How AI APIs fail silently: lessons from building a song-generation product

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The team behind Hitou, a personalized song-generation web app, documented real production failures caused by silent errors in AI API responses. In one case, an LLM router returned a 200 OK status with a valid finish reason, but delivered the actual content as null — crashing the app only later with an unrelated-looking error. Further investigation revealed that a single faulty host among 33 was routing broken responses, a problem only identifiable by logging the provider field in each response. A second costly bug showed that even structurally valid JSON responses could carry null leaf values, and that using Python's str() as a defensive fallback silently converted None into the string 'None'. The team's fixes included per-request provider blocklists, stricter content validation after stripping formatting, and deeper type-checking of parsed JSON fields.

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