# Output guard

**Source:** https://promtable.com/glossary/output-guard

> An output guard is a deterministic check applied to a language model's response before it reaches the user — validating JSON shape, blocking unsafe content, refusing if confidence is low, or rewriting failures.

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An output guard is a deterministic check applied to a language model's response before it reaches the user — validating JSON shape, blocking unsafe content, refusing if confidence is low, or rewriting failures.

Output guards complement input guardrails by inspecting and gating model output. Common output guards in 2026: JSON-schema validation (reject malformed), safety classifier scan (block toxic / leaking PII), confidence threshold (refuse if the model self-reports low confidence), action authorisation (require human approval for destructive tool calls), and length / format checks. Layered output guards are the production norm for any LLM feature that takes real traffic. They turn "trust the model" into "verify the model".

## When to use

- Any production LLM feature.
- Agent loops where tool actions are destructive or expensive.

## Common mistakes

- Output guard that only blocks — provide a fallback path so users aren't stuck.
- No metrics on guard fires — you don't see degradation when guards start blocking real content.

## Related terms

- [guardrails](https://promtable.com/glossary/guardrails)
- [safety-classifier](https://promtable.com/glossary/safety-classifier)
- [json-mode](https://promtable.com/glossary/json-mode)
- [structured-output](https://promtable.com/glossary/structured-output)

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