fastapi-mcp does not register tool even with correct operation_id

[wuhaiyi]

Hi all,

I’m currently trying to register a simple tool using fastapi-mcp with FastAPI. My endpoint looks like this:

from fastapi import FastAPI
from pydantic import BaseModel
from fastapi_mcp import FastApiMCP

app = FastAPI()

class DummyInput(BaseModel):
dummy: str = "hi"

@app.post("/test", operation_id="test_endpoint")
async def test_endpoint(input: DummyInput):
return {"message": f"Success: {input.dummy}"}

mcp = FastApiMCP(app, name="Test MCP", base_url="http://localhost:8000")
mcp.mount()

Then: curl -N -H "Accept: text/event-stream" http://localhost:8000/mcp
I only get:
event: endpoint
data: /mcp/messages/?session_id=...
But I expected to see /test registered as a tool.

I’ve verified:
• The endpoint uses POST and has a valid operation_id
• The input model is a BaseModel with valid fields
• mcp.mount() is called after all routes are registered
• mcp.to_openai_tool_spec() returns an empty list ([])

❓ Question
Is there anything I might be missing to get the tool properly registered and showing up in /mcp?
Thanks in advance!

[shira-ayal]

Hi @wuhaiyi ,
I'm not sure you are running the most updated version, as we changed and no longer have base_url in initializing the MCP.
Can you try again, and if it still don't work open a bug in issues (instead of a discussion)?
thanks!