Connect Node.js to an MQTT broker with MQTT.js. Start on the free public broker, then point the same code at a secure private broker on ConnectMQ.
mqtt-code-samples/nodejsClone 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 mqtt from "mqtt";
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)
const client = mqtt.connect("mqtt://broker.connectmq.com:1883");
// Runs when the connection is established
client.on("connect", () => {
// Subscribe to the temperature topic
client.subscribe(topic, { qos: 1 });
// Publish a JSON reading
client.publish(topic, JSON.stringify({ temperature: 21.5 }), { qos: 1 });
});
// Runs for every message on a subscribed topic
client.on("message", (t, payload) => console.log(t, payload.toString()));
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 mqtt from "mqtt";
const topic = "your-project/sensors/temperature";
// Connect to your private ConnectMQ broker on port 8883
const client = mqtt.connect("mqtts://YOUR_BROKER_HOST:8883", {
// Username and password from your ConnectMQ dashboard
username: "YOUR_USERNAME",
password: "YOUR_PASSWORD",
});
// Runs when the connection is established
client.on("connect", () => {
// Subscribe to the temperature topic
client.subscribe(topic, { qos: 1 });
// Publish a JSON reading
client.publish(topic, JSON.stringify({ temperature: 21.5 }), { qos: 1 });
});
// Runs for every message on a subscribed topic
client.on("message", (t, payload) => console.log(t, payload.toString()));
Install MQTT.js 5, 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.
