LLM guardrails are a separate distrust layer, not a refusals habit
Ashamed_Stodach_5657 · reddit · 2026-09-03
An engineer shares the mental model that made LLM guardrails click: in real deployments, guardrails aren't about the model refusing things — they're a separate layer that doesn't trust the model at all. His structure: (1) inbound checks screen every prompt for injection attempts, policy violations and PII before it reaches the model; (2) the model runs; (3) outbound checks review responses for leaks, fabricated claims and policy violations before users see them. Key insight: this must be its own layer, not a system prompt — prompts are merely suggestions a model can be talked into skipping, while an external check actually enforces rules, and pure keyword matching is insufficient since politely phrased violations slip through. His open question is latency: every check adds time before the user gets a response, and he asks how others balance that tradeoff.
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