# Guardrails

**Source:** https://promtable.com/glossary/guardrails

> Guardrails are deterministic checks layered around a language model to prevent unsafe, off-topic, or non-compliant outputs from reaching the user.

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Guardrails are deterministic checks layered around a language model to prevent unsafe, off-topic, or non-compliant outputs from reaching the user.

Guardrails sit on the input or output side of a model call. Input guardrails (PII detection, prompt injection scanners, policy classifiers) reject or rewrite the request before the model sees it. Output guardrails (toxicity checks, JSON validators, fact-checkers, profanity filters) inspect the model's response and either pass, rewrite, or refuse. Frameworks: Guardrails AI, NeMo Guardrails, Llama Guard, OpenAI Moderation, Lakera. In production every LLM-facing surface in 2026 has at least lightweight guardrails — the question is which ones.

## When to use

- Any user-facing AI feature.
- Regulated industries (finance, healthcare, education).

## Common mistakes

- Relying only on prompt instructions for safety — easily bypassed.
- Using guardrails as a substitute for an evals system.

## Related terms

- [system-prompt](https://promtable.com/glossary/system-prompt)
- [hallucination](https://promtable.com/glossary/hallucination)
- [agent](https://promtable.com/glossary/agent)

*Last updated: 2026-06-01*
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Original page: https://promtable.com/glossary/guardrails
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