A Rails engine that adds structured, pluggable health check endpoints to any Rails app. Includes 11 built-in checks (database, cache, Redis, SMTP, Sidekiq, SolidQueue, GoodJob, Resque, disk, memory, HTTP), parallel execution via Concurrent::Future, result caching, Prometheus metrics, check groups, per-environment toggling, boot-time validation, and a Prometheus-compatible /metrics endpoint. Drop-in replacement for OkComputer.