# Concepts

Read these pages to understand how cronpad behaves under load and under failure, not just how to use it.

- [How cronpad works](how-cronpad-works.md): the components inside the binary and how a job becomes an HTTP request.
- [Jobs, runs and attempts](jobs-runs-attempts.md): the data model and every state a job or run can be in.
- [Delivery guarantees](delivery-guarantees.md): at-least-once delivery, idempotency, what "on time" means, and when duplicates can happen.
- [Scheduling engine](scheduling-engine.md): the SQLite queue, its atomic transactions and the claim loop, in detail.
- [Storage](storage.md): why SQLite, what each of the three files holds, and how far one node scales.