Idempotency Keys for Unsafe Retries
Recall when and how to use idempotency keys for unsafe REST operations.
Core rule When should an unsafe POST require an idempotency key? When duplicate side effects are expensive and clients may retry after ambiguous failure. Payments, orders, invites, subscriptions, and sends are common candidates. Objection “Our frontend disables the button, so duplicates cannot happen.” Mobile checkout with network retries. Your line Button disabling reduces double-clicks, but it does not cover timeouts, SDK retries, app restarts, or users on multiple devices. UI-only protection ignores transport ambiguity. It moves the control to the server boundary where every client path converges. PUT vs POST key Which duplicate-control pattern fits? Do not use idempotency keys…
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