Idempotency

A property of an operation where running it once or many times gives the same end result, so repeating it after a failure or duplicate does no extra harm.

An operation is idempotent if repeating it does not change the outcome after the first time. Setting a status to "paid" is idempotent. Adding 10 to a balance is not: doing it twice adds 20.

This matters because networks and automations repeat things. A webhook may be delivered twice, a retry logic attempt may run again after a timeout that actually succeeded, and a user may double-click. If the operation is not safe to repeat, you get duplicate orders, double charges or repeated emails.

Common techniques: send an idempotency key with each request so the receiver can recognize and ignore a repeat, use unique constraints in the database so a duplicate insert fails, and check whether the work is already done before doing it. It pairs naturally with error handling and helps avoid a race condition causing duplicates.

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