A UUID is a Universally Unique Identifier. For BLE devices, the 128 bit UUID represents a specific profile, service or data type. It is guaranteed to be unique across all space and all time according to the Bluetooth 4.2 spec. Each UUID is a 128 bit value. Some examples are:


You will see that the UUID is divided up into sections with a hyphen. the hyphen is not part of the UUID – it is used to make them a little more readable for humans. Hyphens in a UUID are generally ignored by software.

A range of UUIDs is defined by the Bluetooth SIG. These are all formed from the BluetoothBaseUUID of


The second half of the first section (00000000-) represents a 16 bit number that can be used as a shorthand for a reserved, pre-defined UUID. That allows you to write only the shorthand portion rather than the full UUID value. If your application can use one of these pre-defines UUIDs then it will save some typing at least. If you come across mention of a BLE UUID and it only has four digits, it is a 16-bit UUID and should be interpreted as part of an entire 128-bit UUID. For example, the Battery Service UUID may be written 1815 or 0x1815 but the full UUId is actually

Next, some predefined 16-bit UUIDs are described. After that, there is some information on creating your own 128-bit UUIDs.

Predefined GATT Service UUIDs

Some of the 16 bit identifiers are used to define well-known services. GATT Services are collections of characteristics and relationships to other services that encapsulate the behaviour of part of a device. A list can be found here Some examples include (notice that services appear to all be of the form 0x1---):

Name Uniform Type Identifier Assigned Number
Generic Access org.bluetooth.service.generic_access 0x1800
Alert Notification Service org.bluetooth.service.alert_notification 0x1811
Automation IO org.bluetooth.service.automation_io 0x1815
Battery Service org.bluetooth.service.battery_service 0x180F
Binary Sensor GATT Service UUID 0x183B
Current Time Service org.bluetooth.service.current_time 0x1805
Device Information org.bluetooth.service.device_information 0x180A
Emergency Configuration GATT Service UUID 0x183C
Environmental Sensing org.bluetooth.service.environmental_sensing 0x181A
Generic Attribute org.bluetooth.service.generic_attribute 0x1801
Human Interface Device org.bluetooth.service.human_interface_device 0x1812
Immediate Alert org.bluetooth.service.immediate_alert 0x1802
Indoor Positioning org.bluetooth.service.indoor_positioning 0x1821
Link Loss org.bluetooth.service.link_loss 0x1803
Location and Navigation org.bluetooth.service.location_and_navigation 0x1819
Object Transfer Service org.bluetooth.service.object_transfer 0x1825
Transport Discovery org.bluetooth.service.transport_discovery 0x1824
Tx Power org.bluetooth.service.tx_power 0x1804
User Data org.bluetooth.service.user_data 0x181C

Predefined Characteristic UUIDs

Characteristics are defined attribute types that contain a single logical value. There are a large number of predefined characteristics in the standard. You can find a list at (notice that characteristics appear to all be of the form 0x2---)

Name Uniform Type Identifier Assigned Number
Alert Category ID org.bluetooth.characteristic.alert_category_id 0x2A43
Alert Level org.bluetooth.characteristic.alert_level 0x2A06
Alert Status org.bluetooth.characteristic.alert_status 0x2A3F
Altitude org.bluetooth.characteristic.altitude 0x2AB3
Analog org.bluetooth.characteristic.analog 0x2A58
Analog Output org.bluetooth.characteristic.analog_output 0x2A59
Battery Level org.bluetooth.characteristic.battery_level 0x2A19
Current Time org.bluetooth.characteristic.current_time 0x2A2B
Digital 0x2A56
Digital Output org.bluetooth.characteristic.digital_output 0x2A57
Firmware Revision String org.bluetooth.characteristic.firmware_revision_string 0x2A26
First Name org.bluetooth.characteristic.first_name 0x2A8A
Device Name 0x2A00
Reconnection Address 0x2A03
Service Changed org.bluetooth.characteristic.gatt.service_changed 0x2A05
Hardware Revision String org.bluetooth.characteristic.hardware_revision_string 0x2A27
Humidity org.bluetooth.characteristic.humidity 0x2A6F
Last Name org.bluetooth.characteristic.last_name 0x2A90
Latitude org.bluetooth.characteristic.latitude 0x2AAE
Longitude org.bluetooth.characteristic.Longitude 0x2AAF
Manufacturer Name String org.bluetooth.characteristic.manufacturer_name_string 0x2A29
Measurement Interval org.bluetooth.characteristic.measurement_interval 0x2A21
Model Number String org.bluetooth.characteristic.model_number_string 0x2A24
Pressure org.bluetooth.characteristic.pressure 0x2A6D
Rainfall org.bluetooth.characteristic.rainfall 0x2A78
Serial Number String org.bluetooth.characteristic.serial_number_string 0x2A25
Service Required org.bluetooth.characteristic.service_required 0x2A3B
Software Revision String org.bluetooth.characteristic.software_revision_string 0x2A28
String org.bluetooth.characteristic.string 0x2A3D
System ID org.bluetooth.characteristic.system_id 0x2A23
Temperature org.bluetooth.characteristic.temperature 0x2A6E
Temperature Celsius org.bluetooth.characteristic.temperature_celsius 0x2A1F
Temperature Fahrenheit org.bluetooth.characteristic.temperature_fahrenheit 0x2A20
Time Broadcast org.bluetooth.characteristic.time_broadcast 0x2A15

User Defined UUIDs

If you want to create your own custom services, then you will need to create your own UUIDs. So long as the UUID that you create does not end in the BluetoothBaseUUID value, you are free to pick anything you like. The available range of values is so large that there is almost zero chance (about 1 in 10^39) of accidentally duplicating an existing value. there are online generators for this. Version 1 UUIDs are based on the time and your computer’s mac address and version 4 UUIDs are based on a 128 bit random number generator. Try or

If you want to use a number of related services and characteristics, you might want to generate a base UUID and then use the upper four bytes to distinguish them For example, if you generated this UUID
then you might zero the upper bytes to get a base UUID of
So that your own services and characteristics could be represented there. If it suited your purpose, it might be convenient to use the first two bytes to represent services and the second two bytes to represent characteristics. That would make it easier to see what was related to what. There are no rules for this though. Suppose for example, you had a robot that had a service could report its position and a service that could report its IMU readings. You might conceivably come up with a scheme something like this:

UUID Purpose
27810000-4786-42e7-bd27-45257b2e988f Robot position service
27811701-4786-42e7-bd27-45257b2e988f Robot position X
27811702-4786-42e7-bd27-45257b2e988f Robot position Y
27811703-4786-42e7-bd27-45257b2e988f Robot position Z
27400000-4786-42e7-bd27-45257b2e988f Robot IMU service
27404301-4786-42e7-bd27-45257b2e988f Robot Gyro X
27404301-4786-42e7-bd27-45257b2e988f Robot Gyro X
27404301-4786-42e7-bd27-45257b2e988f Robot Gyro Z

Mandatory Identifiers

Every Bluetooth device MUST have a 48 bit identifier. This is equivalent to the MAC address used in ethernet networks. Unlike ethernet, there is no guarantee that these are unique or that they positively identify a device for all time. The mandatory Identifier is used to identify a device during communication exchanges. A device that is restarted may use a different identifier.