Getting Started

Let's start to create an HelloWorld extension for StarUML. Full source codes of HelloWorld extension are available at

Create an extension

First we need to create an extension folder. Open your extensions folder.

  • MacOS: ~/Library/Application Support/StarUML/extensions/user

  • Windows: C:\Users\<user>\AppData\Roaming\StarUML\extensions\user

  • Linux: ~/.config/StarUML/extensions/user

Create a new folder HelloWorld in your extensions folder.

Extension package layout

An extension may have following folder structure:

├─ menus/
├─ keymaps/
├─ toolbox/
├─ stylesheets/
├─ preferences/
├─ main.js
└─ package.json
  • /menus See Menus.

  • /keymaps See Keymaps.

  • /toolbox See Toolbox.

  • /stylesheets Place CSS stylesheet files (.css).

  • /preferences See Preferences.

  • main.js

  • package.json

Create main.js

Create main.js in the new extension folder. main.js is the entry point to be executed when StarUML is started. init() function will be called when the extension is loaded. init() is optional, not mandatory.

function init() {
  // ...

exports.init = init

Application Context

To write an extension with Javascript, you need to use StarUML's open APIs. You can use most of API functions via the application context object app. The app includes objects providing useful APIs for commands, menus, keymaps, preferences, factory, dialogs, etc. For more about app object, see API Reference.


StarUML is developed based on electron platform, so you can also use electron APIs in your extension.

Add a command

A command is an execution unit which can be bound with a menu item as well as a keyboard shortcut. For more about command, see Commands.

In Hello World extension, we will add a command that showing "Hello, World!" message with id helloworld:show-message as bellow:

function handleShowMessage () {
  window.alert('Hello, world!')

function init () {
  app.commands.register('helloworld:show-message', handleShowMessage)

exports.init = init

You can find and execute the command by Command Palette (Ctrl+Shift+P or Cmd+Shift+P).

Add a menu item

We will add a menu item named Hello World under Tools menu. To add a menu item, we need to create a folder /menus and a menu JSON file helloworld.json in the folder.

├─ menus/
│  └─ helloworld.json
└─ main.js

The menu JSON file is as below:

  "menu": [
      "id": "tools",
      "submenu": [
          "label": "Hello World",
          "id": "tool.helloworld",
          "command": "helloworld:show-message"

Add a shortcut

We will also bind a keyboard shortcut Ctrl+W (Cmd+W for MacOS) to the command, so we need to create a folder /keymaps and a keymap JSON file helloworld.json in the folder.

├─ menus/
│ └─ helloworld.json
├─ keymaps/
│ └─ helloworld.json
└─ main.js

The keymap JSON file is as below:

  "cmdctrl-w": "helloworld:show-message"

Now when user selects the menu item or press Ctrl+W (Cmd+W for MacOS), the command helloworld:show-message will be executed to show alert dialog with message "Hello, World!".

Run and Debug

If you finished editing main.js, then just restart StarUML. However, restarting whenever you modified codes is very tedious. So, just reload by pressing Ctrl+R (Cmd+R for MacOS) or selecting Debug > Reload menu item.

It is useful to use DevTools to debug an extension. To open DevTools, select Debug > Show DevTools. You can see all console errors and logs.

Define package.json

If you consider to distribute your extension to other users, you need to create a package.json file containing metadata for the extension.

  "name": "your_id.helloworld",
  "title": "HelloWorld",
  "description": "HelloWorld extension example.",
  "homepage": "",
  "version": "1.0.0",
  "keywords": ["example", "helloworld"],
  "author": {
    "name": "Minkyu Lee",
    "email": "",
    "url": ""
  "license": "MIT",
  "engines": {
    "staruml": ">=3.0.0"

Restart StarUML and then check whether your extension is properly shown in Extension Manager or not. (select Tools > Extension Manager and click Installed tab).

Distribute your extension

To allow other users to install your extension, there are several possible ways:

  1. Distribute as ZIP archive. Zip the extension folder staruml-helloworld as and just unzip the file in other user's the extensions folder explained above.

  2. Distribute via Github URL. Users can install from Github URL. In Extension Manager, click Install from URL and enter the Github URL (e.g. and press Install button.

  3. Distribute via Extensions Registry. If you want to register official extensions registry. Please contact us (

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