how to manage multi streamable http server lifespan

[AniviaTn]

Describe the bug
I write a multi streamable http server example according to your readme doc, but only the mcp server which pass the session_manager.run() to FastAPI works right

To Reproduce
mcp python sdk ver 1.8.1

mcp server code

from fastapi import FastAPI
import uvicorn
from mcp.server.fastmcp import FastMCP


echo_mcp = FastMCP(name="EchoServer", stateless_http=True)


@echo_mcp.tool(description="A simple echo tool")
def echo(message: str) -> str:
 return f"Echo: {message}"

math_mcp = FastMCP(name="MathServer", stateless_http=True)


@math_mcp.tool(description="A simple add tool")
def add_two(m: int, n: int) -> int:
 return m + n


app = FastAPI(lifespan=lambda app: echo_mcp.session_manager.run())
app.mount("/echo", echo_mcp.streamable_http_app())
app.mount("/math", math_mcp.streamable_http_app())


if __name__ == "__main__":
 uvicorn.run(app, host="127.0.0.1", port=8000)

mcp client code

import asyncio
from mcp import ClientSession
from mcp.client.streamable_http import streamablehttp_client


async def main():
 server_url = "http://127.0.0.1:8000/math/mcp"

 async with streamablehttp_client(server_url) as (read, write, _):
 async with ClientSession(read, write) as session:
 await session.initialize()
 tools = await session.list_tools()
 tools = tools.tools

 print(f"found {len(tools)} tools:")

if __name__ == "__main__":
 asyncio.run(main())

Expected behavior
Every mcp server works right.

Error Stack

/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/bin/python /Users/karsalina/PycharmProjects/playGround/script/http_server.py 
INFO: Started server process [44368]
INFO: Waiting for application startup.
[05/14/25 16:21:02] INFO StreamableHTTP streamable_http_manager.py:109
 session manager 
 started 
INFO: Application startup complete.
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO: 127.0.0.1:49685 - "POST /math/mcp HTTP/1.1" 307 Temporary Redirect
INFO: 127.0.0.1:49687 - "POST /math/mcp/ HTTP/1.1" 500 Internal Server Error
ERROR: Exception in ASGI application
Traceback (most recent call last):
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/uvicorn/protocols/http/httptools_impl.py", line 411, in run_asgi
 result = await app( # type: ignore[func-returns-value]
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/uvicorn/middleware/proxy_headers.py", line 69, in __call__
 return await self.app(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/fastapi/applications.py", line 1054, in __call__
 await super().__call__(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/applications.py", line 112, in __call__
 await self.middleware_stack(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/errors.py", line 187, in __call__
 raise exc
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/errors.py", line 165, in __call__
 await self.app(scope, receive, _send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
 await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
 raise exc
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
 await app(scope, receive, sender)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 714, in __call__
 await self.middleware_stack(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 734, in app
 await route.handle(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 460, in handle
 await self.app(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/applications.py", line 112, in __call__
 await self.middleware_stack(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/errors.py", line 187, in __call__
 raise exc
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/errors.py", line 165, in __call__
 await self.app(scope, receive, _send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
 await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
 raise exc
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
 await app(scope, receive, sender)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 714, in __call__
 await self.middleware_stack(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 734, in app
 await route.handle(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 460, in handle
 await self.app(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/mcp/server/fastmcp/server.py", line 782, in handle_streamable_http
 await self.session_manager.handle_request(scope, receive, send)
 File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/mcp/server/streamable_http_manager.py", line 137, in handle_request
 raise RuntimeError("Task group is not initialized. Make sure to use run().")
RuntimeError: Task group is not initialized. Make sure to use run().

[Shaw-shaw]

I have the same problem

[ihrpr]

thank you for reporting this! Updated the example in readme

[AydarAkhmetzyanov]

its failing for me too for basic example with mcp streamable HTTP transport, what is the solution?

[kanweiwei]

thank you for reporting this! Updated the example in readme

Based on your example, if I want to access the database in an mcp server and I want to use lifespan, but I don't know exactly how to write it

[bygzyz]

got the same problem!

by the way, anybody knows how to merge FastAPI's lifespan and FastMCP's lifespan?

blow is my test code:

`python
from fastmcp import FastMCP
from starlette.routing import Mount

from contextlib import asynccontextmanager

mcp = FastMCP(name="MyServer")
mcp_app = mcp.http_app(path='/mcp')

from fastapi import FastAPI

@asynccontextmanager
async def main_app_lifespan(app: FastAPI):
# do some main app's init work
pass

app = FastAPI(lifespan=mcp_app.lifespan, routes=[Mount('/mcp_http_kn', app=mcp_app)])

@app.get("/test")
async def test():
return 'test'

@mcp.tool()
def greet(name: str) -> str:
"""Greet a user by name."""
return f"Hello, {name}!"

if name == "main":
import uvicorn
uvicorn.run(app, host="0.0.0.0", port=8000)

`

[Nayjest]

I reported the same issue in a different usage context: #838

In my opinion, this appears to be an issue with the Python SDK, not a documentation issue.

The FastMCP class should be able to handle its intended functionality without additional setup, or it should fail early with a clear error message if additional configuration is needed.

[ihrpr]

its failing for me too for basic example with mcp streamable HTTP transport, what is the solution?

Please can you share the example and how you are running it?

[thanusiak]

@bygzyz
Please see: https://www.reddit.com/r/mcp/comments/1kizgw2/fastapi_fastmcp_integration_question/