Agent Skills: VS Code Extension

VS Code Extension

Build VS Code extensions from scratch or convert existing web apps into portable, shareable extensions.

Architecture

VS Code extensions run in two contexts:

1. Extension Host (Node.js) — Backend logic, file access, VS Code APIs
2. Webviews (browser sandbox) — Custom UIs with HTML/CSS/JS (React, Vue, vanilla)

Build stack: TypeScript + esbuild (extension) + Vite (webviews)

Quick Start

1. Choose a template from assets/ based on your needs (see decision tree below)
2. Copy the template to your project directory
3. Update package.json: name, displayName, publisher, description
4. Run npm install then npm run build
5. Press F5 in VS Code to launch Extension Development Host

Template Decision Tree

| Need | Template | |------|----------| | Simple command/action | assets/basic-command/ | | Custom UI panel (React) | assets/webview-react/ | | Sidebar file tree | assets/tree-view/ | | Custom file editor | assets/custom-editor/ | | AI agent integration | assets/file-bridge/ |

Extension Types

Commands

Register actions triggered via Command Palette, keyboard shortcuts, or menus.

vscode.commands.registerCommand('myExt.doSomething', () => {
  vscode.window.showInformationMessage('Done!');
});

See references/api-reference.md for common APIs.

Webviews

Full HTML/CSS/JS UIs in panels or sidebar. Use React for complex interfaces.

const panel = vscode.window.createWebviewPanel(
  'myView', 'My Panel', vscode.ViewColumn.One,
  { enableScripts: true }
);
panel.webview.html = getWebviewContent();

See references/webview-patterns.md for React setup, messaging, and CSP.

Tree Views

Hierarchical data in the sidebar (file explorers, outlines, lists).

vscode.window.registerTreeDataProvider('myTreeView', new MyTreeProvider());

See references/tree-view-patterns.md for TreeDataProvider patterns.

Custom Editors

Replace the default editor for specific file types.

vscode.window.registerCustomEditorProvider('myExt.myEditor', new MyEditorProvider());

See references/custom-editor-patterns.md for document sync and undo/redo.

Converting Existing Apps

To convert a JS/React/Vue app into an extension:

1. Assess — What does the app do? What VS Code features does it need?
2. Map APIs — Replace web APIs with VS Code equivalents
3. Restructure — Move UI into webview, logic into extension host
4. Connect — Wire up postMessage communication

| Web API | VS Code Equivalent | |---------|-------------------| | localStorage | context.globalState / context.workspaceState | | fetch() | vscode.workspace.fs or keep fetch for external APIs | | Router | Multiple webview panels or sidebar views | | alert() | vscode.window.showInformationMessage() | | prompt() | vscode.window.showInputBox() | | confirm() | vscode.window.showWarningMessage() with options |

See references/conversion-guide.md for detailed step-by-step process.

Build System

Extension code — Use esbuild (fast, simple):

// esbuild.js
esbuild.build({
  entryPoints: ['src/extension.ts'],
  bundle: true,
  outfile: 'dist/extension.js',
  external: ['vscode'],
  format: 'cjs',
  platform: 'node',
});

Webview code — Use Vite (HMR, React support):

// vite.config.ts
export default defineConfig({
  build: {
    outDir: '../dist/webview',
    rollupOptions: { output: { entryFileNames: '[name].js' } }
  }
});

See references/build-config.md for complete configurations.

package.json Manifest

Essential fields:

{
  "name": "my-extension",
  "displayName": "My Extension",
  "publisher": "your-publisher-id",
  "version": "0.0.1",
  "engines": { "vscode": "^1.85.0" },
  "main": "./dist/extension.js",
  "activationEvents": [],
  "contributes": {
    "commands": [{ "command": "myExt.hello", "title": "Hello" }]
  }
}

The contributes section defines commands, menus, views, settings, keybindings, and more.

See references/contribution-points.md for all contribution types.

IPC Patterns

Extension ↔ Webview

Use postMessage for bidirectional communication:

// Extension → Webview
panel.webview.postMessage({ type: 'update', data: {...} });

// Webview → Extension
panel.webview.onDidReceiveMessage(msg => {
  if (msg.type === 'save') { /* handle */ }
});

Extension ↔ External Tools (AI Agents)

Use file-based IPC for communication with Claude Code or other agents:

// Watch for command files
fs.watch(commandDir, (event, filename) => {
  if (filename.endsWith('.json')) {
    const command = JSON.parse(fs.readFileSync(path.join(commandDir, filename)));
    processCommand(command);
  }
});

See references/ai-integration.md for the file-bridge pattern.

Packaging & Distribution

Package as .vsix

npm install -g @vscode/vsce
vsce package

This creates my-extension-0.0.1.vsix.

.vscodeignore

Exclude unnecessary files:

.vscode/**
node_modules/**
src/**
*.ts
tsconfig.json
esbuild.js
vite.config.ts

Distribution Options

1. Direct sharing — Send .vsix file, install via code --install-extension file.vsix
2. VS Marketplace — Publish with vsce publish (requires Microsoft account)
3. Open VSX — Alternative registry for open-source extensions

Platform-Specific Builds

For extensions with native dependencies:

vsce package --target win32-x64
vsce package --target darwin-arm64
vsce package --target linux-x64

Reference Files

| File | When to Read | |------|--------------| | api-reference.md | Implementing extension features | | contribution-points.md | Configuring package.json contributes | | webview-patterns.md | Building React webviews | | tree-view-patterns.md | Implementing tree views | | custom-editor-patterns.md | Building custom file editors | | build-config.md | Configuring esbuild/Vite | | conversion-guide.md | Converting web apps | | ai-integration.md | Integrating with AI agents |

Asset Templates

| Template | Description | |----------|-------------| | basic-command/ | Minimal extension with one command | | webview-react/ | React webview panel with messaging | | tree-view/ | Sidebar tree view with provider | | custom-editor/ | Custom editor for specific file types | | file-bridge/ | File-based IPC for AI agents |