Idempotency

Definition

An operation is idempotent if running it multiple times produces the same outcome as running it once. In API design, idempotent endpoints accept an idempotency key from the client so retries (due to network failures, timeouts or duplicate clicks) don't cause duplicate side effects — most importantly, duplicate payments, double orders or duplicate emails. Stripe, Razorpay and most payment providers require idempotency keys for write operations.

Why it matters

Network failures and retries are inevitable. Without idempotency, those failures translate to duplicate charges, duplicate orders and duplicate database rows. Idempotency is the single most-overlooked correctness feature in early-stage APIs.

See also