Append HMI Web

Append HMI Web serves HMI applications (.ahmi projects) made with Append HMI Studio to web browsers. Start it on one PC; operators open the link on any computer, tablet or phone on the network, with live PLC data and no software to install on their side.

• From the command line: append-hmi-web project.ahmi starts the project's web server.

  • --port, --view and --local-only set it up.
  • --headless runs it without a window, for a service.

• From the launcher: with no project, a window opens where you:

  1. pick an .ahmi file;
  2. set the port (default 8480) and the browsers' view;
  3. choose whether other computers may connect;
  4. Start web server, or create a desktop shortcut or menu entry that starts it with those settings.

• The link: once the server runs, the launcher shows the link to open, with Copy and Open buttons, the other addresses the PC answers on, and how many browsers are connected.

• View options in the browser: a small button in the top right corner of the page offers:

  • Fit to window: the whole screen, keeping its proportions;
  • Maximize: stretched to fill the window;
  • Original size: 1:1, with scroll bars;
  • Full screen.
  • Each browser remembers its choice; the launcher sets the starting one.

  

• Everything the Studio's Run does:

  • live PLC data through the bundled hmi-comms server (EtherNet/IP ControlLogix/CompactLogix, SLC 5/05 and MicroLogix, Modbus TCP, simulator);
  • alarms with CSV history;
  • retentive tags;
  • users and access levels;
  • recipes (RecipeExport downloads the CSV file; RecipeImport opens the browser's file picker).

• Several projects at once, each on its own port.

Why port 8480? 8080 and 8088 are often taken on plant PCs (other web servers, Ignition), and a port above 1024 needs no administrator rights.

Managing running servers

• One list for the whole PC: the launcher's Running list shows every Append HMI Web server on this computer: its own, and servers started separately (with --headless, or by another launcher shortcut), marked in the background.
• For each server: the application, its file, its port and how many browsers are connected.
• Restart: stops the server and starts it again with the same settings, reading the .ahmi file afresh. Restart after saving changes in Studio; connected browsers reload by themselves.
• Stop: stops the server. A background process exits once its last server stops.
• Closing the launcher: stops its own servers, after asking. Background servers keep running.

How it works: each server is recorded in servers/ in the settings folder, with a random token readable only by your user account. A launcher sends Stop and Restart to the server's control address (/hmi-web/control), which answers only requests from this computer that carry that token.

How browsers share the application

Every browser runs the application for itself, like separate operator panels on one machine:

• Per browser: its own connection to the PLCs, its own login (users and access levels apply per browser) and its own alarm acknowledgements.
• Shared, kept on the server:
  • alarm history: each real change is written once, however many browsers see it or when they open;
  • retentive values;
  • user changes made at run time;
  • saved recipes: a recipe saved in one browser appears in the others within a few seconds.
• Updates: saving a new version of the .ahmi file and refreshing the browser loads it.
• Server restarts: if the server stops, browsers show "Connection lost" and reload by themselves when it's back.

Security

• Who can connect: anyone who can reach the port can operate the HMI, as anyone at a panel could.
  • Use the application's users and access levels (Studio's HMI > Users and the Enable animation) to protect controls.
  • Untick Allow other computers to connect (--local-only) to serve this PC alone.
• Plain HTTP: the server is meant for the plant network. Don't expose it to the internet.
• What it serves: only the files the HMI page needs, never other files on the PC.
  • The WebSocket accepts only the server's own page.
  • The page runs under a strict Content Security Policy.
• Windows Firewall: the Windows installer lets other computers reach Append HMI Web on private and domain networks, never public ones.

Command line

append-hmi-web [options] [project.ahmi]

  --port <n>                 Web server port (default 8480).
  --view <fit|fill|original> How browsers show the screen at first. Default fit.
  --local-only               Only this computer can connect (127.0.0.1).
  --headless                 No window: print the link and serve until stopped
                             (from the launcher's Running list, Ctrl+C or the OS).
  --create-shortcut <where>  Create a shortcut that starts the server with these
                             options, then exit (<where>: desktop or menu).
  --disable-acceleration     Turn off GPU acceleration.
  -h, --help                 Show help.
  -v, --version              Show the version.

• Exit codes: 0 on success, 1 when the project or port can't be used, 2 for a usage error.
• Windows executable: C:\Program Files\Append HMI Web\Append HMI Web.exe.
• Remembered settings: without options, a project starts with the port, view and access it last used.
• Shortcuts: created per user, with the settings in the command:
  • Windows: Desktop\<project> (web).lnk and Start menu > Append HMI Web;
  • Linux: ~/Desktop and ~/.local/share/applications.

Download

Releases are published at github.com/AppendAutomation/AppendHMIWeb/releases:

• Append-HMI-Web-<version>-Setup.exe
  • Windows 10/11 x64, for all users.
  • Silent install: /S. Silent uninstall: "C:\Program Files\Append HMI Web\Uninstall.exe" /S.
• Append-HMI-Web-<version>-x86_64.AppImage: Linux, runs without installing.
• Append-HMI-Web-<version>-amd64.deb: Debian and Ubuntu.

The installers are not code-signed yet, so Windows SmartScreen asks for confirmation on first run.

Settings, logs and project data are kept in:

• %APPDATA%\Append HMI Web on Windows;
• ~/.config/Append HMI Web on Linux.

The log is logs/main.log.

How it works

Append HMI Web reuses Append HMI Studio's run-only renderer, comms server and data stores unchanged, from the studio/ submodule, as Append HMI Desktop does.

• Serving: the server sends the editor web app's runtime files (46 of its 156 MB, gzipped on the way).
• The bridge: before the page's own scripts, it loads a small bridge (src/web/bridge.js) that stands in for Electron's preload. The runtime's requests go to the server over a WebSocket.
• The server's side: it answers those requests as Studio's main process does for a published package, one session per browser.

Building

With Node.js 22.12+ and the .NET 8 SDK:

git clone --recursive https://github.com/AppendAutomation/AppendHMIWeb.git
cd AppendHMIWeb
npm install
npm run build-comms       # the hmi-comms server, into studio/comms/publish/
npm start                 # the launcher; npm start -- --headless path/to/project.ahmi serves one
npm test
npm run dist-win          # Windows installer (on Linux too, no wine)
npm run dist-linux        # AppImage and deb

Path	Contents
src/main/	Main process: command line, launcher, web server (server.js), browser sessions (rpc.js), shortcuts
src/web/bridge.js	The browser side of the bridge
src/launcher/	The launcher window (plain HTML, no editor code)
studio/	Submodule: AppendHMIStudio, with its drawio fork and comms server
scripts/	Build scripts: installers, NSIS download, icons
src/test/	Unit tests (npm test)

License and attribution

Append HMI Web is © 2026 Append Automation and is licensed under the Apache License 2.0 (see LICENSE).

It is built on Append HMI Studio, which is built on the draw.io diagram editor and drawio-desktop by JGraph Ltd, used and modified under the Apache License 2.0. NOTICE lists the third-party works. Append HMI Web is not affiliated with or endorsed by JGraph Ltd; "draw.io" is a trademark of its owner.