Why 200 OK Is the Most Dangerous Response in Agent Production

The scary failures are not always the ones that crash. Sometimes everything looks fine. The API returns 200 OK . The logs are clean. The workflow completes. No alert fires. And the result is wrong. That is a much worse failure mode than a timeout or a hard error, because nothing tells you to go look. The system says success. The output just quietly drifts away from reality. This is starting to show up more in agent systems than in normal software. A normal service usually fails loudly. Bad input throws an exception. A downstream service times out. A database call returns an error. Something breaks in a way people know how to detect. Agents can fail differently. They can keep going. They can produce something that looks plausible, structured, and complete while being based on the wrong state, the wrong tool result, or the wrong interpretation of the task. That is where 200 OK gets dangerous. Three examples 1. The tool call "worked" An agent is supposed to pull data from a system and sum