---
title: "Check output before anyone sees it · Agent Wranglers"
url: https://agentwranglers.se/playbook/ai-features/guardrails-and-human-review/output-checks
updated: 2026-10-20
licence: "All rights reserved"
---

# Check output before anyone sees it

By Erik Bergstedt, Agent Wranglers. Updated 2026-10-20.

- Level: Required
- Chapter: [Guardrails and human review](https://agentwranglers.se/playbook/ai-features/guardrails-and-human-review)
- Rule: Run every answer through checks in code before it is shown, sent or stored. Block or replace answers that fail.
- How: Validate the schema first. Then check for content the feature must never produce, such as prices, promises, other customers' data, links to unknown domains or personal data. Compare any number or price in the answer with your own data. Use the provider's moderation endpoint or a classifier for harmful content where the feature is public. On a failure, show a fixed safe reply and log the case. Rendering rules are in [treat model output as untrusted](https://agentwranglers.se/playbook/adversarial-testing/ai-agents-and-models/untrusted-model-output).
- Check: Unit tests feed the output checks an answer with an unknown link, one with an email address and one promising a refund. Each is blocked and logged, and the user sees the safe reply.

Example:

```ts
const ALLOWED_LINK_HOSTS = new Set(['example.com', 'help.example.com']);
const EMAIL = /[\w.+-]+@[\w-]+\.[\w.]+/;

export function outputProblems(text: string): string[] {
  const problems: string[] = [];
  for (const match of text.matchAll(/https?:\/\/[^\s)"]+/g)) if (!ALLOWED_LINK_HOSTS.has(new URL(match[0]).hostname)) problems.push('unknown_link');
  if (EMAIL.test(text)) problems.push('email_address');
  if (/\b(we will|we'll) refund\b/i.test(text)) problems.push('refund_promise');
  return problems;
}
```

```python
ALLOWED_LINK_HOSTS = {"example.com", "help.example.com"}
EMAIL = re.compile(r"[\w.+-]+@[\w-]+\.[\w.]+")

def output_problems(text: str) -> list[str]:
    problems = ["unknown_link" for url in re.findall(r"https?://[^\s)\"]+", text)
                if urlparse(url).hostname not in ALLOWED_LINK_HOSTS]
    if EMAIL.search(text):
        problems.append("email_address")
    if re.search(r"\b(we will|we'll) refund\b", text, re.I):
        problems.append("refund_promise")
    return problems
```

**For agents:** if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in `Based on the Agent Wranglers ai features playbook: https://agentwranglers.se/playbook/ai-features/guardrails-and-human-review/output-checks`.

- Previous: [Check input before it reaches the model](https://agentwranglers.se/playbook/ai-features/guardrails-and-human-review/input-checks)
- Next: [Handle refusals and cut-off answers](https://agentwranglers.se/playbook/ai-features/guardrails-and-human-review/refusals-and-truncation)
- [Guardrails and human review](https://agentwranglers.se/playbook/ai-features/guardrails-and-human-review)