What is a good free alternative to Modbus Poll?
Updated 18 September 2026
Modbus Poll is a good, mature Modbus master, and if you live at a Windows desk it is worth what it costs. But it is paid, Windows-only, and a master only — simulating a slave is a second product (Modbus Slave) you buy separately. If what you actually want is a free tool, or one you can carry in front of the equipment on a phone, that is the gap Easy Modbus is built for: it finds equipment, reads and writes registers, works out what each value means, and saves the result — for free, on Android, with a Windows version as well.
What people are really asking
“Modbus Poll alternative” is almost always one of three wishes: I don't want to pay for it, I don't have a Windows laptop where the equipment is, or I want it to also decode the value, not just show me a raw register. It is worth being clear which one you have, because the honest answer is different for each.
An honest comparison
| Modbus Poll | Easy Modbus | |
|---|---|---|
| Platform | Windows desktop | Android phone or tablet, plus a Windows version |
| Price | Paid licence, master and slave sold separately | Free; an optional one-time purchase removes ads and unlocks unlimited saved control panels |
| Reads | Yes, mature and fast | Yes — TCP and RTU-over-TCP, function codes 1–4 |
| Writes | Yes | Yes — off by default, confirmed, read back, with a one-tap Put it back |
| Works out data types for you | You set type and word order yourself | Yes — ranks the plausible readings of a raw register and explains each |
| Saves what a register means | Saves a poll definition | Yes — names, scaling and units per register, exported as CSV |
| Simulates a slave for the bench | Separate product (Modbus Slave) | Built-in device emulator in the Windows version |
| Best at | Desk and bench work on Windows, heavy scripting, long soak tests | Fieldwork on a phone, decoding unknown equipment, leaving a documented map behind |
This is not a “Modbus Poll is bad” page. For desk-bound development and bench simulation it is genuinely good. The point is narrower: if you are paying for it only to read a meter from a plant room, or fighting to get a laptop onto a control network, there is a free tool in your pocket that does that part.
Other free tools people compare
If you specifically want a free Windows desktop master, the names that come up
most are QModMaster, modpoll (a command-line
tool), and CAS Modbus Scanner. They read and write fine. What
they mostly do not do is the part that eats your afternoon: telling you that a raw
0x2A3D across two registers is 12.75 as a word-swapped float rather
than nonsense. See why your
Modbus value looks wrong for why that step matters.
Where Easy Modbus fits
Easy Modbus is the tool for the moment you are standing in front of equipment with a phone and a question: what is on this network, what do these registers mean, and can I change this one safely? It sweeps the subnet for Modbus on port 502, reads blocks of registers, offers the sensible interpretations of each with the reasoning, lets you write with guard rails, and — the part the free desktop tools skip — remembers the whole register map so the next person does not start from zero. See how to use Easy Modbus to read a device end to end.