# Drift

The slow change of a website away from what a program was written against, until a step or a field stops matching.

Kaabist watches for drift in canary runs and production jobs: candidates that stop matching, fields that come back empty, values outside their usual range. A program that drifted sends program.drift_detected.

```
{
  "type": "program.drift_detected",
  "data": {
    "program": "prg_4kTz",
    "field": "price",
    "kind": "fill_rate_drop",
    "source": "statistics"
  }
}
```

## Related

- [Self-healing locators](/product/self-healing)
- [Monitor pages behind a login](/use-cases/monitor-behind-login)
- [Canary run](/glossary/canary-run)
- [Self-healing locator](/glossary/self-healing-locator)