How do I debug MCP issues?

[cseickel]

This is a great idea! I tried it out but it does not work. This is what I have in the mcp log file:

[
  {
    "debug": "Starting connection with timeout of 30000ms",
    "timestamp": "2025-09-05T14:25:25.616Z",
    "sessionId": "ce192d16-cd8b-4d92-b0b4-e13e3205d1c6",
    "cwd": "/home/user/claude-instructions"
  },
  {
    "error": "Server stderr: Resolving dependencies",
    "timestamp": "2025-09-05T14:25:25.634Z",
    "sessionId": "ce192d16-cd8b-4d92-b0b4-e13e3205d1c6",
    "cwd": "/home/user/claude-instructions"
  },
  {
    "error": "Server stderr: Resolved, downloaded and extracted [4]",
    "timestamp": "2025-09-05T14:25:27.294Z",
    "sessionId": "ce192d16-cd8b-4d92-b0b4-e13e3205d1c6",
    "cwd": "/home/user/claude-instructions"
  },
  {
    "error": "Server stderr: Saved lockfile",
    "timestamp": "2025-09-05T14:25:27.324Z",
    "sessionId": "ce192d16-cd8b-4d92-b0b4-e13e3205d1c6",
    "cwd": "/home/user/claude-instructions"
  },
  {
    "debug": "Connection failed after 1719ms: MCP error -32000: Connection closed",
    "timestamp": "2025-09-05T14:25:27.334Z",
    "sessionId": "ce192d16-cd8b-4d92-b0b4-e13e3205d1c6",
    "cwd": "/home/user/claude-instructions"
  },
  {
    "error": "Connection failed: MCP error -32000: Connection closed",
    "timestamp": "2025-09-05T14:25:27.334Z",
    "sessionId": "ce192d16-cd8b-4d92-b0b4-e13e3205d1c6",
    "cwd": "/home/user/claude-instructions"
  },
  {
    "debug": "Starting connection with timeout of 30000ms",
    "timestamp": "2025-09-05T14:26:16.127Z",
    "sessionId": "ce192d16-cd8b-4d92-b0b4-e13e3205d1c6",
    "cwd": "/home/user/claude-instructions"
  },
  {
    "debug": "Connection failed after 8ms: MCP error -32000: Connection closed",
    "timestamp": "2025-09-05T14:26:16.135Z",
    "sessionId": "ce192d16-cd8b-4d92-b0b4-e13e3205d1c6",
    "cwd": "/home/user/claude-instructions"
  },
  {
    "error": "Connection failed: MCP error -32000: Connection closed",
    "timestamp": "2025-09-05T14:26:16.135Z",
    "sessionId": "ce192d16-cd8b-4d92-b0b4-e13e3205d1c6",
    "cwd": "/home/user/claude-instructions"
  }
]

The SessionStart hook throws this in the UI:

SessionStart:startup [npx -y cli-lsp-client start] failed with non-blocking status code 1: No stderr output

How can I debug? Are there any other log files?

[eli0shin]

You can use the logs command bunx cli-lsp-client logs to get the log file path for the current directory daemon.
What do you see for commands like:
bunx cli-lsp-client status
bunx cli-lsp-client start
If daemons are in a bad state, you can force them to stop with stop or stop-all.

Let me know what you find and I'll see if I can help resolve it.

[cseickel]

Thanks for responding and sorry for the delay. It turns out the problem is with the binary downloaded via npx/bunx. It always exits with error code 1 with no message of any kind, no matter what command I use. Even help / --help / -h outputs nothing to the console.

I checked out the repo and built and I am using that directly instead and it works!

This is obviously a different issue, but when testing it out I did notice that diagnostics are often stale which can be a problem. I am going to take a look at the code and see if I can do anything about that. Missing a new error is not so horrible because it will be revealed eventually, but returning an error that does not exist could cause bigger issues.

EDIT: I should mention I was testing with typescript on a mid-size full stack project.