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# CBDescriptor

An object that provides further information about a remote peripheral’s characteristic.

```
class CBDescriptor
```

## Overview

[`CBDescriptor`](/documentation/CoreBluetooth/CBDescriptor) and its subclass [`CBMutableDescriptor`](/documentation/CoreBluetooth/CBMutableDescriptor) represent a descriptor of a peripheral’s characteristic. In partcular, [`CBDescriptor`](/documentation/CoreBluetooth/CBDescriptor) objects represent the descriptors of a remote peripheral’s characteristic. Descriptors provide further information about a characteristic’s value. For example, they may describe the value in human-readable form and describe how to format the value for presentation purposes. Characteristic descriptors also indicate whether a characteristic’s value indicates or notifies a client (a central) when the value of the characteristic changes.

[`CBUUID`](/documentation/CoreBluetooth/CBUUID) details six predefined descriptors and their corresponding value types. [`CBDescriptor`](/documentation/CoreBluetooth/CBDescriptor) lists the predefined descriptors and the [`CBUUID`](/documentation/CoreBluetooth/CBUUID) constants that represent them.

|Descriptor type                    |Descriptor constant                                                                                        |
|-----------------------------------|-----------------------------------------------------------------------------------------------------------|
|Characteristic extended properties |``doc://com.apple.corebluetooth/documentation/CoreBluetooth/CBUUIDCharacteristicExtendedPropertiesString`` |
|Characteristic user description    |``doc://com.apple.corebluetooth/documentation/CoreBluetooth/CBUUIDCharacteristicUserDescriptionString``    |
|Client characteristic configuration|``doc://com.apple.corebluetooth/documentation/CoreBluetooth/CBUUIDClientCharacteristicConfigurationString``|
|Server characteristic configuration|``doc://com.apple.corebluetooth/documentation/CoreBluetooth/CBUUIDServerCharacteristicConfigurationString``|
|Characteristic format              |``doc://com.apple.corebluetooth/documentation/CoreBluetooth/CBUUIDCharacteristicFormatString``             |
|Characteristic aggregate format    |``doc://com.apple.corebluetooth/documentation/CoreBluetooth/CBUUIDCharacteristicAggregateFormatString``    |

## Topics

### Identifying a Descriptor

[`characteristic`](/documentation/CoreBluetooth/CBDescriptor/characteristic)

The characteristic to which this descriptor belongs.

### Accessing Descriptor Data

[`value`](/documentation/CoreBluetooth/CBDescriptor/value)

The value of the descriptor.


---

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