name: webui-dev description: Build interactive WebUI apps with compiled-template hydration, template syntax, component patterns, and CLI usage.

WebUI App Development

Use this skill when building or modifying WebUI applications.

Critical rules (memorize these)

1. Every template binding must exist in the server state JSON. The server renders from JSON. Missing keys render empty.
2. HTML, CSS, TypeScript are separate files. No JSX. No CSS-in-JS. No JS in templates.
3. The <template> tag is optional. The build tool auto-injects it. Include it only for root host events (@custom-event on the shadow root).
4. Components inside <for> loops do NOT inherit loop variables. Pass data via attributes.
5. Expressions in bindings: comparisons and logic OK; ternaries NOT. {{count > 0}}, ?active="{{section == 'guide'}}", <if condition="a && b"> all work. Operators: ==, !=, <, >, <=, >=, &&, ||, !. Forbidden: ternary (? :), function calls, mixing && with ||, more than 5 logical operators. See docs/guide/ai.md for full rules.
6. No this.querySelector() for reactive state. Use @observable + template bindings.
7. Decorators: @attr (HTML attribute), @observable (reactive state). Both work in SSR.
8. @attr({ mode: 'boolean' }) for true/false. Present = true, absent = false. Never use string "false".

Quick reference

import { WebUIElement, attr, observable } from '@microsoft/webui-framework';

export class MyComponent extends WebUIElement {
  @attr label = '';
  @attr({ mode: 'boolean' }) disabled = false;
  @observable count = 0;
  @observable items: Item[] = [];
  inputEl!: HTMLInputElement;  // populated by w-ref="inputEl"

  increment(): void { this.count += 1; }
  onKeydown(e: KeyboardEvent): void { if (e.key === 'Enter') this.submit(); }
}
MyComponent.define('my-component');

webui build ./src --out ./dist --plugin=webui
webui serve ./src --state ./data/state.json --plugin=webui --watch

Full reference

The complete guide covering all template syntax, CLI flags, patterns, anti-patterns, routing, and language integrations:

📖 docs/guide/ai.md

Read that file before generating any WebUI code.