Connect C# and .NET to an MQTT broker with MQTTnet. Start on the free public broker, then point the same code at a secure private broker on ConnectMQ.
mqtt-code-samples/csharpClone 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.
using MQTTnet;
using MQTTnet.Client;
var topic = "your-project/sensors/temperature"; // Use a unique topic prefix: everyone can read the public broker
var client = new MqttFactory().CreateMqttClient();
// Runs for every message on a subscribed topic
client.ApplicationMessageReceivedAsync += e =>
{
Console.WriteLine($"{e.ApplicationMessage.Topic}: {e.ApplicationMessage.ConvertPayloadToString()}");
return Task.CompletedTask;
};
// Connect to the free public broker (no account needed)
var options = new MqttClientOptionsBuilder()
.WithTcpServer("broker.connectmq.com", 1883)
.Build();
await client.ConnectAsync(options);
// Subscribe to the temperature topic
await client.SubscribeAsync(topic);
// Publish a JSON reading
await client.PublishStringAsync(topic, "{\"temperature\":21.5}");
// Keep the client running
Console.ReadLine();
The public broker is shared: anyone can subscribe to your topics. Never send passwords, personal data or anything confidential through it.
About the free public MQTT brokerFor real devices, use a private serverless MQTT broker on ConnectMQ instead of the public one: TLS encryption, a username and password for every device and per-topic access control, fully managed. Start on the Free plan — no card required.
Replace YOUR_BROKER_HOST, YOUR_USERNAME and YOUR_PASSWORD with the values from your ConnectMQ dashboard.
using MQTTnet;
using MQTTnet.Client;
var topic = "your-project/sensors/temperature";
var client = new MqttFactory().CreateMqttClient();
// Runs for every message on a subscribed topic
client.ApplicationMessageReceivedAsync += e =>
{
Console.WriteLine($"{e.ApplicationMessage.Topic}: {e.ApplicationMessage.ConvertPayloadToString()}");
return Task.CompletedTask;
};
// Connect to your private ConnectMQ broker on port 8883
var options = new MqttClientOptionsBuilder()
.WithTcpServer("YOUR_BROKER_HOST", 8883)
// Username and password from your ConnectMQ dashboard
.WithCredentials("YOUR_USERNAME", "YOUR_PASSWORD")
// TLS: the system CA store verifies the broker certificate
.WithTlsOptions(o => o.UseTls())
.Build();
await client.ConnectAsync(options);
// Subscribe to the temperature topic
await client.SubscribeAsync(topic);
// Publish a JSON reading
await client.PublishStringAsync(topic, "{\"temperature\":21.5}");
// Keep the client running
Console.ReadLine();
Install MQTTnet 4, 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 exampleConnect Go to an MQTT broker with the Eclipse Paho Go client.
View examplePublish and subscribe from the command line with mosquitto_pub and mosquitto_sub.
View exampleConnect Java to an MQTT broker with the Eclipse Paho Java client.
View exampleConnect Rust to an MQTT broker with the rumqttc crate.
View exampleConnect Dart and Flutter apps to an MQTT broker with the mqtt_client package.
View exampleConnect native iOS (Swift) and Android (Kotlin) apps to an MQTT broker.
View exampleConnect Home Assistant to an MQTT broker and turn MQTT messages into sensors.
View exampleConnect Node-RED to an MQTT broker with an importable flow.
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.
