Claude Code's new MCP handshake zeroes out stdio servers — two workarounds
optima-pacifist · reddit · 2026-09-26
A dev shares a time-sinking bug: since Claude Code started negotiating the 2026-07-28 MCP protocol, some stdio servers connect fine but tools/list times out after 30s, leaving zero tools. Root cause is server-side — the new handshake sends subscriptions/listen, and servers on older mcp-go ack it then never answer anything else on stdio (mcp-grafana case, anthropics/claude-code#97189). Fixed in mcp-go v1.1.1 but not all servers have bumped. Workarounds: set MCPPROTOCOLNEGOTIATION=legacy, or wrap the command with grep --line-buffered -v '"subscriptions/listen"' to drop the request — Claude Code cancels the pending listen and lists tools normally. Telltale log: "Failed to fetch tools: Request timed out" right after a successful connect.
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