in the future - Grouped validation keywords into sub-sections for readability - Moved "readOnly" from hyper-schema to validation meta-data - Added "writeOnly" - Added string-encoded media section, with former hyper-schema "media" keywords - Restored "regex" format (removal was unintentional) - Added "date" and "time" formats, and reserved additional RFC 3339 format names - I18N formats: "iri", "iri-reference", "idn-hostname", "idn-email" - Clarify that "json-pointer" format means string encoding, not URI fragment - Fixed typo that inverted the meaning of "minimum" and "exclusiveMinimum" - Move format syntax references into Normative References - JSON is a normative requirement - - - - - Standardized on hyphenated format names with full words ("uriref" becomes "uri-reference") - Add the formats "uri-template" and "json-pointer" - Changed "exclusiveMaximum"/"exclusiveMinimum" from boolean modifiers of "maximum"/"minimum" to independent numeric fields. - Split the additionalItems/items into two sections - Reworked properties/patternProperties/additionalProperties definition - Added "examples" keyword - Added "contains" keyword - Allow empty "required" and "dependencies" arrays - Fixed "type" reference to primitive types - Added "const" keyword - Added "propertyNames" keyword - - - - - Added additional security considerations - Removed reference to "latest version" meta-schema, use numbered version instead - Rephrased many keyword definitions for brevity - Added "uriref" format that also allows relative URI references - - - - - Initial draft. - Salvaged from draft v3. - Redefine the "required" keyword. - Remove "extends", "disallow" - Add "anyOf", "allOf", "oneOf", "not", "definitions", "minProperties", - "maxProperties". - "dependencies" member values can no longer be single strings; at - least one element is required in a property dependency array. - Rename "divisibleBy" to "multipleOf". - "type" arrays can no longer have schemas; remove "any" as a possible - value. - Rework the "format" section; make support optional. - "format": remove attributes "phone", "style", "color"; rename - "ip-address" to "ipv4"; add references for all attributes. - Provide algorithms to calculate schema(s) for array/object - instances. - Add interoperability considerations. - - - - -
- - diff --git a/relative-json-pointer.md b/relative-json-pointer.md new file mode 100644 index 00000000..62beab19 --- /dev/null +++ b/relative-json-pointer.md @@ -0,0 +1,280 @@ +--- +v: 3 +docname: draft-handrews-relative-json-pointer-03 +cat: info +submissiontype: IETF +title: Relative JSON Pointers +abbrev: Relative JSON Pointers +wg: Internet Engineering Task Force +kw: JSON +date: 2023 +author: +- ins: G. Luff + name: Geraint Luff + org: '' + city: Cambridge + country: UK + email: luffgd@gmail.com +- role: editor + ins: H. Andrews + name: Henry Andrews + org: '' + email: andrews_henry@yahoo.com +- role: editor + ins: B. Hutton + name: Ben Hutton + org: '' + email: ben@jsonschema.dev + uri: https://jsonschema.dev +normative: + RFC6901: +informative: + RFC8259: + +--- abstract + + +JSON Pointer is a syntax for specifying locations in a JSON document, +starting from the document root. This document defines an extension +to the JSON Pointer syntax, allowing relative locations from within +the document. + +--- middle + +# Introduction + +JSON Pointer ([RFC 6901](#RFC6901)) is a syntax for specifying +locations in a JSON document, starting from the document root. This +document defines a related syntax allowing identification of relative locations +from within the document. + + +# Conventions and Terminology + +{::boilerplate bcp14-tagged} + + +# Syntax + +A Relative JSON Pointer is a Unicode string in UTF-8 encoding (see RFC 8259, +[Section 8](#RFC8259)), comprising a non-negative integer, +an optional index adjustment consisting of '+' (%x2B) or '-' (%x2D) followed +by a positive integer, followed by either a '#' (%x23) character or +a JSON Pointer ([RFC 6901](#RFC6901)). + +The separation between the integer prefix (with optional adjustment) +and the JSON Pointer will +always be unambiguous, because a JSON Pointer must be either zero- +length or start with a '/' (%x2F). Similarly, a JSON Pointer will +never be ambiguous with the '#'. + +The ABNF syntax of a Relative JSON Pointer is: + +~~~~ abnf9110 + relative-json-pointer = origin-specification ( "#" / json-pointer ) + ; json-pointer from RFC 6901 + + origin-specification = non-negative-integer [ index-manipulation ] + index-manipulation = ( "+" / "-" ) positive-integer + non-negative-integer = "0" / positive-integer + positive-integer = %x31-39 *DIGIT + ; digits without a leading zero +~~~~ + + +# Evaluation + +Evaluation of a Relative JSON Pointer begins with a reference to a +value within a JSON document, and completes with either a value +within that document, a string corresponding to an object member, or +integer value representing an array index. + +Evaluation begins by processing the non-negative-integer prefix. +This can be found by taking the longest continuous sequence of decimal +digits available, starting from the beginning of the string, taking +the decimal numerical value. If the value is zero, the following steps +are skipped. If this value is more than zero, then the following steps +are repeated that number of times: + +> > If the current referenced value is the root of the document, then +> evaluation fails (see below). + +> > If the referenced value is an item within an array, then the new +> referenced value is that array. + +> > If the referenced value is an object member within an object, then +> the new referenced value is that object. + + + + +If the next character is a plus ("+") or minus ("-"), followed by another +continuous sequence of decimal digits, the following steps +are taken using the decimal numeric value of that plus or minus sign +and decimal sequence: + +> > If the current referenced value is not an item of an array, +> then evaluation fails (see below). + +> > If the referenced value is an item of an array, then the +> new referenced value is the item of the array indexed by +> adding the decimal value (which may be negative), to the +> index of the current referenced value. + + + + +If the remainder of the Relative JSON Pointer is a JSON Pointer, then +evaluation proceeds as per [RFC 6901, Section 5](#RFC6901) with the +modification that the initial reference +being used is the reference currently being held (which may not be +root of the document). + +Otherwise (when the remainder of the Relative JSON Pointer is the +character '#'), the final result is determined as follows: + +> > If the current referenced value is the root of the document, then +> evaluation fails (see below). + +> > If the referenced value is an item within an array, then the final +> evaluation result is the value's index position within the array. + +> > If the referenced value is an object member within an object, then +> the new referenced value is the corresponding member name. + + + + + +# JSON String Representation + +The concerns surrounding JSON String representation of a Relative +JSON Pointer are identical to those laid out in [RFC 6901, Section 5](#RFC6901). + +## Examples + +For example, given the JSON document: + +~~~~ + { + "foo": ["bar", "baz", "biz"], + "highly": { + "nested": { + "objects": true + } + } + } +~~~~ + +Starting from the value "baz" (inside "foo"), the following JSON +strings evaluate to the accompanying values: + +~~~~ + "0" "baz" + "1/0" "bar" + "0-1" "bar" + "2/highly/nested/objects" true + "0#" 1 + "0+1#" 2 + "1#" "foo" +~~~~ + +Starting from the value {"objects":true} (corresponding to the member +key "nested"), the following JSON strings evaluate to the +accompanying values: + +~~~~ + "0/objects" true + "1/nested/objects" true + "2/foo/0" "bar" + "0#" "nested" + "1#" "highly" +~~~~ + + + +# Non-use in URI Fragment Identifiers + +Unlike a JSON Pointer, a Relative JSON Pointer can not be used in a +URI fragment identifier. Such fragments specify exact positions +within a document, and therefore Relative JSON Pointers are not +suitable. + + +# Error Handling + +In the event of an error condition, evaluation of the JSON Pointer +fails to complete. + +Evaluation may fail due to invalid syntax, or referencing a non- +existent value. This specification does not define how errors are +handled. An application of JSON Relative Pointer SHOULD specify the +impact and handling of each type of error. + + +# Relationship to JSON Pointer + +Relative JSON Pointers are intended as a companion to JSON Pointers. +Applications MUST specify the use of each syntax separately. +Defining either JSON Pointer or Relative JSON Pointer as an acceptable +syntax does not imply that the other syntax is also acceptable. + + +# Acknowledgements + +The language and structure of this specification are based heavily on {{RFC6901}}, +sometimes quoting it outright. + +This draft remains primarily as written and published by Geraint Luff, +with only minor subsequent alterations under new editorship. + + +# Security Considerations + +Evaluation of a given Relative JSON Pointer is not guaranteed to +reference an actual JSON value. Applications using Relative JSON +Pointer should anticipate this situation by defining how a pointer +that does not resolve ought to be handled. + +As part of processing, a composite data structure may be assembled +from multiple JSON documents (in part or in full). In such cases, +applications SHOULD ensure that a Relative JSON Pointer does not +evaluate to a value outside the document for which is was written. + +Note that JSON pointers can contain the NUL (Unicode U+0000) +character. Care is needed not to misinterpret this character in +programming languages that use NUL to mark the end of a string. + + +--- back + +# ChangeLog + +[^CREF1] + +[^CREF1]: This section to be removed before leaving Internet-Draft status. + +draft-handrews-relative-json-pointer-03 +: * Fix ABNF omission for using # with index manipulation + + * Clarify handling of leading "0" + +draft-bhutton-relative-json-pointer-00 +: * Add array forward and backward index manipulation + +draft-handrews-relative-json-pointer-02 +: * Update to the latest JSON RFC + +draft-handrews-relative-json-pointer-01 +: * The initial number is "non-negative", not "positive" + +draft-handrews-relative-json-pointer-00 +: * Revived draft with identical wording and structure. + + * Clarified how to use alongside JSON Pointer. + +draft-luff-relative-json-pointer-00 +: * Initial draft. + + + diff --git a/relative-json-pointer.xml b/relative-json-pointer.xml deleted file mode 100644 index 0572a790..00000000 --- a/relative-json-pointer.xml +++ /dev/null @@ -1,363 +0,0 @@ - - - - -]> - - - - - - - - - - - Relative JSON Pointers - - -
- - - Cambridge - UK - - luffgd@gmail.com -
- - - -
- andrews_henry@yahoo.com -
- - - -
- ben@jsonschema.dev - https://jsonschema.dev -
- - - - Internet Engineering Task Force - JSON - JavaScript - Object - Notation - - - - - JSON Pointer is a syntax for specifying locations in a JSON document, - starting from the document root. This document defines an extension - to the JSON Pointer syntax, allowing relative locations from within - the document. - - - - - -
- - JSON Pointer (RFC 6901) is a syntax for specifying - locations in a JSON document, starting from the document root. This - document defines a related syntax allowing identification of relative locations - from within the document. - -
- -
- - - - The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", - "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be - interpreted as described in RFC 2119. - -
- -
- - A Relative JSON Pointer is a Unicode string in UTF-8 encoding (see RFC 8259, - Section 8), comprising a non-negative integer, - an optional index adjustment consisting of '+' (%x2B) or '-' (%x2D) followed - by a positive integer, followed by either a '#' (%x23) character or - a JSON Pointer (RFC 6901). - - - The separation between the integer prefix (with optional adjustment) - and the JSON Pointer will - always be unambiguous, because a JSON Pointer must be either zero- - length or start with a '/' (%x2F). Similarly, a JSON Pointer will - never be ambiguous with the '#'. - - - The ABNF syntax of a Relative JSON Pointer is: - - -
- -
- - Evaluation of a Relative JSON Pointer begins with a reference to a - value within a JSON document, and completes with either a value - within that document, a string corresponding to an object member, or - integer value representing an array index. - - - Evaluation begins by processing the non-negative-integer prefix. - This can be found by taking the longest continuous sequence of decimal - digits available, starting from the beginning of the string, taking - the decimal numerical value. If the value is zero, the following steps - are skipped. If this value is more than zero, then the following steps - are repeated that number of times: - - - If the current referenced value is the root of the document, then - evaluation fails (see below). - - - If the referenced value is an item within an array, then the new - referenced value is that array. - - - If the referenced value is an object member within an object, then - the new referenced value is that object. - - - - - If the next character is a plus ("+") or minus ("-"), followed by another - continuous sequence of decimal digits, the following steps - are taken using the decimal numeric value of that plus or minus sign - and decimal sequence: - - - If the current referenced value is not an item of an array, - then evaluation fails (see below). - - - If the referenced value is an item of an array, then the - new referenced value is the item of the array indexed by - adding the decimal value (which may be negative), to the - index of the current referenced value. - - - - - If the remainder of the Relative JSON Pointer is a JSON Pointer, then - evaluation proceeds as per - RFC 6901, Section 5 - with the modification that the initial reference - being used is the reference currently being held (which may not be - root of the document). - - - Otherwise (when the remainder of the Relative JSON Pointer is the - character '#'), the final result is determined as follows: - - - If the current referenced value is the root of the document, then - evaluation fails (see below). - - - If the referenced value is an item within an array, then the final - evaluation result is the value's index position within the array. - - - If the referenced value is an object member within an object, then - the new referenced value is the corresponding member name. - - - -
- -
- - The concerns surrounding JSON String representation of a Relative - JSON Pointer are identical to those laid out in - RFC 6901, Section 5. - -
-
- - For example, given the JSON document: - - - - -
-
- - Starting from the value "baz" (inside "foo"), the following JSON - strings evaluate to the accompanying values: - - - - -
-
- - Starting from the value {"objects":true} (corresponding to the member - key "nested"), the following JSON strings evaluate to the - accompanying values: - - - - -
-
-
- -
- - Unlike a JSON Pointer, a Relative JSON Pointer can not be used in a - URI fragment identifier. Such fragments specify exact positions - within a document, and therefore Relative JSON Pointers are not - suitable. - -
- -
- - In the event of an error condition, evaluation of the JSON Pointer - fails to complete. - - - Evaluation may fail due to invalid syntax, or referencing a non- - existent value. This specification does not define how errors are - handled. An application of JSON Relative Pointer SHOULD specify the - impact and handling of each type of error. - -
- -
- - Relative JSON Pointers are intended as a companion to JSON Pointers. - Applications MUST specify the use of each syntax separately. - Defining either JSON Pointer or Relative JSON Pointer as an acceptable - syntax does not imply that the other syntax is also acceptable. - -
- -
- - The language and structure of this specification are based heavily on - , sometimes quoting it outright. - - - This draft remains primarily as written and published by Geraint Luff, - with only minor subsequent alterations under new editorship. - -
- -
- - Evaluation of a given Relative JSON Pointer is not guaranteed to - reference an actual JSON value. Applications using Relative JSON - Pointer should anticipate this situation by defining how a pointer - that does not resolve ought to be handled. - - - As part of processing, a composite data structure may be assembled - from multiple JSON documents (in part or in full). In such cases, - applications SHOULD ensure that a Relative JSON Pointer does not - evaluate to a value outside the document for which is was written. - - - Note that JSON pointers can contain the NUL (Unicode U+0000) - character. Care is needed not to misinterpret this character in - programming languages that use NUL to mark the end of a string. - -
- - - - - - &RFC2119; - &RFC6901; - - - - &RFC8259; - - -
- - This section to be removed before leaving Internet-Draft status. - - - - - - Fix ABNF omission for using # with index manipulation - Clarify handling of leading "0" - - - - - Add array forward and backward index manipulation - - - - - Update to the latest JSON RFC - - - - - The initial number is "non-negative", not "positive" - - - - - Revived draft with identical wording and structure. - Clarified how to use alongside JSON Pointer. - - - - - Initial draft. - - - - -
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