"Return JSON only" doesn't force JSON. Here's what actually forces it.

You have a judge LLM in your pipeline. You've told it: "Return JSON only. No preamble, no explanation. Just the JSON object." It works great in testing. It works great in staging. Then in production it returns: Sure! Here's my evaluation of the response: { "score" : 4 , "reason" : "The answer is mostly correct but..." } Your json.loads() throws. Your pipeline catches nothing. Downstream code receives None and keeps running. Your evaluation scores are silently wrong for the next 200 requests befo