A cross-platform (Windows + macOS) Modbus TCP/RTU master tool — a Qt6/QML clone of Modbus Poll, built with C++20 and CMake.

Two full visual themes ship with the app — Glass HUD and Signal Console — switchable live from a picker on every screen, no restart required.

Point it at a contiguous block of registers and watch them update in place as they poll — no manual re-reads, no guessing whether a value is current. Every field shows exactly what it needs to and nothing more: address, live value, a one-click format editor. Switch addressing convention (0-based PDU or Modicon 4xxxx) or register type mid-session without losing your place.

Most sessions don't need every register in a device — they need the five that actually matter. Favorites lets you hand-pick registers (ad hoc by address, or straight from an imported tag database) into one focused, always-current list, independent of whatever range Normal mode happens to be reading. Writes confirm immediately — the status line above shows exactly what was written and where.

The same curated list, laid out as stat cards with a rolling sparkline per value — built for watching a handful of registers trend over time at a glance, not just reading a single instantaneous number. One toggle switches between List and Cards; nothing about your Favorites selection changes underneath it.

"Import Tags..." loads a CSV or JSON register map — real labels and descriptions ("Ambient Temp," not "register 40021") instead of bare addresses, ready to drop into Favorites via "Add From Tag..." Combined with live search/filter across label, description, address, and unit, a large register map stays navigable instead of turning into a wall of numbers.

That combination — one tool for a full contiguous sweep and a focused live watch list, both addressable by name instead of memorized offsets, in a theme you'd actually want to stare at during a long debugging session — is the whole premise: industrial-tool capability without the industrial-tool interface.

• Modbus TCP and RTU (serial) master, with a connection screen for both transport types (host/port for TCP; port/baud/data bits/parity/stop bits for RTU).
• Live polling of a contiguous register range (Normal view) or a hand-picked list of registers (Favorites view) — exactly one poll loop active at a time, retargeted live when you switch modes.
• Read coalescing: nearby targets are merged into the fewest possible read requests rather than one request per register.
• Register writes (function code 06) with immediate re-read to confirm.
• Value formatting per register: Signed/Unsigned Decimal, Hex, Binary, Float32, Int32 (Signed/Unsigned), with configurable byte order, scale, offset, and unit — editable per-row from a format picker.
• Addressing convention toggle: 0-based (PDU) or Modicon (4xxxx) style addresses, applied consistently across every address field.
• Tag database import from CSV or JSON, driving the Favorites picker and giving registers real labels/descriptions instead of bare addresses.
• Search/filter across label, description, address, and unit, live across both Normal and Favorites views.
• Communication log panel showing raw Tx/Rx frames and errors.
• Auto-reconnect with a "connection lost" state that keeps last-known values on screen (visually marked stale) rather than clearing them.
• Error/stale-value indication per cell when a poll target starts failing.

• Qt 6.5 or newer (developed against 6.11.1)
• CMake 3.21+
• A C++20 compiler — developed with Qt's bundled MinGW 13.1.0 on Windows; any C++20-capable compiler with the required Qt modules should work
• Qt modules: Core Gui Qml Quick QuickControls2 QuickDialogs2 Network SerialPort Test

cmake -S . -B build -DCMAKE_PREFIX_PATH="/path/to/Qt/6.11.1/<kit>" -DCMAKE_BUILD_TYPE=Debug
cmake --build build

On Windows with Qt's bundled MinGW kit:

$env:Path = "C:\Qt\Tools\mingw1310_64\bin;C:\Qt\Tools\Ninja;C:\Qt\6.11.1\mingw_64\bin;" + $env:Path
cmake -S . -B build -G Ninja -DCMAKE_PREFIX_PATH="C:/Qt/6.11.1/mingw_64" -DCMAKE_BUILD_TYPE=Debug
cmake --build build

The executable lands at build/ModbusViewer.exe (or build/ModbusViewer on macOS/Linux). To run it, only the Qt runtime libraries need to be on the loader path — not the full build toolchain.

cd build
ctest --output-on-failure

Tests are Qt Test-based and use a FakeTransport test double for protocol-layer coverage (no real socket/serial I/O needed), plus a real loopback QTcpServer for TCP connection-lifecycle coverage. RTU end-to-end coverage is similarly FakeTransport-based; the one thing that can't be faked is a real serial link, which this project has not yet been tested against.

tools/pymodbus_simulator.py is a Modbus TCP/RTU slave simulator for exercising the app without real hardware, pinned to pymodbus==3.7.4 (see tools/requirements.txt).

pip install -r tools/requirements.txt
python tools/pymodbus_simulator.py --mode tcp --port 502

v1 milestones (M1 through M8 — protocol codec, TCP/RTU transports, polling engine with read coalescing and auto-reconnect, value formatting, tag database, Favorites, search, communication log, and packaging) are complete. See PROGRESS.md for exactly where things stand and docs/roadmap.md for what's planned post-v1. Architecture and design-decision rationale live in docs/, organized by topic (architecture.md, protocol.md, performance.md, favorites-search-tags.md, connection-ux.md, coding-standards.md).

See CONTRIBUTING.md.

MIT — see LICENSE.