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feat: add tool metadata in FastMCP.tool decorator #1463

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Merged
merged 5 commits into from
Oct 17, 2025
Merged

feat: add tool metadata in FastMCP.tool decorator #1463

merged 5 commits into from
Oct 17, 2025
+213 −8

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@mat-octave
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Adds a feature to add metadata to a tool using the FastMCP.tool decorator, passing it to the Tool object.

Motivation and Context

ChatGPT's App SDK expects information about UI resources to be in a tool's _meta field. The decorator FastMCP.tool didn't accept metadata but the field exists on the lower-level mcp.Tool object.

How Has This Been Tested?

I added metadata to mcp.tool(...) and started the server successfully. I used the Model Inspector to list the tools, and the metadata was visible in the schema.

Breaking Changes

No, this just adds an optional field meta.

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

@felixweinberger felixweinberger added this to the META Improvements milestone Oct 10, 2025
@felixweinberger felixweinberger added the needs maintainer action Potentially serious issue - needs proactive fix and maintainer attention label Oct 10, 2025
@gabteixeira gabteixeira mentioned this pull request Oct 10, 2025
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@felixweinberger felixweinberger linked an issue Oct 10, 2025 that may be closed by this pull request
Availability of the meta parameter in tool definition on the server #1462
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@BrandonShar BrandonShar mentioned this pull request Oct 10, 2025
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3 tasks
@maxisbey maxisbey mentioned this pull request Oct 13, 2025
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@BrandonShar BrandonShar mentioned this pull request Oct 14, 2025
Open
9 tasks
mat-octave and others added 3 commits October 14, 2025 11:47
@mat-octave
add output_schema override to support ChatGPT App SDK
88bc72d
@mat-octave
Revert "add output_schema override to support ChatGPT App SDK"
2c2cd0e 
This reverts commit 88bc72d.
@maxisbey
test: add comprehensive unit tests for tool metadata feature
cda1cf4 
Add tests covering:
- Adding metadata via ToolManager.add_tool()
- Adding metadata via FastMCP.tool() decorator
- Metadata preservation in Tool objects
- Metadata inclusion in MCPTool when listing tools
- Edge cases (None, empty dict, complex nested structures)
- Integration with tool annotations

All tests verify that the meta parameter correctly flows through
the tool registration and listing pipeline.
maxisbey
maxisbey approved these changes Oct 17, 2025
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Thanks for the submission @mat-octave ! I've gone ahead and pushed a unit test to your branch as well so we can get this merged :)

@maxisbey maxisbey enabled auto-merge (squash) October 17, 2025 11:15
@maxisbey maxisbey merged commit 98f8248 into modelcontextprotocol:main Oct 17, 2025
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@saqadri
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saqadri commented Oct 21, 2025

@maxisbey can we get a minor bump for the package published to pypi with these changes? Thank you! And thanks @mat-octave for fixing this!

@felixweinberger
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@maxisbey can we get a minor bump for the package published to pypi with these changes? Thank you! And thanks @mat-octave for fixing this!

We generally do releases on Thursdays, so this will be in there on 10/23

@saqadri
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saqadri commented Oct 21, 2025

@maxisbey can we get a minor bump for the package published to pypi with these changes? Thank you! And thanks @mat-octave for fixing this!

We generally do releases on Thursdays, so this will be in there on 10/23

Perfect, thank you @felixweinberger!

@juanlarrambebere
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Hi! Very eager to try this release as well!

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@maxisbey maxisbey maxisbey approved these changes

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META Improvements

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Availability of the meta parameter in tool definition on the server

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@mat-octave @saqadri @felixweinberger @juanlarrambebere @maxisbey