Free Modbus Poll Alternatives in 2026
Modbus Poll is the long-standing Windows tool for acting as a Modbus master, and it is commercial software with a trial. If you need to read an inverter, meter or PLC today without buying a license, or you’re on macOS or Linux, there are good free options. They differ mainly in platform, in how well they decode data types and byte order, and in whether you also need other protocols.
Details reflect the projects as of September 2026. Check each project’s page for current versions and licensing.
Quick comparison
| Tool | Type | Platforms | Modbus transports | Beyond Modbus |
|---|---|---|---|---|
| Ranaliz iOT Tester | Desktop app, open source (MIT) | Windows, macOS (Apple Silicon) | TCP, UDP, RTU | IEC-104 client + RTU simulator, MQTT, Zigbee |
| QModMaster | Desktop app, open source | Windows (Qt; other platforms by building from source) | TCP, RTU | — |
| CAS Modbus Scanner | Desktop utility, free | Windows | TCP, RTU | — |
| Radzio! Modbus Master Simulator | Desktop utility, free | Windows | TCP, RTU | — |
| mbpoll | Command line, open source | Linux (incl. Raspberry Pi), others from source | TCP, RTU | — |
| pymodbus | Python library, open source | Anywhere Python runs | TCP, UDP, RTU, ASCII | Build your own |
| Node-RED + Modbus nodes | Flow-based, open source | Anywhere Node.js runs | TCP, RTU | Everything Node-RED connects to |
What to look for in a Modbus master tool
- Function code coverage. At least FC03/FC04 for reads and FC06/FC16 for writes. Some devices accept only FC16 for writes.
- Data type and byte-order decoding. 32-bit floats and integers span two registers, and devices disagree about word order. A tool that shows the same registers as int, uint, float and hex in several byte orders saves the most time.
- Visible exception codes. You want to see “exception 02”, not just “error”. See Modbus exception codes.
- Serial settings. Baud, parity and stop bits for RTU, plus a sane timeout.
- History and export. When you hand results to a colleague or a vendor, a CSV beats screenshots.
The tools
Ranaliz iOT Tester
A free desktop app from Ranaliz covering Modbus TCP, UDP and RTU with FC01–FC16. It shows live tables, keeps a transaction history, decodes int/uint/float/hex/binary/ASCII with selectable endianness, and exports to Excel/CSV. The same window adds an IEC 60870-5-104 client and RTU simulator, an MQTT test client and a Zigbee tab. That’s useful when a plant mixes Modbus inverters with an IEC-104 grid connection. The source is on GitHub under MIT.
Best for: commissioning engineers who switch between Modbus, IEC-104 and MQTT, and macOS users. → Download iOT Tester
Limits: Windows x64 and Apple Silicon builds are provided. Intel Macs need a local build. It’s a test tool, not a data logger.
QModMaster
An open-source Qt-based Modbus master for TCP and RTU, with a bus monitor that shows raw frames.
Best for: Windows users who want a free, no-frills master and like seeing raw traffic. Limits: Development has been slow for years, and data-type decoding is basic.
CAS Modbus Scanner
A free Windows utility from Chipkin for scanning and reading Modbus TCP and RTU devices.
Best for: quickly scanning a range of addresses or slave IDs to see what answers. Limits: Windows only, and aimed at reading rather than full write workflows.
Radzio! Modbus Master Simulator
A small free Windows master tool that supports TCP and RTU with multiple register windows.
Best for: lightweight read/write checks on Windows laptops. Limits: Windows only, and a dated interface.
mbpoll
An open-source command-line Modbus master, popular on Linux and Raspberry Pi.
Best for: scripting, SSH sessions into field gateways, and headless boxes. Limits: Command line only. Decoding complex data types is up to you.
pymodbus
The widely used Python Modbus library, with client and server implementations.
Best for: developers who want to automate tests or build a custom collector. Limits: You write the tool yourself.
Node-RED with Modbus nodes
Community Modbus nodes let Node-RED flows read and write Modbus devices and pass data on to dashboards, MQTT or databases.
Best for: quick prototypes that need to move data somewhere after reading it. Limits: Heavier setup than a single-purpose tester.
Which one should you use?
| Situation | Pick |
|---|---|
| One-off check on Windows, Modbus only | QModMaster or Radzio |
| You’re on macOS | Ranaliz iOT Tester |
| Modbus plus IEC-104 or MQTT on the same job | Ranaliz iOT Tester |
| Headless Linux gateway over SSH | mbpoll |
| Automated regression tests | pymodbus |
| Read, then forward to a dashboard | Node-RED |
Reading a solar inverter?
Many inverters follow the SunSpec layout, so the same steps work across brands. SunSpec Modbus: how to read solar inverter data walks through finding the map and decoding scale factors.
FAQ
Is there a free version of Modbus Poll?
Modbus Poll offers a time-limited trial. For permanent free use, pick one of the tools above.
Which free Modbus tool works on macOS?
Ranaliz iOT Tester ships a native Apple Silicon build. pymodbus and Node-RED also run on macOS if you’re comfortable with code or flows.
What’s the difference between a Modbus master and a slave simulator?
A master (client) sends requests to real devices, which is what Modbus Poll does. A slave (server) simulator pretends to be a device, so you can test a master or SCADA without hardware.
Sources
- Project pages and repositories of each tool listed (QModMaster, mbpoll, pymodbus, Node-RED Modbus nodes, Chipkin CAS Modbus Scanner, Radzio Modbus Master Simulator, Witte Software Modbus Poll)
- Ranaliz iOT Tester repository: github.com/Ranaliz/ranaliz-iot-tester
