Modbus testing tools compared: Modbus Poll, mbpoll, QModMaster, apps
· By Vladimir Chemeris, developer of Modbus TCP FieldKit
Short answer: on a Windows bench, Modbus Poll is the long-established commercial option. For free options, use QModMaster for a GUI and mbpoll for scripts and SSH sessions. pymodbus suits automated tests. A phone app covers site visits where you don’t want to open a laptop. We develop FieldKit, one of the apps listed, so weigh our view with that in mind.
Desktop and command line
| Tool | Runs on | Protocols | Licence | Good for |
|---|---|---|---|---|
| Modbus Poll | Windows | RTU, ASCII, TCP/IP, UDP/IP | Commercial | Daily bench work, Excel link |
| QModMaster | Windows, Linux | RTU, TCP | Free, open source | A free GUI with a bus monitor |
| mbpoll | Linux, Windows, macOS | RTU, TCP | GPL-3.0 | Scripts, SSH, Raspberry Pi |
| pymodbus | Anywhere Python runs | RTU, ASCII, TCP, TLS, UDP | BSD-3-Clause | Automated tests, a simulator |
These details come from each project’s own page on 30 October 2026. Check the price on the vendor’s site.
Watch mbpoll’s default. It starts at reference 1 and sends the address minus one, so mbpoll -r 1 reads protocol address 0. Pass -0 to send protocol addresses as they are. To read two holding registers over TCP on the default port:
mbpoll -t 4 -r 1 -c 2 192.168.1.10iPhone and iPad apps
We read these from the App Store on 30 October 2026 for the US storefront. Prices and features change, and none of them had a rating count there yet.
| App | Price | What its listing covers |
|---|---|---|
| Modbus TCP FieldKit (ours) | $5.99 | Client, foreground server, RTU over TCP, device and Unit ID scan, charts, CSV |
| Modbus TCP Pro | $11.99 | Reads and writes registers, for installers and HVAC technicians |
| Modbus TCP Station | Free download | Modbus TCP master |
| Modbus Connect | Free download | HMI-style dashboard with widgets |
| TCP ModBus | Free download | Client or server, last updated 2016 |
How to choose
You work at a desk, on Windows, all day. Modbus Poll is a long-established commercial tool, with a companion simulator in Modbus Slave.
You need a quick check from a shell. Use mbpoll. It’s easy to script and to run on a Raspberry Pi next to the device.
You’re writing software against Modbus. pymodbus gives you a client and a simulator in one library for your test suite. Then test against real hardware, because simulators differ from devices.
You stand in front of a device, with a phone. Use an app. Check first whether you need a server mode, RTU over TCP and safe writes, since the apps differ on all three.
Our app’s limits
FieldKit has no direct serial or USB connection, no Modbus ASCII, no background operation, and it isn’t available on Mac or Android. There’s no free tier. If you need a free read-only check, one of the free apps or mbpoll may be all you need.
Sources
- Project and vendor pages linked above, 30 October 2026
- App Store listings for the US storefront, 30 October 2026
FAQ
What is a free alternative to Modbus Poll?
QModMaster is a free GUI for Windows and Linux. mbpoll is a free GPL command-line tool for Linux, Windows and macOS. Both support Modbus TCP and RTU.
Is there a Modbus app for iPhone?
Yes, several. Modbus TCP FieldKit, Modbus TCP Pro, Modbus TCP Station, Modbus Connect and TCP ModBus are on the App Store. They differ in price, server support and whether they handle RTU over TCP.
Can an iPhone connect to RS-485 on its own?
Not with these apps. You need a Wi-Fi or Ethernet converter between the phone and the RS-485 line.
Modbus Poll and Modbus Slave are products of Witte Software. Other product names are trademarks of their respective owners.