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Claude Code Issues / #20713

[BUG] MCP server connection fails with error -32000: Connection closed (race condition)

Resolved 💬 4 comments Opened Jan 25, 2026 by cav3n Closed Apr 1, 2026

Preflight Checklist

  • [x] I have searched existing issues and this hasn't been reported yet
  • [x] This is a single bug report (please file separate reports for different bugs)
  • [x] I am using the latest version of Claude Code

What's Wrong?

MCP servers fail to connect with MCP error -32000: Connection closed. The server starts correctly and responds to MCP protocol when tested manually, but Claude Code's connection drops before completing the handshake.

This is a re-filing of previously auto-closed issues that were never actually fixed:

  • #3071 (auto-closed due to inactivity)
  • #3184 (auto-closed, was assigned to @ashwin-ant)
  • #3634 (auto-closed due to inactivity)
  • #12449 (closed as duplicate of #3071)

Evidence This Is a Race Condition (Not Server Issue)

  1. SSH tunnel verified working - lsof -i :5522 confirms tunnel is active
  2. Direct mysql2 connection works:

``javascript
const conn = await mysql.createConnection({host: '127.0.0.1', port: 5522, ...});
// Result: Connected successfully! Query result: [ { test: 1 } ]
``

  1. MCP server starts correctly when tested manually:

``
[mcp-mysql] Starting with config: { host: '127.0.0.1', port: 5522, ... }
[mcp-mysql] Server connected and ready
``

  1. MCP protocol handshake works when tested directly:

``bash
echo '{"jsonrpc":"2.0","id":1,"method":"initialize",...}' | node index.js
# Returns valid response with tools
``

  1. Multiple packages all fail identically:
  • @benborla29/mcp-server-mysql@2.0.7 ❌
  • @benborla29/mcp-server-mysql@1.0.21 ❌
  • @sajithrw/mcp-mysql@1.0.0 ❌
  • @liangshanli/mcp-server-mysql@3.0.0 ❌
  • Custom local server with no stdout pollution ❌

Debug Log Evidence

2026-01-25T00:28:17.650Z [DEBUG] MCP server "mysql": Starting connection with timeout of 30000ms
2026-01-25T00:28:24.193Z [DEBUG] MCP server "mysql": Connection failed after 6544ms: MCP error -32000: Connection closed

The server process starts but Claude Code closes the connection before the MCP handshake completes.

What Should Happen?

MCP server should connect successfully when the server is running and responding correctly to the MCP protocol.

Error Messages/Logs

MCP error -32000: Connection closed

Steps to Reproduce

  1. Configure any MCP server in .mcp.json
  2. Ensure the server works when tested manually (stdin/stdout JSON-RPC)
  3. Run /mcp in Claude Code
  4. Observe: "Failed to reconnect to mysql" with error -32000 in debug logs

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.19

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Environment:

  • Node.js: v25.2.1
  • macOS Darwin 25.3.0

Workarounds attempted (all failed):

  • Clearing npx cache
  • Using different MCP server packages
  • Creating custom local MCP server with no stdout pollution
  • Adding explicit PATH and cwd to mcp.json
  • Renaming mcp.json to .mcp.json

Related external resources:

View original on GitHub ↗

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