Treat AI Agent Tools Like Public APIs to Prevent Duplicate Actions

A developer's first production AI agent issued the same refund three times after a payment API returned a 502 error and the model retried the call. The root cause was a missing idempotency key, a bug familiar from standard HTTP client code rather than a language model problem. The article argues that the model should be treated as an unpredictable API caller, so tools need the same safeguards as public APIs, including versioning, timeouts, idempotency, scoped credentials, and rate limits. It recommends classifying every tool as read, write, or destructive, with that classification enforced in code rather than documentation. The author also advises generating idempotency keys in the application, since models will retry calls for many reasons.