MCP server inspector

This MCP server inspector connects to a public MCP server URL, lists its tools, input schemas, and capabilities, and notes where inputs are unbounded or names suggest write actions. It reports what it observed. It does not score or certify a server.

No sign-up. Runs in your browser. Last reviewed November 4, 2026 by the Builderz team.

How it works

What it sends, in order

One POST with the initialize request, then the initialized notification, then tools/list. If the server announces resources or prompts, it also sends resources/list and prompts/list. The total is capped at six requests.

What it reads

Server name and version, the protocol version, the capabilities, each tool name, description, and inputSchema, and the response headers. Replies may be JSON or an event stream. Everything is parsed as data and shown as text.

What the findings mean and do not mean

Observed, not observed, and not applicable describe what the protocol exposed in these few requests. A finding is an observation, not a vulnerability. Not observed can mean the signal is absent from the protocol, not that the control is absent from the server.

The auth boundary

The inspector only tries an anonymous initialize. It does not accept tokens, keys, or headers from you. If the server answers 401 or 403 it says so and stops.

What is logged

Nothing beyond the request count. The URL and the results are not stored, and the response is not cached.

Questions about this tool

Why does it say the server requires authentication?

The server answered the anonymous initialize request with 401 or 403. This tool does not take tokens, so it stops there. Use the official MCP Inspector locally for servers that need credentials.

Why does my local server not work?

The check runs from a server on the public internet. It only reaches https URLs on public DNS, so localhost, private addresses, and plain http are refused.

Is a finding a vulnerability?

No. A finding is an observation from the protocol, such as a string parameter without maxLength. Whether it matters depends on what the tool does and who can call it.

Does it store my URL?

No. The request is handled and discarded, and the response is marked no-store. Only the number of requests sent is reported back to you.