Validators

PII detection, toxicity, format (JSON schema), factual grounding, custom regex, competitor mentions. 60+ built-in.

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Reask on failure

Validator fails → framework re-prompts LLM with specific failure info. Iterate up to N times. Falls back to human if unresolved.

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Guardrails Hub

Marketplace of community validators. Contribute + reuse. Analogous to pre-commit hooks.

Rail spec

YAML/XML spec of validators + reasks per output field. Version-controlled.