Idempotent API
In plain terms
An API where repeating a request has the same effect as one call.
Going deeper
Idempotent API operations can be safely retried without causing duplicate side effects, crucial for handling network failures. PUT and DELETE are naturally idempotent.
Under the hood
Idempotency keys make POST safe to retry; vital for payments and at-least-once delivery.
Examples
Payment retries, PUT/DELETE, idempotency-key headers, reliable APIs.
Think of it like...
Like a 'set thermostat to 70' command: sending it twice changes nothing extra.