Free Modbus, IEC-104 and MQTT Tester

What a Modbus tester is for

Installing one Modbus tester, then a second tool for IEC-104, then a third MQTT client slows field work. Ranaliz iOT Tester puts those three jobs — plus Zigbee — in a single desktop window. It is not a monitoring platform. It verifies the link, the register map, and the command before you commission a device.

It is built for teams searching for a free Modbus tester, IEC-104 tester, and MQTT test client. There is no license key. Windows 10/11 (x64) and Apple Silicon macOS builds are on the download buttons at the top of this page.

Modbus tester: TCP, UDP, and RTU

Modbus is still the default conversation for inverters, meters, and drives. This Modbus tester supports three transports: TCP, UDP, and serial RTU. After you connect, you pick slave, function code, start address, and count. The table fills live, a transaction history is kept, and results export to Excel/CSV.

Function codes cover FC01–FC16. Register display switches between raw values, int/uint/float, hex, binary, and ASCII/UTF-8/UTF-16, with big/little and swapped endianness. Poll interval, timeout, and serial parameters (baud, parity, stop bits) match the device in front of you.

That answers “is the value right, and is the byte order right?” — not only “did a packet leave.” You can read a Modbus TCP neighbour and move to RTU in the same session without closing the app.

Persistent acquisition and cloud forwarding are a different job. Use the Ranaliz Datalogger for that; iOT Tester does not replace it.

IEC-104 tester: client and RTU simulator

IEC 60870-5-104 is how masters talk to RTUs in distribution and energy automation. This IEC-104 tester works in both directions.

Client: connect to an RTU, run a general interrogation (GI), watch live point updates, write commands. Point types come through c104 (M_SP, M_DP, M_ME, C_SC, C_DC, C_SE, and others).

Server: start an RTU simulator to test a master. “How does this master interpret that ASDU?” can be closed in the lab before anyone drives to site.

Most teams looking for an IEC tester actually need two tools: a client that talks to a real RTU, and a simulator that fools a master. Having both in one window shortens the plug-unplug loop.

MQTT tester and Zigbee

MQTT behaves like an MQTT test client: connect to a broker, subscribe, publish. TLS is optional. You see whether the payload arrives and whether the topic name is right, without installing a separate MQTT explorer.

The Zigbee tab covers coordinator / radio–serial workflows. It is searched less often than Modbus or IEC-104; keeping it in the same install still avoids splitting industrial and IoT protocols across two laptops.

Source and release notes are in the GitHub repository (MIT).

Field guides

• Modbus exception codes 01–0B: causes and fixes
• SunSpec Modbus: how to read solar inverter data
• How to test an IEC 60870-5-104 connection
• Free Modbus Poll alternatives compared

Who should download it

It is for field engineers, system integrators, and software teams bringing a protocol up for the first time. Confirming an inverter Modbus map, seeing an RTU GI response, or checking that an MQTT broker forwards a message in minutes is the job.

Continuous energy monitoring, alarms, and work orders are not. That layer is the Ranaliz Energy Monitoring Platform. iOT Tester closes “does the device actually speak?” before you connect the platform.

For a shorter product overview see the iOT Tester blog post. Downloads are a Windows x64 executable and a macOS arm64 archive; Intel Macs need a local build.