The Tool Description That Rotted While Your Agent Kept Calling It
Your agent has been quietly wrong for six months and your error rate looks fine. The underlying API shipped a renamed error code, made one optional field required, and started rejecting calls without an idempotency header. The tool description in your agent's system prompt — pasted from a Notion page in Q4 of last year — describes none of this. The agent keeps calling the old shape, the orchestration layer keeps catching the failure and retrying with the same broken arguments, and the only signal in your telemetry is a slightly elevated retry count that nobody on call has the context to investigate.
Tool descriptions are interface contracts. They age the moment the underlying API does. And unlike a typed SDK, they break silently — the model just makes worse calls.
