What is MCP Debugger?
Test a server →MCP Debugger tests Model Context Protocol servers for spec compliance. Paste a server URL and get an independent report of how it behaves on the wire.
This tool is built and maintained by Nate Barbettini, author of OIDC Debugger and a contributor to the MCP specification.
Grading reference
The letter grade is a quick signal, not the whole diagnosis. Use it to orient yourself, then inspect the checks and evidence in the report.
- AClean pass
No failures or warnings, and the server reports a recent supported MCP protocol version.
- BMostly works
No failures, but at least one warning.
- CSpec gaps exist
One or more failures (often tied to a capability the server reported).
- DMajor problems
Most MCP clients will struggle (e.g. deprecated/unknown protocol version, auth issues, ping fails).
- FUnusable
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, maintained by the MCP team. It is also built with the projects below.
- Next.jsReact framework (web UI)
- ReactUI library
- HonoProxy backend framework
- Tailwind CSSUtility-first CSS
- Framer MotionAnimations
- LucideIcons
- ZustandState management
- ZodSchema validation
- MCP TypeScript SDKOfficial MCP client library
- VitestUnit testing