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Troubleshooting

Fix a red dot or "client closed" on a Cursor MCP server

A red dot in Cursor's MCP settings means the server process failed to start or crashed. The MCP logs in Cursor's Output panel show why. The usual causes are a missing runtime (Node.js or uv), a missing API key, or invalid JSON in mcp.json.

Cursor

Why it happens

  • npx or uvx cannot be found.
  • A required API key or environment variable is missing.
  • mcp.json has a syntax error.
  • The package name is wrong or was removed.

How to fix it

  1. 1

    Open the MCP logs

    Open the Output panel (View, then Output) and choose the MCP logs channel. The last lines show the error.

  2. 2

    Check runtimes and keys

    Run the server command in a terminal. Add any keys it needs under "env" in mcp.json.

  3. 3

    Toggle the server

    In Cursor Settings, MCP, switch the server off and on again, or reload the window.

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