mcp server always get initialization error

[guolisen]

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• Protocol Specification
• SDK Usage
• Server Implementation
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Your Question

I created a mcp server by FastMCP, I can ensure that the mcp server has already finished the initialization, due to the server has already process several tool request, but I also get following error:

    INFO:     192.168.182.1:2520 - "GET /sse HTTP/1.1" 200 OK
INFO:     192.168.182.1:2691 - "POST /messages/?session_id=aa9fa14634144092aed00e8a04f84ca4 HTTP/1.1" 202 Accepted
INFO:     192.168.182.1:2760 - "POST /messages/?session_id=aa9fa14634144092aed00e8a04f84ca4 HTTP/1.1" 202 Accepted
ERROR:    Exception in ASGI application
  + Exception Group Traceback (most recent call last):
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/uvicorn/protocols/http/h11_impl.py", line 403, in run_asgi
  |     result = await app(  # type: ignore[func-returns-value]
  |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |         self.scope, self.receive, self.send
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |     )
  |     ^
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/uvicorn/middleware/proxy_headers.py", line 60, in __call__
  |     return await self.app(scope, receive, send)
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/applications.py", line 112, in __call__
  |     await self.middleware_stack(scope, receive, send)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/middleware/errors.py", line 187, in __call__
  |     raise exc
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/middleware/errors.py", line 165, in __call__
  |     await self.app(scope, receive, _send)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
  |     await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
  |     raise exc
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
  |     await app(scope, receive, sender)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/routing.py", line 714, in __call__
  |     await self.middleware_stack(scope, receive, send)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/routing.py", line 734, in app
  |     await route.handle(scope, receive, send)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/routing.py", line 288, in handle
  |     await self.app(scope, receive, send)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/routing.py", line 76, in app
  |     await wrap_app_handling_exceptions(app, request)(scope, receive, send)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
  |     raise exc
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
  |     await app(scope, receive, sender)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/starlette/routing.py", line 73, in app
  |     response = await f(request)
  |                ^^^^^^^^^^^^^^^^
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/mcp/server/fastmcp/server.py", line 485, in handle_sse
  |     async with sse.connect_sse(
  |                ~~~~~~~~~~~~~~~^
  |         request.scope,
  |         ^^^^^^^^^^^^^^
  |         request.receive,
  |         ^^^^^^^^^^^^^^^^
  |         request._send,  # type: ignore[reportPrivateUsage]
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |     ) as streams:
  |     ^
  |   File "/home/lewis/.local/share/uv/python/cpython-3.13.2-linux-x86_64-gnu/lib/python3.13/contextlib.py", line 235, in __aexit__
  |     await self.gen.athrow(value)
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/mcp/server/sse.py", line 123, in connect_sse
  |     async with anyio.create_task_group() as tg:
  |                ~~~~~~~~~~~~~~~~~~~~~~~^^
  |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
  |     raise BaseExceptionGroup(
  |         "unhandled errors in a TaskGroup", self._exceptions
  |     ) from None
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/mcp/server/sse.py", line 131, in connect_sse
    |     yield (read_stream, write_stream)
    |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/mcp/server/fastmcp/server.py", line 490, in handle_sse
    |     await self._mcp_server.run(
    |     ...<3 lines>...
    |     )
    |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/mcp/server/lowlevel/server.py", line 483, in run
    |     async with AsyncExitStack() as stack:
    |                ~~~~~~~~~~~~~~^^
    |   File "/home/lewis/.local/share/uv/python/cpython-3.13.2-linux-x86_64-gnu/lib/python3.13/contextlib.py", line 768, in __aexit__
    |     raise exc
    |   File "/home/lewis/.local/share/uv/python/cpython-3.13.2-linux-x86_64-gnu/lib/python3.13/contextlib.py", line 751, in __aexit__
    |     cb_suppress = await cb(*exc_details)
    |                   ^^^^^^^^^^^^^^^^^^^^^^
    |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/mcp/shared/session.py", line 210, in __aexit__
    |     return await self._task_group.__aexit__(exc_type, exc_val, exc_tb)
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
    |     raise BaseExceptionGroup(
    |         "unhandled errors in a TaskGroup", self._exceptions
    |     ) from None
    | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
    +-+---------------- 1 ----------------
      | Traceback (most recent call last):
      |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/mcp/shared/session.py", line 324, in _receive_loop
      |     await self._received_request(responder)
      |   File "/home/lewis/mcp/mcp_k8s_server/.venv/lib/python3.13/site-packages/mcp/server/session.py", line 163, in _received_request
      |     raise RuntimeError(
      |         "Received request before initialization was complete"
      |     )
      | RuntimeError: Received request before initialization was complete
      +------------------------------------

I also add a parameter when create object of FastMCP

    # Create the MCP server with initialization timeout
# This helps prevent "Received request before initialization was complete" errors
# by automatically closing connections that don't initialize properly
mcp = FastMCP(
    config.server.name,
    host=config.server.host,
    port=config.server.port,
    settings={"initialization_timeout": 10.0}  # 10 second timeout
)

mcp server run code:

 mcp.run(transport="sse")

BTW: my mcp client is CherryStdio. I write a mcp client to connect server also has this kind of probelm. however when i deploy my mcp server to k8s POD, the error did not arise.

CherryStdio is a Typescript client, and my server is implement by python, whether this two kinds of mcp library has some issues?
https://github.com/CherryHQ/cherry-studio

requires-python = ">=3.13"
dependencies = [
"mcp>=1.6.0",
"pyyaml>=6.0.1",
"httpx>=0.28.1",
"click>=8.1.8",
"pydantic>=2.11.1",
"pydantic-settings>=2.8.1",
"pip>=25.0.1",
"debugpy>=1.8.13",
]

[G0rav]

Same, mine is working fine with cursor but I created my own client, not working with it.

[notabene00]

Same Received request before initialization was complete
Works well with Cursor, not working at all with Sage

[CaoChensy]

same

[olaservo]

Seems like this is an issue with FastMCP, could you create an issue there instead? If I'm just reading this wrong feel free to reopen, but either way I think you'll have a better chance getting help in the related repo you're relying on here.