Debugging

MCP Inspector

You can interactively test the MCP server using the official inspector:

npx @modelcontextprotocol/inspector

Then open the URL it prints (e.g., http://localhost:5173) and connect:

• Transport: STDIO
• Command: prometheus-mcp
• Args (optional): --mcp --prometheus-url http://localhost:9090

Click Connect, then use the Tools tab to list and call the Prometheus tools.

TIP

If the inspector can’t connect, try running the binary directly in a separate terminal to confirm it starts without errors.

Logs

The process appends JSON-RPC request/response lines to /tmp/mcp.jsonl.

tail -f /tmp/mcp.jsonl

Common issues

WARNING

• Connection refused: verify --prometheus-url and network reachability (Docker vs host networking).
• 401/403 from Prometheus: configure Basic Auth via env or flags.
• Time format: prefer RFC3339 (e.g., 2025-09-27T12:00:00Z) or Unix epoch seconds.