Why Your Production LLM Prompt Keeps Failing (And How to Diagnose It in 4 Steps)

You ship a prompt. It works in the playground. Two weeks later, someone files a bug: the model is doing something completely wrong in a specific context. You read the prompt again. Nothing looks broken. So you rewrite it. The bug is gone - but now three other behaviors regressed. You fix those, and the cycle starts again. This is the most common failure mode in production LLM systems: debugging by intuition, fixing by rewrite. The problem isn't that the prompts are bad. The problem is there's no systematic way to diagnose why they're failing or where exactly the fix should go.