git clone https://github.com/umbraco/Umbraco-CMS
cd Umbraco-CMS/src/Umbraco.Web.UI.Client
npm install

my-extension/
├── index.ts           # REQUIRED - exports manifests
└── my-element.ts      # Your element(s)

import './my-element.js';

export const manifests = [
  {
    type: 'dashboard',
    alias: 'My.Dashboard',
    name: 'My Dashboard',
    element: 'my-element',
    meta: { label: 'My Dashboard', pathname: 'my-dashboard' },
    conditions: [{ alias: 'Umb.Condition.SectionAlias', match: 'Umb.Section.Content' }]
  }
];

// my-element.ts
import { LitElement, html, customElement } from '@umbraco-cms/backoffice/external/lit';

@customElement('my-element')
export class MyElement extends LitElement {
  render() {
    return html`<uui-box headline="Hello">It works!</uui-box>`;
  }
}

cd Umbraco-CMS/src/Umbraco.Web.UI.Client
VITE_EXTERNAL_EXTENSION=/full/path/to/my-extension npm run dev:external

cd Umbraco-CMS/src/Umbraco.Web.UI.Client
npm run example
# Select from list of examples

cd Umbraco-CMS/src/Umbraco.Web.UI.Client
VITE_EXTERNAL_EXTENSION=/path/to/your/extension npm run dev:external

// From Umbraco-CMS/src/Umbraco.Web.UI.Client/index.ts
if (import.meta.env.VITE_EXTERNAL_EXTENSION) {
  const js = await import('@external-extension/index.ts');
  if (js) {
    Object.keys(js).forEach((key) => {
      const value = js[key];
      if (Array.isArray(value)) {
        umbExtensionsRegistry.registerMany(value);
      } else if (typeof value === 'object') {
        umbExtensionsRegistry.register(value);
      }
    });
  }
}

git clone https://github.com/umbraco/Umbraco-CMS
cd Umbraco-CMS/src/Umbraco.Web.UI.Client
npm install

my-extension/
├── index.ts              # Exports manifests array (REQUIRED)
├── my-element.ts         # Your element(s)
├── my-context.ts         # Context (if needed)
├── package.json          # Optional - for IDE support and tests
├── tsconfig.json         # Optional - for IDE support
└── README.md             # Documentation

import './my-dashboard.element.js';

export const manifests = [
  {
    type: 'dashboard',
    alias: 'My.Dashboard',
    name: 'My Dashboard',
    element: 'my-dashboard',
    weight: 100,
    meta: {
      label: 'My Dashboard',
      pathname: 'my-dashboard'
    },
    conditions: [
      {
        alias: 'Umb.Condition.SectionAlias',
        match: 'Umb.Section.Content'
      }
    ]
  }
];

{
  "name": "my-extension",
  "type": "module",
  "devDependencies": {
    "@umbraco-cms/backoffice": "^17.0.0",
    "typescript": "~5.8.0"
  }
}

cd /path/to/Umbraco-CMS/src/Umbraco.Web.UI.Client
VITE_EXTERNAL_EXTENSION=/absolute/path/to/my-extension npm run dev:external

// my-dashboard.element.ts
import { LitElement, html, css, customElement } from '@umbraco-cms/backoffice/external/lit';

@customElement('my-dashboard')
export class MyDashboardElement extends LitElement {
  static override styles = css`
    :host {
      display: block;
      padding: var(--uui-size-layout-1);
    }
  `;

  override render() {
    return html`
      <uui-box headline="My Extension">
        <p>Running in the mocked backoffice!</p>
      </uui-box>
    `;
  }
}

declare global {
  interface HTMLElementTagNameMap {
    'my-dashboard': MyDashboardElement;
  }
}

import { html, customElement, state } from '@umbraco-cms/backoffice/external/lit';
import { UmbLitElement } from '@umbraco-cms/backoffice/lit-element';
import { EXAMPLE_MY_CONTEXT } from './my-context.js';

@customElement('example-my-feature-view')
export class ExampleMyFeatureViewElement extends UmbLitElement {
  @state()
  private _value?: string;

  constructor() {
    super();
    this.consumeContext(EXAMPLE_MY_CONTEXT, (context) => {
      this.observe(context.value, (value) => {
        this._value = value;
      });
    });
  }

  override render() {
    return html`
      <uui-box headline="My Feature Example">
        <p>Current value: ${this._value ?? 'Loading...'}</p>
      </uui-box>
    `;
  }
}

export default ExampleMyFeatureViewElement;

declare global {
  interface HTMLElementTagNameMap {
    'example-my-feature-view': ExampleMyFeatureViewElement;
  }
}

import { UmbContextToken } from '@umbraco-cms/backoffice/context-api';
import { UmbContextBase } from '@umbraco-cms/backoffice/class-api';
import { UmbStringState } from '@umbraco-cms/backoffice/observable-api';
import type { UmbControllerHost } from '@umbraco-cms/backoffice/controller-api';

export class ExampleMyContext extends UmbContextBase {
  #value = new UmbStringState('initial');
  readonly value = this.#value.asObservable();

  constructor(host: UmbControllerHost) {
    super(host, EXAMPLE_MY_CONTEXT);
  }

  setValue(value: string) {
    this.#value.setValue(value);
  }

  getValue() {
    return this.#value.getValue();
  }

  public override destroy(): void {
    this.#value.destroy();
    super.destroy();
  }
}

export const EXAMPLE_MY_CONTEXT = new UmbContextToken<ExampleMyContext>(
  'ExampleMyContext'
);

export { ExampleMyContext as api };

npm install --save-dev @open-wc/testing @web/test-runner @web/test-runner-playwright

npm install --save-dev @playwright/test
npx playwright install chromium

cd examples/workspace-feature-toggle
npm install
npm test              # Unit tests
npm run test:e2e      # E2E tests (requires mocked backoffice running)

cd Umbraco-CMS/src/Umbraco.Web.UI.Client
npm run example
# Select from list