Initial Checks
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)
Initial Checks
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
Python & MCP Python SDK