# Guardrail

A check, built into the harness or written into the instructions, that screens what goes in, what comes out, or what an agent tries to do.

Guardrails are an essential component of a robust AI system that has AI safety and AI security protections. Checks that run in code outside the model are much stronger than rules written in the instructions, which a model can ignore and an attacker can override. They can also be an important part of a product experience, ensuring that the system is behaving as intended and steering it back on track if not.

Also called: Safety filters, Content filters, Policy checks, Input/output validation

Related: Human oversight, Sandbox, Least privilege for AI

Source: https://redfinchadvisory.com/lexicon/guardrail (version 1.0, changed 2026-10-21)