Whether the application is up and its database answers

Public: no session and no bearer; what an uptime monitor asks. 200 { status: "ok", db: "ok", commit } when one database round-trip succeeds within three seconds — commit is the build the deployment runs, null outside a platform build. 503 SERVICE_UNAVAILABLE (Database unreachable) with Retry-After when it does not; the same 503 when the rate limiter is unavailable, because every other route is refusing for that reason too. Never cached. 120 requests a minute per network address.