PLCcom.Mqtt.Broker 2.2.1

PLCcom.Mqtt.Broker

A modern, easy-to-use MQTT broker for .NET — supporting both MQTT 3.1.1 and MQTT 5.0. Host your own broker embedded in an application or as a standalone service, with just a few lines of code.

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

What you get

• A full MQTT broker you can embed in your own .NET application
• MQTT 3.1.1 and MQTT 5.0 clients on the same broker
• Multiple listeners — plain TCP, TLS, WebSocket and secure WebSocket, side by side
• Access control — pluggable authentication and per-topic authorization
• Sessions, retained messages, Last-Will, shared subscriptions
• Custom persistence through a store interface (retained messages / sessions)
• Built-in diagnostics through a single listener interface

Getting started

1. Install the package

Install-Package PLCcom.Mqtt.Broker

2. A license is required

Every broker 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. Start a broker — C#

using PLCcom.Mqtt.Broker;

// Build and start the broker — the license is set once, here on the builder.
PlccomMqttBroker broker = new PlccomMqttBrokerBuilder()
    .WithLicense("<Your UserName>", "<Your Serial>")
    .WithTcpListener("127.0.0.1", 1883)   // add more with AddTlsListener / AddWebSocketListener
    .Start();

// The broker reports the port it actually bound to.
Console.WriteLine($"Broker listening on mqtt://127.0.0.1:{broker.BoundListeners[0].Port}");

// ... broker is now accepting connections ...

broker.Stop();

The same in Visual Basic

Imports PLCcom.Mqtt.Broker

' Build and start the broker — the license is set once, here on the builder.
Dim broker As PlccomMqttBroker = New PlccomMqttBrokerBuilder().
    WithLicense("<Your UserName>", "<Your Serial>").
    WithTcpListener("127.0.0.1", 1883).
    Start()

Console.WriteLine("Broker listening on mqtt://127.0.0.1:" & broker.BoundListeners(0).Port.ToString())

' ... broker is now accepting connections ...

broker.Stop()

With no access validator configured, the broker uses a default open policy (anonymous clients allowed) — convenient for local tests. For production, supply an access validator via .WithAccessValidator(...) to authenticate clients and authorize topic access.

More listeners at once

PlccomMqttBroker broker = new PlccomMqttBrokerBuilder()
    .WithLicense("<Your UserName>", "<Your Serial>")
    .AddTcpListener("0.0.0.0", 1883)
    .AddWebSocketListener("0.0.0.0", 8080)
    .WithMaxConnections(1000)
    .Start();

Need a client too?

Add PLCcom.Mqtt.Client for a matching high-level MQTT client. Client and broker share the same diagnostics and result types, so they pair naturally.

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).