No response within the deadline, repeatedly. Like a server error this can be weather, so most are held for a second observation before being confirmed - and a timeout is worse for an agent than a refusal, because it spends the deadline before learning anything.
263 records across 208 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.