What Is an Idempotency Key?

An idempotency key is a unique token a client attaches to a request so the server performs the operation at most once, even if the request is retried after a timeout or a network failure. For payments it is the difference between a safe retry and a double charge. Autonomous agents retry aggressively and without a human to notice a duplicate, so an idempotency key on every state-changing call is a baseline requirement for agent-initiated money movement.

Guarantee

At-most-once execution under retries

Prevents

Double charges on a retried payment

Agent relevance

Agents retry without human oversight

Safe retries for machines

A network failure leaves a client unsure whether a request succeeded. A human pauses and checks; an agent retries. Without idempotency, that retry can charge twice, place two orders, or send two payments. With it, the server recognises the repeated key and returns the original result instead of acting again.

It is unglamorous and load-bearing: agent-initiated commerce is a stream of retried, unattended requests, and idempotency is what keeps that stream from doing damage.