AttributeError: module 'mcp.server' has no attribute 'stdio_server' while running mcp-proxy against an SSE server

4 answers

• Best answerAgentArmor teamTeam3d ago

  Fixed in mcp-proxy 0.3.1.

  The maintainer tentatively attributed the crash to module changes in the newer mcp library: "I may have identified the root cause. The new version of mcp introduces modules changes, which could result in a similar issue." He asked the reporter to update mcp-proxy to 0.3.1, and the reporter confirmed the fix with "Works! Many thanks."

  To apply the fix, upgrade mcp-proxy to 0.3.1 (the maintainer's instruction was "update to mcp-proxy==0.3.1"). The reporter's installation lived under uv's tool directory on Python 3.13 (/Users/duncan/.local/share/uv/tools/mcp-proxy/), so if you installed the same way, update that uv tool.

  The reporter's own SSE server (mcp-clj, written in Clojure without an official SDK) had already responded correctly to the initialize request; the failure happened in the proxy's forwarding layer (mcp_proxy/sse_client.py, via mcp/client/sse.py), where the traceback shows a CancelledError. The thread does not describe any configuration or SSE-server changes, and the maintainer did not blame the reporter's protocol implementation.

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• AgentArmor teamTeam3d ago

  What a GitHub user tried on GitHub (Didn't work)

  Reporter ran mcp-proxy (installed via uv on Python 3.13) against a custom Clojure SSE server, using Claude Desktop on macOS. During the initialize exchange the proxy crashed with the thread-title AttributeError and a CancelledError traceback in mcp/client/sse.py and mcp_proxy/sse_client.py.

  Source: https://github.com/sparfenyuk/mcp-proxy/issues/15 (opens external site) ↗

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• AgentArmor teamTeam3d ago

  What @sparfenyuk tried on GitHub (Worked)

  Maintainer asked the reporter to update mcp-proxy to 0.3.1, citing module changes in the newer mcp version as the possible cause. Reporter confirmed the update fixed the problem.

  Source: https://github.com/sparfenyuk/mcp-proxy/issues/15#issuecomment-2578339111 (opens external site) ↗

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• AgentArmor teamTeam3d ago

  What @sparfenyuk tried on GitHub (Outcome unclear)

  Maintainer initially suspected the mcp library itself and planned to upgrade it to v1.2.0, but this was never verified as a fix before the mcp-proxy 0.3.1 update.

  Source: https://github.com/sparfenyuk/mcp-proxy/issues/15#issuecomment-2578287558 (opens external site) ↗

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