PLCcom MQTT SDK for .NET (C#, VB.NET) and Java

PLCcom for MQTT is a professionally maintained MQTT SDK — a native client and broker library for .NET (C#, VB.NET) and Java, for direct integration of MQTT communication into your own applications.
Depending on the product variant, applications can operate as an MQTT client, as an embedded MQTT broker, or in both roles.

The SDK supports MQTT 3.1.1 and MQTT 5.0 over TCP, TLS, WebSocket, and Secure WebSocket. The protocol version can be selected manually or automatically. Publish and Subscribe, QoS 0, 1, and 2, Retained Messages, Last Will, and a wide range of MQTT 5 features are available through a clearly structured API.

The broker is integrated directly into your own application. No separate broker service or connection to a cloud or SaaS solution is required.

PLCcom for MQTT is available as a client SDK, a broker SDK, or a combined client and broker solution. Both components are integrated directly into your own .NET or Java application.

The client allows applications to publish messages, subscribe to topics, and communicate with existing MQTT brokers. The broker accepts MQTT connections, manages sessions and subscriptions, and distributes messages to connected clients.

The broker runs inside your own application. Configuration, lifecycle, authentication, and data processing remain under the control of your software. No separate broker service or cloud or SaaS platform is required.

Depending on the selected version, PLCcom for MQTT is provided as .NET assemblies or as 100% Java libraries. The components are integrated directly into your own project — for .NET through NuGet or by referencing the assemblies, and for Java through Maven Central or as Java libraries.

The MQTT implementation is written entirely in .NET or Java. No C or C++ components are accessed through wrappers. Developers work directly with the SDK’s classes, data types, and functions in their target environment.

PLCcom for MQTT can be used in both 32-bit and 64-bit environments and supports cross-platform applications.

Several MQTT client instances, broker instances, and broker listeners can run within the same application. Combined client and broker scenarios are also possible.

Both components can be used separately or together and can be configured to match the requirements of the application.

PLCcom for MQTT supports encrypted connections over TLS and Secure WebSocket. Both the client and the broker can use server and client certificates, Mutual TLS, and authentication with a username and password.

For more advanced use cases, MQTT 5 Enhanced Authentication, custom connection checks, and topic-based authorization in the broker are available. This allows the security logic to be integrated into the user and permission management of your own application.

PLCcom for MQTT is available as a .NET version and a Java version.

• .NET version: Supports .NET Framework 4.7.2/4.8, .NET Standard 2.1, .NET 8, .NET 9, and .NET 10. Depending on the required functionality, integration is provided through the NuGet packages PLCcom.Mqtt.Client, PLCcom.Mqtt.Broker or through the official Indi.An download. The shared package PLCcom.Mqtt.Core is added automatically as a dependency.
• Java version: Supports Java 11 and has been tested up to Java 26. Depending on the required functionality, integration is provided through the Maven Central artifacts com.indi-an.plccom:plccom-mqtt-client, com.indi-an.plccom:plccom-mqtt-broker or through the official Indi.An download. The shared artifact com.indi-an.plccom:plccom-mqtt-core is added automatically as a dependency.

PLCcom for MQTT is available as a client license, broker license or a combined client and broker license. Customers can choose between an individual developer license for freelancers and a company license covering all developers within the company.

No additional runtime license fees apply to applications created and distributed with the SDK. The number of installations or distributed applications does not result in any further license fees.

Transparent pricing and a 14-day trial version are available for planning purposes. A maintenance plan with a minimum term of one year is included with every licence purchase.

Support is provided directly by the manufacturer for technical questions about integration, licensing, and the use of the client and broker in your own applications.

A wide range of free libraries and broker solutions is available for MQTT. However, for commercially distributed software products, the technical feature set of a component is often not enough. Manufacturers must also consider maintenance, vulnerability management, documentation, and long-term availability.

PLCcom for MQTT is provided as a professionally maintained software component. This includes direct support from the manufacturer, a maintenance plan, traceable releases, and CRA-related documentation for integration into your own software products.

The SDK is therefore aimed especially at software manufacturers and developers who need a responsible contact and predictable product maintenance for the components they use.

An EU Declaration of Conformity, a Simplified EU Declaration of Conformity, and a Security & Integration Guide are available for PLCcom for MQTT for both .NET and Java.

The release documentation also includes a Software Bill of Materials (SBOM) and the results of the vulnerability scan. This provides manufacturers with the information they need to assess and document the component within their own product.

PLCcom for MQTT is used in QuickHMI both as an MQTT client and as an embedded MQTT broker. The components are therefore not only available as a standalone SDK, but are also used in our own professional software product.

Experience from integration, maintenance, and support flows directly into the ongoing development and improvement of PLCcom for MQTT.

For connection tests, commissioning, and troubleshooting, we provide two free standalone test apps. Both applications are based on PLCcom for MQTT.

With the MQTT Client Tool , you can connect to MQTT brokers, publish messages, and subscribe to topics. The MQTT Broker Tool provides a ready-to-use MQTT broker for testing external clients and typical communication workflows.

You can find the test apps in the Downloads section.