feat: Implement SEP-986: Tool Name Guidance #1550
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Kludex
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Oct 31, 2025
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| @field_validator("name") | ||
| @classmethod | ||
| def _validate_tool_name(cls, value: str) -> str: | ||
| if not (1 <= len(value) <= 128): | ||
| raise ValueError(f"Invalid tool name length: {len(value)}. Tool name must be between 1 and 128 characters.") | ||
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| if not TOOL_NAME_PATTERN.fullmatch(value): | ||
| raise ValueError("Invalid tool name characters. Allowed: A-Z, a-z, 0-9, underscore (_), dash (-), dot (.).") | ||
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| return value | ||
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| """ | ||
| See [MCP specification](https://modelcontextprotocol.io/specification/draft/server/tools#tool-names) | ||
| for more information on tool naming conventions. | ||
| """ |
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@maxisbey This is a less verbose way to write the same thing:
from typing import Annotated
from pydantic import StringConstraints
tool: Annotated[str, StringConstraints(max_length=128, pattern=r"^[A-Za-z0-9_.-]+$")]I'm not sure if this should be applied on BaseMetadata, but if not, please drop the inheritance, and apply this here.
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Btw, most or all the field_validators in this code source can be replaced by proper annotated versions - that you can see are cuter.
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I personally don't think there's a need to test that Pydantic is working as expected.
maxisbey
added
improves spec compliance
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Implement SEP-986: Tool Name Guidance for Tool Type
Changes
re.compile(r"^[A-Za-z0-9_.-]+$")that raises an error for invalid characters:Motivation and Context
Related issues: SEP-986 #1537
Implements the guidance from modelcontextprotocol/modelcontextprotocol#986
How Has This Been Tested?
Unit Tests
Valid Values
getUserDATA_EXPORT_v2admin.tools.listaZ9_.-"x" * 128(max length)Invalid Values
""(empty string)"x" * 129(exceeds max length)has spacecomma,namenot/allowedname@name#name$Breaking Changes
Types of changes
Checklist
Additional context