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

If you try to use a tool a which is wrapped and uses from __future__ import annotations setup fails with and InvalidSignature exception e.g.

mcp.server.fastmcp.exceptions.InvalidSignature: Unable to evaluate type annotation ForwardRef("Literal['literal'] | None")

The cause of this is that the global name space used for the lookup is the wrapper namespace and not the original function namespace.

Example Code

from __future__ import annotations

import logfire
from mcp.server.fastmcp import FastMCP

@logfire.instrument
def test_tool(location_type: Literal["literal"] | None = None) -> str:
    """Test tool."""
    return f"a is {location_type}"

mcp = FastMCP(
    "Wrap test",
    tools=[
        Tool.from_function(test_tool),
    ],
)

Python & MCP Python SDK

SDL: 1.14.1
Python: 3.13.7