PLCcom.Mqtt.Client 2.1.2

PLCcom.Mqtt.Client

A modern, easy-to-use MQTT client for .NET — supporting both MQTT 3.1.1 and MQTT 5.0. Connect, publish, subscribe and receive with just a few lines of code, without having to learn the MQTT wire protocol first.

Runs on .NET Framework 4.7.2+, .NET Standard 2.1, .NET 8, .NET 9 and .NET 10.

What you get

• A comfortable high-level client — connect, subscribe, publish and receive with a fluent builder
• MQTT 3.1.1 and MQTT 5.0 — choose the protocol per connection, or let the client auto-negotiate
• All three Quality-of-Service levels — QoS 0 (at most once), 1 (at least once), 2 (exactly once)
• Automatic keep-alive, sessions and reconnect, plus Last-Will support
• TLS (mqtts://) and WebSocket (ws://, wss://) transports
• MQTT 5 features — retained messages, topic aliases, shared subscriptions, request/response, enhanced authentication
• Built-in diagnostics through a single listener interface

Getting started

1. Install the package

Install-Package PLCcom.Mqtt.Client

2. A license is required

Every client needs your PLCcom license (user name + serial). Without a valid key the software may be used for test purposes for a limited time — see the included EULA for details. The license is supplied once, on the builder (.WithLicense(...)).

3. Connect, subscribe, publish and receive — C#

using PLCcom.Mqtt.Client;

// Build the client — the license is set once, here on the builder.
PlccomMqttClient client = new PlccomMqttClientBuilder()
    .WithLicense("<Your UserName>", "<Your Serial>")
    .WithIdentifier("my-first-client")
    .WithEndpoint("mqtt://localhost:1883")   // mqtt:// mqtts:// ws:// wss://
    .UseMqtt311()                            // or .UseMqtt5() / .UseAutoProtocol()
    .WithKeepAliveSeconds(30)
    .Build();

client.Connect();

// Subscribe — a Topic Filter may use the wildcards + (one level) and # (the rest).
client.CreateSubscribeBuilder("plccom/demo/#").WithQos1().Send();

// Publish — a Topic Name is exact and has no wildcards.
client.CreatePublishBuilder("plccom/demo/hello", "Hello MQTT").WithQos1().Send();

// Receive the next message (waits up to 3000 ms).
PlccomMqttMessage message = client.Receive(3000);
Console.WriteLine($"{message.TopicName} = {message.GetPayloadText()}");

client.Dispose();

The same in Visual Basic

Imports PLCcom.Mqtt.Client

' Build the client — the license is set once, here on the builder.
Dim client As PlccomMqttClient = New PlccomMqttClientBuilder().
    WithLicense("<Your UserName>", "<Your Serial>").
    WithIdentifier("my-first-client").
    WithEndpoint("mqtt://localhost:1883").
    UseMqtt311().
    WithKeepAliveSeconds(30).
    Build()

client.Connect()

client.CreateSubscribeBuilder("plccom/demo/#").WithQos1().Send()
client.CreatePublishBuilder("plccom/demo/hello", "Hello MQTT").WithQos1().Send()

Dim message As PlccomMqttMessage = client.Receive(3000)
Console.WriteLine(message.TopicName & " = " & message.GetPayloadText())

client.Dispose()

Every high-level call returns a result object (PlccomMqttConnectResult, PlccomMqttSubscribeResult, PlccomMqttPublishResult, …) that carries an IsGood flag together with Quality and Message, so you can check success explicitly:

PlccomMqttConnectResult result = client.Connect();
if (!result.IsGood)
    Console.WriteLine($"CONNECT failed: {result.Quality} - {result.Message}");

Need a broker too?

Add PLCcom.Mqtt.Broker to host your own MQTT broker — embedded in the same application or standalone. Client and broker share the same diagnostics and result types.

System requirements

• Microsoft .NET Framework 4.7.2 or higher (up to 4.8.1)
• Microsoft .NET 5.0 to 7.0 via .NET Standard 2.1
• Microsoft .NET 8.0, .NET 9.0 and .NET 10.0

To build and run the included examples: Visual Studio 2022 or higher.

Examples & documentation

• Ready-to-run C# and Visual Basic workshops: https://github.com/indi-an-gmbh/PLCcom-mqtt-example-dotnet
• Product overview: https://www.indi-an.com/en/plccom/mqtt/
• Questions or feedback: support@indi-an.com

© Indi.An GmbH. Use of this software is subject to the End User License Agreement included in this package (EULA_PLCcom_MQTT_en_06-2026.txt).