dict[str, T] tool return types lose Annotated/Field metadata in output schema

[zlucas03]

Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

Tools that return a string-keyed dict (dict[str, T]) lose any Annotated/Field metadata on the return type when the output schema is generated. A Field(description=...) on the return annotation shows up in the output schema for every other return type, but for dict[str, T] it's dropped.

I'd expect the description to be preserved, the same as other return types. Looks like the dict[str, T] branch in _try_create_model_and_schema builds the model from the Annotated-stripped type instead of the original annotation (there's an existing TODO on that line).

Have a simple, tested fix ready to go. Love the project and would love to contribute if possible!

Example Code

from typing import Annotated
from pydantic import Field
from mcp.server.mcpserver.utilities.func_metadata import func_metadata

def get_config() -> Annotated[dict[str, int], Field(description="Configuration values")]:
    return {"timeout": 30}

print(func_metadata(get_config).output_schema)
# {'type': 'object', 'additionalProperties': {'type': 'integer'}, 'title': 'get_configDictOutput'}
# expected to also include: 'description': 'Configuration values'

Python & MCP Python SDK

Python 3.14.5
mcp: main branch (mcpserver / V2)

[zlucas03]

Thanks for jumping on this, @anneheartrecord — this is the same approach I'd landed on (routing original_annotation through to _create_dict_model instead of the stripped type_expr), so +1 on the direction. One thing I confirmed while testing locally: un-annotated dict[str, str] and dict[str, Any] output schemas come out byte-for-byte identical, so it's safe as a non-breaking change.

[anneheartrecord]

Thanks @zlucas03, good to have that confirmed independently. The byte-for-byte match on un-annotated dict[str, str] and dict[str, Any] is exactly why I threaded original_annotation through instead of touching the stripped type_expr — existing schemas stay identical, only the annotated case changes. Fix is up in #2939.