# ASSERTS
Expression-based checks for response or error data.
## When to use
- Prefer for resilient checks that survive minor payload changes
- Use alone or with `RESPONSE with_asserts` / `ERROR with_asserts`
## Minimal example
```gctf
--- ASSERTS ---
.status == "ok"
@len(.items) > 0
@has_header("x-request-id")
```
## Rules
- Each line is evaluated as a boolean expression
- Start with high-signal checks first (status, IDs, required fields)
## Related
- [Assertions API Reference](../api/assertions)