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MCP Inspector

The tool to reach for when another client says nothing at all.

Run it

npx @modelcontextprotocol/inspector

It opens a browser UI. Choose Streamable HTTP, then:

URL:     https://api.unlob.com/mcp
Header:  x-api-key: ulb_…

Connect. List Tools should show eleven.

What it is for

Every other MCP client fails the same way: an empty tool list and no error. The Inspector shows you the actual frames — the initialize result, the negotiated protocol version, the raw responses — so you find out which step failed instead of guessing.

The decision it gives you is binary and useful:

  • Inspector lists eleven tools → the server and your key are both fine. The problem is in the other client’s configuration.
  • Inspector fails too → it is the server, the key, or the network, and the frame it shows you says which.

Doing this first saves more time than any amount of re-reading a config file.

Call a tool

Pick web_search, set query to something, and run it. You will see both the text content block and the structuredContent — the same payload, parsed, for clients that can use it.

It is also the fastest way to read a tool’s schema while writing a prompt, since it renders inputSchema directly.

The stdio server

To inspect a locally running stdio server instead, choose STDIO and give it the command. Useful when self-hosting against a local index.

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