To connect to a nearby Bluetooth Low Energy (BLE) peripheral from a web page, run navigator.bluetooth.requestDevice() from a user action on a secure (HTTPS) page, select a device with the correct service permissions, connect to its GATT server, and then read, write, or subscribe to characteristics. The example below uses the standard Battery Service; replace its service and characteristic UUIDs with those exposed by your hardware.
Complete Web Bluetooth example
This page connects to a device that exposes the standard Battery Service and reads its battery percentage. Save it as index.html, serve it from HTTPS (or a browser-supported local development origin), and open it in a browser that implements Web Bluetooth.
<!doctype html>
<html lang="en">
<meta charset="utf-8">
<title>Web Bluetooth battery example</title>
<button id="connect" type="button">Connect Bluetooth device</button>
<output id="status" role="status">Disconnected</output>
<script>
const button = document.querySelector('#connect');
const status = document.querySelector('#status');
function setStatus(message) {
status.textContent = message;
}
async function connectToDevice() {
if (!window.isSecureContext) {
throw new Error('Web Bluetooth requires a secure context (HTTPS).');
}
if (!navigator.bluetooth) {
throw new Error('Web Bluetooth is unavailable in this browser.');
}
// This call must happen directly from the button click.
const device = await navigator.bluetooth.requestDevice({
filters: [{ services: ['battery_service'] }]
});
device.addEventListener('gattserverdisconnected', () => {
setStatus('Device disconnected');
});
setStatus(`Connecting to ${device.name || 'device'}…`);
const server = await device.gatt.connect();
const service = await server.getPrimaryService('battery_service');
const characteristic = await service.getCharacteristic('battery_level');
const value = await characteristic.readValue();
const percent = value.getUint8(0);
setStatus(`Battery: ${percent}%`);
return { device, server, characteristic, percent };
}
button.addEventListener('click', async () => {
button.disabled = true;
setStatus('Choose a device…');
try {
await connectToDevice();
} catch (error) {
setStatus(`${error.name || 'Error'}: ${error.message}`);
console.error(error);
} finally {
button.disabled = false;
}
});
</script>
</html>battery_service and battery_level work only when the selected peripheral actually implements those standard UUIDs. For a custom board, use the service and characteristic UUIDs documented by its firmware.
How the connection flow works
1. Check the execution environment
Web Bluetooth is restricted to secure contexts. Deploy the page over HTTPS. A browser may also expose navigator.bluetooth while a later policy, hardware, or permission check still prevents a connection, so feature detection is only the first guard.
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2. Request a device after a user gesture
requestDevice() opens the browser’s chooser and requires transient user activation, normally a button click or similar direct interaction. Do not call it automatically during page load or from a timer. The promise rejects if the user cancels, denies permission, or no matching device can be selected.
3. Choose filters and authorize services
A service filter is the safest usual choice because it limits the chooser to peripherals advertising a service you need:
const device = await navigator.bluetooth.requestDevice({
filters: [
{ services: ['battery_service'] },
{ namePrefix: 'Sensor-' , services: ['0000180f-0000-1000-8000-00805f9b34fb'] }
]
});Every service you will access after selection must be represented by a filter or by optionalServices. A name-only filter therefore needs optional service authorization:
const device = await navigator.bluetooth.requestDevice({
filters: [{ namePrefix: 'Sensor-' }],
optionalServices: ['battery_service', 'device_information']
});If you genuinely cannot identify a service in advance, acceptAllDevices: true shows any discoverable device, but you still must list every service you plan to access in optionalServices:
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optionalServices: ['battery_service']
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4. Connect to GATT and obtain a characteristic
The selected device exposes a GATT server. Connect, retrieve the primary service, and then retrieve the characteristic by its assigned name or UUID:
const server = await device.gatt.connect();
const service = await server.getPrimaryService('battery_service');
const level = await service.getCharacteristic('battery_level');Connection is asynchronous and can fail after the chooser succeeds. Keep the resulting device object so you can respond to disconnects or reconnect after an interruption.
Reading, writing, and notifications
Read a value
readValue() returns a DataView. Decode it according to the peripheral’s protocol, including byte order and field length:
const value = await characteristic.readValue();
const firstByte = value.getUint8(0);
const littleEndianNumber = value.getUint16(0, true);Write a command
A writable characteristic accepts a Uint8Array. The device’s documentation must define the command bytes; the following is only a transport pattern:
const command = new Uint8Array([0x01, 0x00]);
await characteristic.writeValue(command);Some devices distinguish write-with-response from write-without-response. Use the method supported by the characteristic and firmware, and keep payloads within the device’s permitted size.
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Subscribe to notifications
For streaming sensor data, start notifications and decode each incoming DataView:
await characteristic.startNotifications();
characteristic.addEventListener('characteristicvaluechanged', event => {
const value = event.target.value;
console.log('Received byte:', value.getUint8(0));
});Call stopNotifications() when the page no longer needs updates. Notifications are not a substitute for reconnect logic: a disconnect ends the GATT session.
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device.addEventListener('gattserverdisconnected', async () => {
console.log('Disconnected');
// Reconnect only in response to an appropriate application action or policy.
try {
const server = await device.gatt.connect();
console.log('Reconnected', server.connected);
} catch (error) {
console.error('Reconnect failed', error);
}
});Always treat a reconnect as a new session: reacquire services and characteristics and restart notifications.
Availability, permissions, and iframes
getAvailability() is only a hint
if (navigator.bluetooth?.getAvailability) {
const possiblyAvailable = await navigator.bluetooth.getAvailability();
console.log('Bluetooth may be available:', possiblyAvailable);
}A false result can reflect adapter state, browser settings, or policy. A true result does not guarantee that the adapter is powered, a peripheral is discoverable, the chooser will return a device, or GATT operations will succeed. Handle errors from the real request and connection path.
Permissions Policy
The bluetooth Permissions Policy defaults to self. A top-level page normally needs no extra markup. A cross-origin iframe needs both a response policy that authorizes the frame’s origin and an iframe attribute such as:
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<iframe src="https://app.example" allow="bluetooth"></iframe>Without both permissions, requestDevice() can fail even when the browser and hardware otherwise support Web Bluetooth.
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MDN classifies Web Bluetooth as experimental and not Baseline because it is unavailable in some widely used browsers. Support differs by browser, operating system, device adapter, and enterprise policy. Check the live compatibility table for your exact deployment target instead of promising universal support.
- Serve the page from HTTPS and verify
window.isSecureContext. - Test in the browser and operating system your users actually run.
- Use a real BLE peripheral advertising the required service.
- Trigger
requestDevice()directly from a visible user action. - Document the service and characteristic UUIDs, permissions, payload format, and notification behavior.
- Provide a non-Bluetooth fallback when your application must work in unsupported browsers.
Why requestDevice() fails: troubleshooting
“Web Bluetooth is unavailable”
The browser may not implement the API, the page may not be secure, or an embedded context may be blocked. Check navigator.bluetooth, load the page over HTTPS, and verify the target browser’s current compatibility data.
“User activation is required”
The call was detached from a user gesture. Move requestDevice() into the click or tap handler; do not await unrelated work before invoking it.
The chooser is empty
Your filters may not match what the peripheral advertises, the device may not be discoverable, or the adapter may be off. Confirm the advertised service UUID and temporarily use a narrow name-plus-service filter rather than broad assumptions. acceptAllDevices can help diagnose discovery, but still requires optionalServices for later access.
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“Origin is not allowed” or a policy error
Check the top-level response’s Permissions Policy and, for an iframe, add allow="bluetooth" and authorize the iframe origin. A cross-origin frame cannot grant itself permission.
“Service not found” or “Characteristic not found”
The UUID is wrong, the firmware does not expose that service, or the service was not authorized in filters or optionalServices. Inspect the peripheral’s GATT definition and reacquire objects after reconnecting.
The device disconnects during a read or write
Radio range, power management, peripheral firmware, and concurrent connections can interrupt GATT. Listen for gattserverdisconnected, show a recoverable status, reconnect, and repeat service discovery rather than reusing stale characteristic objects.
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Frequently Asked Questions
Can Web Bluetooth connect to classic Bluetooth devices?
No. The Web Bluetooth API is designed for Bluetooth Low Energy peripherals that expose GATT services and characteristics; a classic Bluetooth profile is not automatically accessible through this API.
Can a page reconnect to a previously authorized device without showing the chooser?
A page can work with a previously obtained device object in supported implementations, but connection can still fail because of adapter state, range, permissions, or device availability. Build explicit reconnect and error handling rather than assuming persistence.
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Should I use a service UUID or acceptAllDevices?
Prefer a service-based filter when you know the required service. It narrows discovery and documents the capability you need. Use acceptAllDevices only when you cannot identify a service ahead of time, and authorize access with optionalServices.
Quick Recap
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