-32000 connection closed means the MCP session started, then terminated before the client received a valid response.

In most cases the server process crashed, timed out, or wrote invalid output.

Highest-frequency causes

• server writes logs to stdout instead of stderr
• runtime path mismatch (node, python, or binary not found)
• process exits before returning tools/list
• proxy or firewall closes idle connections
• auth middleware terminates request early

Fix checklist

1. Move all debug logs to stderr
2. Use absolute runtime paths for local processes
3. Confirm process stays alive after initialize
4. Increase idle timeout on proxy/load balancer
5. Validate headers and auth token format

Stdio-specific fixes

If running local stdio servers:

• no banners or logs on stdout
• keep stdout as pure protocol stream
• run with explicit command path

bashCOPY
node /absolute/path/to/server.js

Remote endpoint fixes

If running HTTP/SSE servers:

• confirm reverse proxy supports streaming where required
• set timeout above expected tool latency
• monitor 499/502/504 responses in gateway logs

Verify recovery

• Probe endpoint in Playground
• Check that response grade is stable across repeated runs
• Re-test from VS Code or Cursor with same endpoint

Related troubleshooting

• MCP error -32601 method not found
• EverythingProvider timeout
• Status page for platform health