Modbus Slave Simulator

UnSlave is a programmable, developer-friendly Modbus slave simulator.

Unslave makes it possible to simulate any number of Modbus slaves without dealing with manual GUI setup.

If you need automate Modbus testing, this tool is for you.

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Demonstrates Unslave UI with Modbus request frames

The Easiest Way to Communicate With Devices

  • Instant Start

    Getting started with Unslave is quicker than with any other simulator, thanks to it's simple configuration API.

  • JSON Configuration

    Using JSON files for configuration makes it possible to automate testing and track configuration changes.


    Alter configuration at runtime programatically by using an HTTP API.

  • Extensive Logging

    UnSlave can display and store everything that happens on the Modbus netowork, making diagnostics easier.

  • Unlimited Slaves

    Use UnSlave to simulate any number of slaves on the same network.

  • Simulate Exceptions

    You can configure any slave to return a Modbus exception code instead of a register value.

  • Portable

    No installation needed. You can run UnSlave on any Windows PC from a USB drive.

  • Serial/RTU + TCP

    Simulate either RTU or TCP slaves. Or run two UnSlave instances to support both.

  • Value for Free

    It doesn't cost you anything to get and use Unslave.

Powerful Configuration and API

Add any number virtual Modbus slaves, registers and even simulate Modbus exceptions by editing a simple JSON file.

Alternatively, you can use the HTTP API provided by Unslave to update configuration at runtime

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Example of Unslave configuration with multiple Modbus RTU slaves

Pricing - It's Free!

  • 999 Slaves
  • 9999 Registers
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