fix(fetch): cap mcp dependency below 2.0 - #4611
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mcp>=1.1.3 had no upper bound, so a fresh `uvx mcp-server-fetch` resolved mcp 2.0.0. That release renamed McpError to MCPError and removed the low-level Server decorators, so server.py raised ImportError at line 6 and exited before writing an initialize response. Clients reported "connection closed: initialize response". Cap the requirement at mcp>=1.1.3,<2 and refresh uv.lock to match. The lock already pinned mcp 1.28.1, so CI was unaffected; only fresh resolves broke. Not a port to mcp 2.0: list_tools, list_prompts, call_tool, and get_prompt are all gone from the low-level Server and server.py uses all four. Verified with a real stdio handshake on Python 3.12. The published 2026.7.10 returns no initialize response; a wheel built from this change resolves mcp 1.29.0 and answers tools/list with ['fetch']. tests/test_dependencies.py covers the specifier.
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Fixes #4600
mcp>=1.1.3has no upper bound, so a freshuvx mcp-server-fetchnow resolves mcp 2.0.0, which renamedMcpErrortoMCPErrorand dropped the low-levelServerdecorators.server.pydies on the import at line 6 before writing anything to stdout, which the client sees asconnection closed: initialize response.This caps the requirement at
mcp>=1.1.3,<2and updatesuv.lockto match. The lock already pinned mcp 1.28.1, so CI never saw this; only fresh resolves are affected.I did not port fetch to mcp 2.0. It is not just the exception rename:
list_tools,list_prompts,call_tool, andget_promptare all gone from the low-levelServer, andserver.pyuses all four. That is a migration, not a bug fix.Verified on Linux, Python 3.12, uv 0.12.0, with a real JSON-RPC stdio handshake:
mcp-server-fetch==2026.7.10: no initialize response,ImportError: cannot import name 'McpError'mcp==1.29.0,initialize ok: server=mcp-fetch version=1.29.0,tools=['fetch']Added
tests/test_dependencies.py, which fails on the old specifier and passes on the new one.ruff checkandpyrightare clean.tests/test_server.py::test_empty_content_returns_errorfails on my machine both with and without this patch, because there is no Node.js on PATH and readabilipy falls back to pure-Python mode. Unrelated to this change.Not verified: I reproduced with my own stdio client, not with Codex, and the "after" run used a locally built wheel rather than a published one.
Two things for you to decide. First,
src/gitandsrc/timehave the same unbounded range and break the same way under mcp 2.0.0 (mcp-server-timeon the sameMcpErrorimport,mcp-server-giton'Server' object has no attribute 'list_tools'). I left them out to keep this scoped to the reported issue, happy to add the same one-line cap to both. Second, if you would rather port to mcp 2.0 than cap, close this.Thanks to @tking007 for the report, including the correct diagnosis and the
--with "mcp<2"workaround.