Connect Dart and Flutter apps to an MQTT broker with the mqtt_client package. Start on the free public broker, then point the same code at a secure private broker on ConnectMQ.
mqtt-code-samples/dart-flutterClone the complete, runnable examples. Stars and pull requests welcome. View on GitHub No account needed: connect to broker.connectmq.com on port 1883 and start publishing in seconds.
import 'dart:convert';
import 'package:mqtt_client/mqtt_client.dart';
import 'package:mqtt_client/mqtt_server_client.dart';
Future<void> main() async {
const topic = 'your-project/sensors/temperature'; // Use a unique topic prefix: everyone can read the public broker
// Connect to the free public broker (no account needed) (Every client needs a unique client ID)
final client = MqttServerClient.withPort('broker.connectmq.com', 'flutter-example', 1883);
client.keepAlivePeriod = 30;
await client.connect();
// Subscribe to the temperature topic
client.subscribe(topic, MqttQos.atLeastOnce);
// Runs for every message on a subscribed topic
client.updates!.listen((messages) {
final message = messages.first.payload as MqttPublishMessage;
final text = MqttPublishPayload.bytesToStringAsString(message.payload.message);
print('${messages.first.topic}: $text');
});
// Publish a JSON reading
final builder = MqttClientPayloadBuilder()..addString(jsonEncode({'temperature': 21.5}));
client.publishMessage(topic, MqttQos.atLeastOnce, builder.payload!);
}
The public broker is shared: anyone can subscribe to your topics. Never send passwords, personal data or anything confidential through it.
About the free public MQTT brokerFor real devices, use a private serverless MQTT broker on ConnectMQ instead of the public one: TLS encryption, a username and password for every device and per-topic access control, fully managed. Start on the Free plan — no card required.
Replace YOUR_BROKER_HOST, YOUR_USERNAME and YOUR_PASSWORD with the values from your ConnectMQ dashboard.
import 'dart:convert';
import 'package:mqtt_client/mqtt_client.dart';
import 'package:mqtt_client/mqtt_server_client.dart';
Future<void> main() async {
const topic = 'your-project/sensors/temperature';
// Connect to your private ConnectMQ broker on port 8883 (Every client needs a unique client ID)
final client = MqttServerClient.withPort('YOUR_BROKER_HOST', 'flutter-example', 8883);
client.keepAlivePeriod = 30;
// TLS: the system CA store verifies the broker certificate
client.secure = true;
// Username and password from your ConnectMQ dashboard
await client.connect('YOUR_USERNAME', 'YOUR_PASSWORD');
// Subscribe to the temperature topic
client.subscribe(topic, MqttQos.atLeastOnce);
// Runs for every message on a subscribed topic
client.updates!.listen((messages) {
final message = messages.first.payload as MqttPublishMessage;
final text = MqttPublishPayload.bytesToStringAsString(message.payload.message);
print('${messages.first.topic}: $text');
});
// Publish a JSON reading
final builder = MqttClientPayloadBuilder()..addString(jsonEncode({'temperature': 21.5}));
client.publishMessage(topic, MqttQos.atLeastOnce, builder.payload!);
}
Install mqtt_client, connect to the broker host on port 1883 (or 8883 with TLS), then subscribe to a topic and publish messages to it. The examples on this page connect to the free public broker broker.connectmq.com and to a private ConnectMQ broker.
Yes. broker.connectmq.com is a free public MQTT broker that needs no account. Anyone can read its topics, so use it only for tests and use a unique topic prefix.
Connect over TLS on port 8883 with a username and password from your ConnectMQ dashboard, and give every device its own credentials and topic permissions instead of using the public broker.
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View exampleTest any example on broker.connectmq.com — no sign-up, MQTT 3.1.1 and 5, TCP, TLS and WebSocket.
About the free public MQTT brokerWhen it is time for real devices, run the same code on a private, fully managed ConnectMQ broker with TLS and per-device credentials.
Start for freeCreate an account, get your broker credentials and connect your first device — no servers to install, patch or scale.
