Modbus has been the backbone of industrial communication for over 40 years. It runs PLCs, VFDs, energy meters, flow sensors, and temperature controllers in factories, substations, and buildings all over the world. It is simple, reliable, and it works.
The tooling around it, however, has not kept up. Most Modbus software still looks and works like it was built in 2003 — desktop-only, expensive licenses, no cloud access, and zero support for modern workflows like REST APIs, automated testing, or browser-based monitoring.
ModPackQT is the answer to that gap. It is a web-based Modbus Master/Slave platform designed for engineers and technicians who want modern tooling without giving up on the protocol they know and rely on.
What Is ModPackQT?
ModPackQT is a cloud-hosted Modbus platform with a local gateway component. You interact with it through a browser — no software to install for the main interface — while a small Gateway app runs on your local machine or server to handle the actual Modbus TCP and RTU communication.
The architecture looks like this:
Browser (ModPackQT web app)
↕ cloud relay
Gateway app (your local machine / server)
↕ Modbus TCP or RTU
PLC / VFD / Sensor / Meter
The Gateway bridges your devices to the cloud securely. It auto-updates from the cloud and runs on Windows, macOS, and Linux. You never expose your device network directly.
Core Features
Modbus Master — Read and Write Any Device
The Master panel lets you configure connection profiles for any Modbus TCP device on your network. You set the IP, port, unit ID, and start polling registers with one click.
Supported function codes:
FC1 — Read Coils
FC2 — Read Discrete Inputs
FC3 — Read Holding Registers
FC4 — Read Input Registers
FC5 — Write Single Coil
FC6 — Write Single Register
FC15 — Write Multiple Coils
FC16 — Write Multiple Registers
FC8, FC23, FC43/MEI 14 — advanced diagnostics and device identification
Registers can be saved, named, and monitored in real time with live charting. You can set data types (16-bit int, 32-bit float, BCD), scaling factors, and display formats.
Modbus RTU is also supported — directly in the browser via the WebSerial API if your machine has a USB-to-RS485 adapter. No driver installation needed.
Slave Simulator — Become a Modbus Device
This is one of the most useful features for engineers doing integration testing.
The Slave Simulator lets you create a virtual Modbus TCP slave — a real Modbus TCP server on your network that any master can connect to and read registers from. You control exactly what values those registers hold.
Why this matters:
If you are developing a SCADA screen, an HMI, or a Modbus client application, you normally need real hardware available during development. With the ModPackQT Slave Simulator you don't. You create a slave, set its registers to known test values, and point your software at it. No PLC on the desk required.
AI Quick Setup
Configuring a new Modbus device from scratch — figuring out register maps, unit IDs, data types — takes time. ModPackQT includes an AI Quick Setup feature powered by Google Gemini.
You paste or upload a device datasheet, describe what you want to monitor, and the AI creates the connection profile, slave configuration, and test registers automatically. For common devices it gets the register map right on the first try. For custom devices it gives you a solid starting point to adjust.
This is not a chatbot. It produces actual configuration objects inside the platform — slaves, connections, and register groups — ready to use.
Real-Time Charts and Data Visualization
Every register you save can be charted live. Charts update in real time as the Gateway polls. You can overlay multiple registers on the same chart, set time ranges, and export readings to CSV.
The analytics panels extend to bots — Bot Analytics Charts show you execution history, output values over time, and error rates so you can see exactly how your automation logic is performing.
Modbus Protocol Probe
Not sure what is on your network or what registers a device supports? The Probe feature sweeps a range of Modbus addresses and function codes, reporting which ones respond. Results show up in real time with a live progress indicator and can be exported to CSV.
This is useful when you receive a device with incomplete documentation or need to quickly map out what an existing installation is doing.
Who It Is For
Automation engineers who need to read data from PLCs and sensors during commissioning, troubleshooting, or ongoing monitoring — without installing a full SCADA suite.
Test and integration engineers who need a realistic Modbus slave to test SCADA screens, HMIs, and Modbus client software against predictable data.
System integrators who manage multiple sites and want remote access to device data without VPNs or dedicated remote desktop sessions.
IIoT developers building applications on top of Modbus data — the REST API and Node-RED integration give you clean programmatic access.
Hobbyists and prosumers monitoring solar inverters, heat pumps, EV chargers, and energy meters at home. Most of these devices speak Modbus TCP or RTU, and ModPackQT is one of the fastest ways to get data out of them.
Plans
ModPackQT has a free tier that covers the core master read/write functionality. Paid plans unlock the Slave Simulator, higher connection and register limits, and Node-RED slave nodes.
A 30-day free trial of paid features is available — no credit card required to start.
Full plan details at modpackqt.com/pricing.
Getting Started
Sign up at modpackqt.com — free, no card required
Download the Gateway app from Settings → Gateway (Windows, macOS, Linux)
Run the Gateway — it starts a local REST API on port 8502 and connects to the cloud
Add a connection profile — enter the IP and port of your Modbus device
Start reading registers — pick a function code, set the address range, click Read
For the full documentation visit modpackqt.com/resources.
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