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.
More from coding & agent
- Building a Semantic and Knowledge Layer on BigQuery and Exposing It to Agents — batmanparam · 2026-09-27
- OpenAI selects 35 builders for first Codex Physical Builds hardware cohort — OpenAIDevs · 2026-09-27
- Multi-Agent Bot Pipelines Keep Stalling: Direct-to-Harness Still Beats Bot Teams — Old_Grapefruit8774 · 2026-09-27
- Claude Opus 5.5 Chains Blender, Image-Gen and three.js Into Browser-Running 3D — burny_tech · 2026-09-27
- Claude kills plan mode the same day Google announces launching it — dotey · 2026-09-27
- Gary Marcus amplifies warning: large teams using AI agents likely have unknown security incidents — GaryMarcus · 2026-09-27