The Web Bluetooth API allows websites to communicate with Bluetooth devices.
What if I told you websites could communicate with nearby Bluetooth devices in a secure and privacy-preserving way? This way, heart rate monitors, singing lightbulbs, and even turtles could interact directly with a website.
Until now, the ability to interact with Bluetooth devices has been possible only for platform-specific apps. The Web Bluetooth API aims to change this and brings it to web browsers as well.
Before we start
This document assumes you have some basic knowledge of how Bluetooth Low Energy (BLE) and the Generic Attribute Profile work.
Even though the Web Bluetooth API specification is not finalized yet, the spec authors are actively looking for enthusiastic developers to try out this API and give feedback on the spec and feedback on the implementation.
A subset of the Web Bluetooth API is available in ChromeOS, Chrome for Android 6.0, Mac (Chrome 56) and Windows 10 (Chrome 70). This means you should be able to request and connect to nearby Bluetooth Low Energy devices, read/write Bluetooth characteristics, receive GATT Notifications, know when a Bluetooth device gets disconnected, and even read and write to Bluetooth descriptors. See MDN's Browser compatibility table for more information.
For Linux and earlier versions of Windows, enable the
#experimental-web-platform-features
flag in about://flags
.
Available for origin trials
In order to get as much feedback as possible from developers using the Web Bluetooth API in the field, Chrome has previously added this feature in Chrome 53 as an origin trial for ChromeOS, Android, and Mac.
The trial has successfully ended in January 2017.
Security requirements
To understand the security tradeoffs, I recommend the Web Bluetooth Security Model post from Jeffrey Yasskin, a software engineer on the Chrome team, working on the Web Bluetooth API specification.
HTTPS only
Because this experimental API is a powerful new feature added to the web, it is made available only to secure contexts. This means you'll need to build with TLS in mind.
User gesture required
As a security feature, discovering Bluetooth devices with
navigator.bluetooth.requestDevice
must be triggered by a user gesture such
as a touch or a mouse click. We're talking about listening to
pointerup
, click
, and touchend
events.
button.addEventListener('pointerup', function(event) {
// Call navigator.bluetooth.requestDevice
});
Get into the code
The Web Bluetooth API relies heavily on JavaScript Promises. If you're not
familiar with them, check out this great Promises tutorial. One more thing,
() => {}
are ECMAScript 2015 Arrow functions.
Request Bluetooth devices
This version of the Web Bluetooth API specification allows websites, running in the Central role, to connect to remote GATT Servers over a BLE connection. It supports communication among devices that implement Bluetooth 4.0 or later.
When a website requests access to nearby devices using
navigator.bluetooth.requestDevice
, the browser prompts user with a device
chooser where they can pick one device or cancel the request.
The navigator.bluetooth.requestDevice()
function takes a mandatory object that
defines filters. These filters are used to return only devices that match some
advertised Bluetooth GATT services and/or the device name.
Services filter
For example, to request Bluetooth devices advertising the Bluetooth GATT Battery Service:
navigator.bluetooth.requestDevice({ filters: [{ services: ['battery_service'] }] })
.then(device => { /* … */ })
.catch(error => { console.error(error); });
If your Bluetooth GATT Service is not on the list of the standardized Bluetooth GATT services though, you may provide either the full Bluetooth UUID or a short 16- or 32-bit form.
navigator.bluetooth.requestDevice({
filters: [{
services: [0x1234, 0x12345678, '99999999-0000-1000-8000-00805f9b34fb']
}]
})
.then(device => { /* … */ })
.catch(error => { console.error(error); });
Name filter
You can also request Bluetooth devices based on the device name being advertised
with the name
filters key, or even a prefix of this name with the namePrefix
filters key. Note that in this case, you will also need to define the
optionalServices
key to be able to access any services not included in a
service filter. If you don't, you'll get an error later when trying to access
them.
navigator.bluetooth.requestDevice({
filters: [{
name: 'Francois robot'
}],
optionalServices: ['battery_service'] // Required to access service later.
})
.then(device => { /* … */ })
.catch(error => { console.error(error); });
Manufacturer data filter
It is also possible to request Bluetooth devices based on the manufacturer
specific data being advertised with the manufacturerData
filters key. This key
is an array of objects with a mandatory Bluetooth company identifier key named
companyIdentifier
. You can also provide a data prefix that filters
manufacturer data from Bluetooth devices that start with it. Note that you will
also need to define the optionalServices
key to be able to access any services
not included in a service filter. If you don't, you'll get an error later when
trying to access them.
// Filter Bluetooth devices from Google company with manufacturer data bytes
// that start with [0x01, 0x02].
navigator.bluetooth.requestDevice({
filters: [{
manufacturerData: [{
companyIdentifier: 0x00e0,
dataPrefix: new Uint8Array([0x01, 0x02])
}]
}],
optionalServices: ['battery_service'] // Required to access service later.
})
.then(device => { /* … */ })
.catch(error => { console.error(error); });
A mask can also be used with a data prefix to match some patterns in manufacturer data. Check out the Bluetooth data filters explainer to learn more.
Exclusion filters
The exclusionFilters
option in navigator.bluetooth.requestDevice()
lets
you exclude some devices from the browser picker. It can be used to exclude
devices that match a broader filter but are unsupported.
// Request access to a bluetooth device whose name starts with "Created by".
// The device named "Created by Francois" has been reported as unsupported.
navigator.bluetooth.requestDevice({
filters: [{
namePrefix: "Created by"
}],
exclusionFilters: [{
name: "Created by Francois"
}],
optionalServices: ['battery_service'] // Required to access service later.
})
.then(device => { /* … */ })
.catch(error => { console.error(error); });
No filters
Finally, instead of filters
you can use the acceptAllDevices
key to show all
nearby Bluetooth devices. You will also need to define the optionalServices
key to be able to access some services. If you don't, you'll get an error later
when trying to access them.
navigator.bluetooth.requestDevice({
acceptAllDevices: true,
optionalServices: ['battery_service'] // Required to access service later.
})
.then(device => { /* … */ })
.catch(error => { console.error(error); });
Connect to a Bluetooth device
So what do you do now that you have a BluetoothDevice
? Let's connect to the
Bluetooth remote GATT Server which holds the service and characteristic
definitions.
navigator.bluetooth.requestDevice({ filters: [{ services: ['battery_service'] }] })
.then(device => {
// Human-readable name of the device.
console.log(device.name);
// Attempts to connect to remote GATT Server.
return device.gatt.connect();
})
.then(server => { /* … */ })
.catch(error => { console.error(error); });
Read a Bluetooth Characteristic
Here we connect to the GATT Server of the remote Bluetooth device. Now we want to get a Primary GATT Service and read a characteristic that belongs to this service. Let's try, for instance, to read the current charge level of the device's battery.
In the example ahead, battery_level
is the standardized Battery Level
Characteristic.
navigator.bluetooth.requestDevice({ filters: [{ services: ['battery_service'] }] })
.then(device => device.gatt.connect())
.then(server => {
// Getting Battery Service…
return server.getPrimaryService('battery_service');
})
.then(service => {
// Getting Battery Level Characteristic…
return service.getCharacteristic('battery_level');
})
.then(characteristic => {
// Reading Battery Level…
return characteristic.readValue();
})
.then(value => {
console.log(`Battery percentage is ${value.getUint8(0)}`);
})
.catch(error => { console.error(error); });
If you use a custom Bluetooth GATT characteristic, you may provide either the
full Bluetooth UUID or a short 16- or 32-bit form to
service.getCharacteristic
.
Note that you can also add a characteristicvaluechanged
event listener on a
characteristic to handle reading its value. Check out the Read Characteristic
Value Changed Sample to see how to optionally handle upcoming GATT
notifications as well.
…
.then(characteristic => {
// Set up event listener for when characteristic value changes.
characteristic.addEventListener('characteristicvaluechanged',
handleBatteryLevelChanged);
// Reading Battery Level…
return characteristic.readValue();
})
.catch(error => { console.error(error); });
function handleBatteryLevelChanged(event) {
const batteryLevel = event.target.value.getUint8(0);
console.log('Battery percentage is ' + batteryLevel);
}
Write to a Bluetooth Characteristic
Writing to a Bluetooth GATT Characteristic is as easy as reading it. This time, let's use the Heart Rate Control Point to reset the value of the Energy Expended field to 0 on a heart rate monitor device.
I promise there is no magic here. It's all explained in the Heart Rate Control Point Characteristic page.
navigator.bluetooth.requestDevice({ filters: [{ services: ['heart_rate'] }] })
.then(device => device.gatt.connect())
.then(server => server.getPrimaryService('heart_rate'))
.then(service => service.getCharacteristic('heart_rate_control_point'))
.then(characteristic => {
// Writing 1 is the signal to reset energy expended.
const resetEnergyExpended = Uint8Array.of(1);
return characteristic.writeValue(resetEnergyExpended);
})
.then(_ => {
console.log('Energy expended has been reset.');
})
.catch(error => { console.error(error); });
Receive GATT notifications
Now, let's see how to be notified when the Heart Rate Measurement characteristic changes on the device:
navigator.bluetooth.requestDevice({ filters: [{ services: ['heart_rate'] }] })
.then(device => device.gatt.connect())
.then(server => server.getPrimaryService('heart_rate'))
.then(service => service.getCharacteristic('heart_rate_measurement'))
.then(characteristic => characteristic.startNotifications())
.then(characteristic => {
characteristic.addEventListener('characteristicvaluechanged',
handleCharacteristicValueChanged);
console.log('Notifications have been started.');
})
.catch(error => { console.error(error); });
function handleCharacteristicValueChanged(event) {
const value = event.target.value;
console.log('Received ' + value);
// TODO: Parse Heart Rate Measurement value.
// See https://github.com/WebBluetoothCG/demos/blob/gh-pages/heart-rate-sensor/heartRateSensor.js
}
The Notifications Sample shows you to how to stop notifications with
stopNotifications()
and properly remove the added characteristicvaluechanged
event listener.
Disconnect from a Bluetooth Device
To provide a better user experience, you may want to listen for disconnection events and invite the user to reconnect:
navigator.bluetooth.requestDevice({ filters: [{ name: 'Francois robot' }] })
.then(device => {
// Set up event listener for when device gets disconnected.
device.addEventListener('gattserverdisconnected', onDisconnected);
// Attempts to connect to remote GATT Server.
return device.gatt.connect();
})
.then(server => { /* … */ })
.catch(error => { console.error(error); });
function onDisconnected(event) {
const device = event.target;
console.log(`Device ${device.name} is disconnected.`);
}
You can also call device.gatt.disconnect()
to disconnect your web app from the
Bluetooth device. This will trigger existing gattserverdisconnected
event
listeners. Note that it will NOT stop bluetooth device communication if another
app is already communicating with the Bluetooth device. Check out the Device
Disconnect Sample and the Automatic Reconnect Sample to dive deeper.
Read and write to Bluetooth descriptors
Bluetooth GATT descriptors are attributes that describe a characteristic value. You can read and write them to in a similar way to Bluetooth GATT characteristics.
Let's see for instance how to read the user description of the measurement interval of the device's health thermometer.
In the example below, health_thermometer
is the Health Thermometer service,
measurement_interval
the Measurement Interval characteristic, and
gatt.characteristic_user_description
the Characteristic User Description
descriptor.
navigator.bluetooth.requestDevice({ filters: [{ services: ['health_thermometer'] }] })
.then(device => device.gatt.connect())
.then(server => server.getPrimaryService('health_thermometer'))
.then(service => service.getCharacteristic('measurement_interval'))
.then(characteristic => characteristic.getDescriptor('gatt.characteristic_user_description'))
.then(descriptor => descriptor.readValue())
.then(value => {
const decoder = new TextDecoder('utf-8');
console.log(`User Description: ${decoder.decode(value)}`);
})
.catch(error => { console.error(error); });
Now that we've read the user description of the measurement interval of the device's health thermometer, let's see how to update it and write a custom value.
navigator.bluetooth.requestDevice({ filters: [{ services: ['health_thermometer'] }] })
.then(device => device.gatt.connect())
.then(server => server.getPrimaryService('health_thermometer'))
.then(service => service.getCharacteristic('measurement_interval'))
.then(characteristic => characteristic.getDescriptor('gatt.characteristic_user_description'))
.then(descriptor => {
const encoder = new TextEncoder('utf-8');
const userDescription = encoder.encode('Defines the time between measurements.');
return descriptor.writeValue(userDescription);
})
.catch(error => { console.error(error); });
Samples, demos and codelabs
All Web Bluetooth samples below have been successfully tested. To enjoy these samples to their fullest, I recommend you install the [BLE Peripheral Simulator Android App] which simulates a BLE peripheral with a Battery Service, a Heart Rate Service, or a Health Thermometer Service.
Beginner
- Device Info - retrieve basic device information from a BLE Device.
- Battery Level - retrieve battery information from a BLE Device advertising Battery information.
- Reset Energy - reset energy expended from a BLE Device advertising Heart Rate.
- Characteristic Properties - display all properties of a specific characteristic from a BLE Device.
- Notifications - start and stop characteristic notifications from a BLE Device.
- Device Disconnect - disconnect and get notified from a disconnection of a BLE Device after connecting to it.
- Get Characteristics - get all characteristics of an advertised service from a BLE Device.
- Get Descriptors - get all characteristics' descriptors of an advertised service from a BLE Device.
- Manufacturer Data Filter - retrieve basic device information from a BLE Device that matches manufacturer data.
- Exclusion Filters - retrieve basic device information from a BLE Device featuring basic exclusion filters.
Combining multiple operations
- GAP Characteristics - get all GAP characteristics of a BLE Device.
- Device Information Characteristics - get all Device Information characteristics of a BLE Device.
- Link Loss - set the Alert Level characteristic of a BLE Device (readValue & writeValue).
- Discover Services & Characteristics - discover all accessible primary services and their characteristics from a BLE Device.
- Automatic Reconnect - reconnect to a disconnected BLE device using an exponential backoff algorithm.
- Read Characteristic Value Changed - read battery level and be notified of changes from a BLE Device.
- Read Descriptors - read all characteristic's descriptors of a service from a BLE Device.
- Write Descriptor - write to the descriptor "Characteristic User Description" on a BLE Device.
Check out our curated Web Bluetooth Demos and official Web Bluetooth Codelabs as well.
Libraries
- web-bluetooth-utils is a npm module that adds some convenience functions to the API.
- A Web Bluetooth API shim is available in noble, the most popular Node.js BLE central module. This allows you to webpack/browserify noble without the need for a WebSocket server or other plugins.
- angular-web-bluetooth is a module for Angular that abstracts away all the boilerplate needed to configure the Web Bluetooth API.
Tools
- Get Started with Web Bluetooth is a simple Web App that will generate all the JavaScript boilerplate code to start interacting with a Bluetooth device. Enter a device name, a service, a characteristic, define its properties and you're good to go.
- If you're already a Bluetooth developer, the Web Bluetooth Developer Studio Plugin will also generate the Web Bluetooth JavaScript code for your Bluetooth device.
Tips
A Bluetooth Internals page is available in Chrome at
about://bluetooth-internals
so that you can inspect everything about nearby
Bluetooth devices: status, services, characteristics, and descriptors.
I also recommend checking out the official How to file Web Bluetooth bugs page as debugging Bluetooth can be hard sometimes.
What's next
Check the browser and platform implementation status first to know which parts of the Web Bluetooth API are currently being implemented.
Though it's still incomplete, here's a sneak peek of what to expect in the near future:
- Scanning for nearby BLE advertisements
will happen with
navigator.bluetooth.requestLEScan()
. - A new
serviceadded
event will track newly discovered Bluetooth GATT Services whileserviceremoved
event will track removed ones. A newservicechanged
event will fire when any characteristic and/or descriptor gets added or removed from a Bluetooth GATT Service.
Show support for the API
Are you planning to use the Web Bluetooth API? Your public support helps the Chrome team prioritize features and shows other browser vendors how critical it is to support them.
Send a tweet to @ChromiumDev using the hashtag
#WebBluetooth
and let us know where and how you are using it.
Resources
- Stack Overflow
- Chrome Feature Status
- Chrome Implementation bugs
- Web Bluetooth spec
- Spec Issues on GitHub
- BLE Peripheral Simulator App
Acknowledgements
Thanks to Kayce Basques for reviewing this article. Hero image by SparkFun Electronics from Boulder, USA.