Use the MCP inspector to test stdio MCP servers interactively

2026-03-03 (7m ago)2 views

#mcp#go#debugging

I was building a Go MCP server using mcp-go and wanted to test it without wiring it up to Claude Desktop first. The problem is that stdio MCP servers just hang when you run them directly in a terminal — they're waiting for the MCP protocol handshake on stdin, so you get nothing useful.

Turns out there's an official inspector tool from the MCP project:

bunx @modelcontextprotocol/inspector /full/path/to/your/binary

(or npx if you're not on bun)

This spins up a local proxy and opens a web UI at http://localhost:6274 where you can:

• browse all tools the server registered
• fill in arguments and call them interactively
• see the raw JSON responses

A couple of gotchas I hit:

Pass the full path to the binary. The inspector spawns the process itself (it's not a shell), so it won't find the binary if you just give it a bare name like my-mcp-server. I got ENOENT until I used the absolute path.

mcp-go doesn't ship an inspector. I tried go run github.com/mark3labs/mcp-go/cmd/mcpinspector@latest based on a guess and got a "does not contain package" error. The inspector is a separate npm package — @modelcontextprotocol/inspector — maintained by the MCP project, not by individual SDK authors.

The inspector is genuinely useful: much faster feedback loop than registering in Claude Desktop and restarting it every time you change something.