---
title: Output Check (NeMo Guardrail)
type: guardrail
provider: nvidia
category: safety
source: 'https://github.com/NVIDIA-NeMo/Guardrails'
license: Apache-2.0
tags:
  - guardrail
  - nemo
  - rails
  - colang
dateAdded: '2026-04-09'
featured: false
origin: official
language: en
description: >-
  flow self check output $allowed = await SelfCheckOutputAction if not $allowed
  if $system.config.enable_rails_exceptions send OutputRailException(messa
---

```coffee
flow self check output
  $allowed = await SelfCheckOutputAction

  if not $allowed
    if $system.config.enable_rails_exceptions
      send OutputRailException(message="Output not allowed. The output was blocked by the 'self check output' flow.")
    else
      bot refuse to respond
      abort
```