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claude-code - 💡(How to fix) Fix VSCode extension v2.1.142: 'claude-vscode' IDE-bridge MCP fails tools/list with -32601 on every session, adds ~50s to cold start

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The IDE-bridge MCP server (claude-vscode) injected by the VS Code extension fails tools/list with MCP error -32601 (Method not found) on every session start. The CLI retries once, fails, and logs an error event. While the error doesn't crash the session, the failed handshake measurably delays initialization on slow hosts (observed ~52s between MCP startup and the final error in one cold session).

This server is presumably resources-only (IDE selection, diagnostics) and intentionally doesn't expose tools/list. If so, the client should either skip the call (when the server's initialize response indicates no tools capability) or treat -32601 as a silent zero-tools result rather than a logged error + retry.

Error Message

The IDE-bridge MCP server (claude-vscode) injected by the VS Code extension fails tools/list with MCP error -32601 (Method not found) on every session start. The CLI retries once, fails, and logs an error event. While the error doesn't crash the session, the failed handshake measurably delays initialization on slow hosts (observed ~52s between MCP startup and the final error in one cold session). This server is presumably resources-only (IDE selection, diagnostics) and intentionally doesn't expose tools/list. If so, the client should either skip the call (when the server's initialize response indicates no tools capability) or treat -32601 as a silent zero-tools result rather than a logged error + retry. {"debug":"tools/list failed (MCP error -32601: Method not found); retrying once","timestamp":"2026-05-16T01:11:27.665Z","sessionId":"d09595f5-...","cwd":"/workspaces/cloud-ingenium"} {"error":"Failed to fetch tools: MCP error -32601: Method not found","timestamp":"2026-05-16T01:11:27.666Z","sessionId":"d09595f5-...","cwd":"/workspaces/cloud-ingenium"} In the most recent cold session, the log file was created at 01:10:35 and the final tools/list error landed at 01:11:27 — a 52-second gap before the bridge gave up. That gap correlates with felt session-load slowness, particularly when stacked with #58438 (config-cache pre-launch). 3. Treat -32601 from a server with no declared tools capability as success-with-zero-tools rather than retrying + logging an error

Root Cause

The IDE-bridge MCP server (claude-vscode) injected by the VS Code extension fails tools/list with MCP error -32601 (Method not found) on every session start. The CLI retries once, fails, and logs an error event. While the error doesn't crash the session, the failed handshake measurably delays initialization on slow hosts (observed ~52s between MCP startup and the final error in one cold session).

This server is presumably resources-only (IDE selection, diagnostics) and intentionally doesn't expose tools/list. If so, the client should either skip the call (when the server's initialize response indicates no tools capability) or treat -32601 as a silent zero-tools result rather than a logged error + retry.

Code Example

{"debug":"tools/list failed (MCP error -32601: Method not found); retrying once","timestamp":"2026-05-16T01:11:27.665Z","sessionId":"d09595f5-...","cwd":"/workspaces/cloud-ingenium"}
{"error":"Failed to fetch tools: MCP error -32601: Method not found","timestamp":"2026-05-16T01:11:27.666Z","sessionId":"d09595f5-...","cwd":"/workspaces/cloud-ingenium"}
RAW_BUFFERClick to expand / collapse

Summary

The IDE-bridge MCP server (claude-vscode) injected by the VS Code extension fails tools/list with MCP error -32601 (Method not found) on every session start. The CLI retries once, fails, and logs an error event. While the error doesn't crash the session, the failed handshake measurably delays initialization on slow hosts (observed ~52s between MCP startup and the final error in one cold session).

This server is presumably resources-only (IDE selection, diagnostics) and intentionally doesn't expose tools/list. If so, the client should either skip the call (when the server's initialize response indicates no tools capability) or treat -32601 as a silent zero-tools result rather than a logged error + retry.

Environment

  • VS Code Insiders, extension Anthropic.claude-code v2.1.142, linux-arm64
  • Running inside a LinuxKit ARM64 devcontainer (GitHub Codespaces-style)
  • Native binary: /home/vscode/.vscode-server-insiders/extensions/anthropic.claude-code-2.1.142-linux-arm64/resources/native-binary/claude

Reproduction

  1. Open a Claude Code session in VS Code Insiders
  2. Inspect ~/.cache/claude-cli-nodejs/<cwd-slug>/mcp-logs-claude-vscode/<latest>.jsonl

Every single session log on this host (sampled 2026-05-14 through 2026-05-16, 5 consecutive sessions) shows exactly the same two-record sequence:

{"debug":"tools/list failed (MCP error -32601: Method not found); retrying once","timestamp":"2026-05-16T01:11:27.665Z","sessionId":"d09595f5-...","cwd":"/workspaces/cloud-ingenium"}
{"error":"Failed to fetch tools: MCP error -32601: Method not found","timestamp":"2026-05-16T01:11:27.666Z","sessionId":"d09595f5-...","cwd":"/workspaces/cloud-ingenium"}

100% reproducible — never seen a session log without it.

Timing concern

In the most recent cold session, the log file was created at 01:10:35 and the final tools/list error landed at 01:11:27 — a 52-second gap before the bridge gave up. That gap correlates with felt session-load slowness, particularly when stacked with #58438 (config-cache pre-launch).

Suggested fixes (any one of these resolves the noise)

  1. Implement tools/list on the IDE bridge returning an empty array [] (simplest, makes the call succeed)
  2. Suppress the request when initialize response has no tools capability (cleaner protocol use)
  3. Treat -32601 from a server with no declared tools capability as success-with-zero-tools rather than retrying + logging an error

Either #1 or #2 would also shorten cold-start latency on slow hosts.

Related

  • #58438 — Same host's other startup-slowness symptom (config-cache pre-launch 11-51s)

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#LLM response#prompt template#agent execution#callback error#memory management

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claude-code - 💡(How to fix) Fix VSCode extension v2.1.142: 'claude-vscode' IDE-bridge MCP fails tools/list with -32601 on every session, adds ~50s to cold start