Initial Checks
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
Initial Checks
Description
If you try to use a tool a which is wrapped and uses
from __future__ import annotationssetup fails with andInvalidSignatureexception e.g.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
Python & MCP Python SDK