Idempotency key

An idempotency key is a unique value the caller attaches to a request with side effects, so the server can recognise a retry of the same operation and return the original result instead of executing it again.

In travel APIs, the canonical use is booking. A timeout after a booking request leaves the caller blind: did it succeed? With an idempotency key, the caller retries with the same key and gets a definitive answer, never a duplicate booking.

Two rules make the mechanism safe. A key must be unique per intent, never reused for a different booking. And the server must reject the same key arriving with a different body; on traveldistro this returns a 409 with the code IDEMPOTENCY_CONFLICT. For the full retry behaviour, see the guide on idempotency and the reliability page.