Idempotency

Idempotency is the property that performing the same operation more than once has the same effect as performing it once, preventing duplicate side effects from retries.

In payment and agent systems, an idempotency key lets a client safely retry a request — after a timeout or network error — without charging twice or repeating an action.

It is essential where agents take real actions, since retries and failures are common and a duplicated action can be costly.