Add configurable JSON Schema target specification for OpenAI

[ashburnham]

Summary

This PR adds support for configurable JSON Schema target specification to improve compatibility with OpenAI endpoints and other systems that require specific JSON Schema versions.

Changes Made

• Added jsonSchemaSpec option to ServerOptions interface
• Added _jsonSchemaSpec property to Server class with default value of 'jsonSchema7'
• Updated McpServer to use the configured target in zodToJsonSchema calls
• Imported Target type from zod-to-json-schema for type safety

Benefits

• OpenAI Compatibility: Allows servers to generate JSON schemas compatible with OpenAI endpoints
• Flexibility: Developers can choose the appropriate JSON Schema specification for their use case
• Backward Compatibility: Defaults to 'jsonSchema7' to maintain existing behavior

Usage Example

const server = new McpServer({
  name: "my-server",
  version: "1.0.0"
}, {
  jsonSchemaSpec: 'openApi3' // For OpenAI compatibility
});

Files Changed

• src/server/index.ts: Added jsonSchemaSpec option and property
• src/server/mcp.ts: Updated to use configured target in schema generation

Motivation and Context

• Many people will be using MCP with OpenAI endpoints. OpenAI only works with a specific subset of JSON Schema. It would be useful to be able to retain other schema functionality when creating servers that are sometimes consumed by OpenAI, sometimes by other providers.

How Has This Been Tested?

I made a non-OpenAI compliant schema and used them consumed it with the OpenAI responses API

Breaking Changes

Nope

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Nope - does what it says on the tin

[paoloricciuti]

Do you have any pointers to some docs where it shows the incompatibility of OpenAi with jsonSchema7?

[ashburnham]

Only my own experience 2 weeks ago, specifically using it to creat custom mcps for use in deep research
https://platform.openai.com/docs/guides/deep-research

the error says schema doesn't match expected schema (which is v limited to fetch/search). It's that specifci schema does does not work with jsonSchema7

[ashburnham]

merge conflicts resolved @rafaelportomoura