Guardrail

Also known as: output filter, safety rail

A guardrail is a component that intercepts, scores, or blocks model inputs or outputs that violate defined policies — such as requests for harmful content, personally identifiable information leakage, or off-topic responses. Guardrails may be implemented as classifiers, rule-based filters, or a secondary LLM call that reviews the primary model's output before it reaches the user. Evaluating guardrail effectiveness requires both pass-rate testing on legitimate inputs and adversarial testing to measure bypass resistance.