What is MCP Debugger?

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MCP Debugger tests Model Context Protocol servers for spec compliance. Paste a server URL and get a report of the server's compliance with the MCP protocol.

This tool is built and maintained by Nate Barbettini, author of OIDC Debugger and a contributor to the MCP specification.

Grading reference

MCP Debugger assigns a letter grade (A through F) to summarize how well a server adheres to the MCP protocol. Use it as a quick signal, then review the detailed checks for specifics.

A — Clean pass
No failures or warnings, and the server reports a recent supported MCP protocol version.
B — Mostly works, minor nits
No failures, but at least one warning.
C — Some things work but spec gaps exist
One or more failures (often tied to a capability the server reported).
D — Major implementation problems
Most MCP clients will struggle (e.g. deprecated/unknown protocol version, auth issues, ping fails).
F — Unusable
Clients can't connect or core checks fail (network/DNS, invalid JSON/JSON-RPC, terminal auth discovery failures).

Open-source acknowledgments

MCP Debugger uses and extends the server side of the official MCP conformance suite, an open-source test suite maintained by the MCP team.

MCP Debugger is also built with the following open-source projects: