Quick start

# Subscribe to a topic (keeps listening)
mosquitto_sub -h your-broker.mqtt.one -p 1883 \
  -u "YOUR_USERNAME" -P "YOUR_PASSWORD" \
  -t "your/topic" -q 1 -v

# Publish a message from another terminal
mosquitto_pub -h your-broker.mqtt.one -p 1883 \
  -u "YOUR_USERNAME" -P "YOUR_PASSWORD" \
  -t "your/topic" -m "hello from MQTT One" -q 1

# Encrypted connection over TLS
mosquitto_sub -h your-broker.mqtt.one -p 8883 --capath /etc/ssl/certs \
  -u "YOUR_USERNAME" -P "YOUR_PASSWORD" -t "your/topic"

# pip install paho-mqtt
import paho.mqtt.client as mqtt

BROKER = "your-broker.mqtt.one"
TOPIC = "your/topic"

def on_connect(client, userdata, flags, reason_code, properties):
    print("Connected:", reason_code)
    client.subscribe(TOPIC, qos=1)

def on_message(client, userdata, msg):
    print(msg.topic, msg.payload.decode())

client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2)
client.username_pw_set("YOUR_USERNAME", "YOUR_PASSWORD")
client.on_connect = on_connect
client.on_message = on_message

client.connect(BROKER, 1883, keepalive=60)
client.publish(TOPIC, "22.5", qos=1)
client.loop_forever()

// ESP32 / ESP8266 with the PubSubClient library
#include <WiFi.h>          // use <ESP8266WiFi.h> on ESP8266
#include <PubSubClient.h>

const char* WIFI_SSID = "YOUR_WIFI";
const char* WIFI_PASS = "YOUR_WIFI_PASSWORD";
const char* BROKER    = "your-broker.mqtt.one";
const char* MQTT_USER = "YOUR_USERNAME";
const char* MQTT_PASS = "YOUR_PASSWORD";
const char* TOPIC     = "your/topic";

WiFiClient net;
PubSubClient mqtt(net);

void onMessage(char* topic, byte* payload, unsigned int length) {
  Serial.printf("%s: %.*s\n", topic, (int)length, (char*)payload);
}

void reconnect() {
  while (!mqtt.connected()) {
    String id = "esp32-" + String((uint32_t)ESP.getEfuseMac(), HEX);
    if (mqtt.connect(id.c_str(), MQTT_USER, MQTT_PASS)) {
      mqtt.subscribe(TOPIC);
    } else {
      delay(3000);
    }
  }
}

void setup() {
  Serial.begin(115200);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) delay(500);
  mqtt.setServer(BROKER, 1883);
  mqtt.setCallback(onMessage);
}

void loop() {
  if (!mqtt.connected()) reconnect();
  mqtt.loop();

  static unsigned long last = 0;
  if (millis() - last > 10000) {
    last = millis();
    mqtt.publish(TOPIC, String(analogRead(34)).c_str());
  }
}

// npm install mqtt
import mqtt from "mqtt";

const client = mqtt.connect("mqtt://your-broker.mqtt.one:1883", {
  username: "YOUR_USERNAME",
  password: "YOUR_PASSWORD",
  clientId: "node-" + Math.random().toString(16).slice(2, 10),
});

client.on("connect", () => {
  client.subscribe("your/topic", { qos: 1 });
  client.publish("your/topic", JSON.stringify({ temp: 22.5 }), { qos: 1 });
});

client.on("message", (topic, payload) => {
  console.log(topic, payload.toString());
});

<!-- MQTT over secure WebSocket, directly from the browser -->
<script src="https://unpkg.com/mqtt/dist/mqtt.min.js"></script>
<script>
  const client = mqtt.connect("wss://your-broker.mqtt.one:8084/mqtt", {
    username: "YOUR_USERNAME",
    password: "YOUR_PASSWORD",
  });

  client.on("connect", () => client.subscribe("your/topic"));
  client.on("message", (topic, payload) => {
    document.body.insertAdjacentText("beforeend", topic + ": " + payload + "\n");
  });

  // Plain WebSocket is also available: ws://your-broker.mqtt.one:8083/mqtt
</script>