# Idempotency

Every writing endpoint takes an Idempotency-Key, so a retry after a timeout never does the thing twice.

## How it works

Send `Idempotency-Key` with any POST, PUT or DELETE: a fresh value per request, up to 255 characters (a GUID is the usual choice). The first request runs and its answer is kept for 24 hours; a repeat with the same key and the same request replays that answer with `Idempotent-Replayed: true`; the same key with a different body or path is refused as `idempotency_conflict`; a repeat that arrives while the first is still running is refused as `idempotency_in_progress`. A 5xx is not kept, so a retry after one runs again. Keys are scoped to your account.

The pages of the endpoints that require a key say so; on the others the header is honoured when sent.

HTTP:

```http
Idempotency-Key: 6f1c2d3e-4b5a-4c6d-8e7f-9a0b1c2d3e4f
```