Stop trusting prompts for guarantees your system should enforce
Available_Witness581 · reddit · 2026-09-01
The author flags a common mistake in production LLM systems: treating prompt instructions as hard guarantees. Telling the model "always return valid JSON, age must be an integer" doesn't give you a type guarantee — it can still return "27" as a string. In a prototype that's a parsing bug; in production it can break workflows, branch execution incorrectly, or corrupt state several steps later. The core principle: prompts guide behavior, the system enforces constraints. Anything that must always be true shouldn't be protected by the prompt alone.
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