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# NSSystemExtensionUsageDescriptionKey

A message that tells the user why the app is trying to install a system extension bundle.

```
let NSSystemExtensionUsageDescriptionKey: String
```

## Discussion

This key is required for all system extensions except DriverKit extensions, and must be in the extension’s `Info.plist` file. Failure to include this key results in an error at activation time. For DriverKit extensions, use [`OSBundleUsageDescriptionKey`](/documentation/SystemExtensions/OSBundleUsageDescriptionKey) instead.

---

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