18089 of the MCP registry's 54142 entries, read on 2026-11-01, ship only as an installable package. Nothing is installed to check one: the package registry's own document says whether the package exists and whether the exact version an entry declares is published. These are the entries where it does not.
258 records across 164 subjects, observed 2026-09-10. Every one carries a check you can run in a single request.
All subjects · the whole registry, machine-readable
Asking about something not listed here, before you use it — one request, no key: GET https://apidefects.com/check?tool=<identity>. never_examined is an answer too, and it is not a clean bill of health.
This is not a list of good APIs or bad ones. It is a list of observations, each dated and each disprovable in one request. Absence from it means an operation was not examined, not that it is fine.