VS Code Extension Builder

Build professional VS Code extensions with proper architecture, best practices, and complete tooling support.

Quick Start

For immediate extension creation:

1. Initialize: Run npx --package yo --package generator-code -- yo code
2. Choose type: New Extension (TypeScript)
3. Fill details: Name, identifier, description
4. Develop: Open in VS Code, press F5 to debug
5. Test: Run commands in Extension Development Host
6. Package: Run vsce package when ready

For detailed guidance, follow the workflow below.

Extension Types

Choose the type that matches your needs:

• Command Extension: Add commands to Command Palette (simplest, most common)
• Language Support: Syntax highlighting, IntelliSense, formatting
• Webview Extension: Custom UI panels with HTML/CSS/JS
• Tree View: Custom sidebar views with hierarchical data
• Debugger: Add debugging support for languages
• Theme: Color themes, file icon themes
• Snippet Provider: Code snippets for languages

Core Workflow

1. Gather Requirements

Ask user about:

• Purpose: What should the extension do?
• Type: Which extension type? (command, language, webview, etc.)
• Features: Specific functionality needed
• UI: Commands, views, panels, status bar items?
• Activation: When should it activate?

2. Choose Extension Type & Architecture

Based on requirements, select appropriate pattern:

Simple Command Extension (most common):

• Single responsibility
• Command Palette integration
• Quick to build

Language Extension:

• Syntax highlighting (TextMate grammar)
• Language server for IntelliSense
• Complex but powerful

Webview Extension:

• Custom UI needed
• Rich interactions
• More complex state management

See extension-anatomy.md for detailed structure.

3. Initialize Project

Option A: Use Yeoman Generator (Recommended)

npx --package yo --package generator-code -- yo code

Fill in:

• Type: New Extension (TypeScript)
• Name: User-friendly name
• Identifier: lowercase-with-hyphens
• Description: Clear purpose
• Git: Yes
• Bundler: esbuild (recommended) or webpack
• Package manager: npm

Option B: Use Templates

For specific patterns, copy from assets/templates/:

• command-extension/ – Command-based extension
• language-support/ – Language extension starter
• webview-extension/ – Webview-based extension

4. Implement Core Functionality

For Command Extensions:

1. Define command in package.json:

{
  "contributes": {
    "commands": [{
      "command": "extension.commandId",
      "title": "Command Title"
    }]
  }
}

2. Register command in extension.ts:

export function activate(context: vscode.ExtensionContext) {
  let disposable = vscode.commands.registerCommand('extension.commandId', () => {
    vscode.window.showInformationMessage('Hello from Extension!');
  });
  context.subscriptions.push(disposable);
}

For Language Extensions: See common-apis.md for language features APIs.

For Webview Extensions: See common-apis.md for webview creation patterns.

5. Configure Activation & Contributions

Activation Events determine when your extension loads:

• onCommand: When command is invoked
• onLanguage: When file type opens
• onView: When tree view becomes visible
• *: On startup (avoid if possible)

See activation-events.md for complete reference.

Contributions declare extension capabilities in package.json:

• commands: Command Palette entries
• menus: Context menu items
• keybindings: Keyboard shortcuts
• languages: Language support
• views: Tree views
• configuration: Settings

6. Test & Debug

Local Testing:

1. Press F5 in VS Code to launch Extension Development Host
2. Test commands and features
3. Check Debug Console for logs
4. Set breakpoints for debugging

Automated Testing:

• Unit tests: Test business logic
• Integration tests: Test VS Code API interactions
• Use @vscode/test-electron for testing

Common Issues:

• Command not appearing: Check contributes.commands and activation events
• Extension not activating: Verify activation events in package.json
• API errors: Check VS Code API version compatibility

7. Package & Distribute

Prepare for Publishing:

1. Update README.md with features and usage
2. Add extension icon (128×128 PNG)
3. Set repository URL in package.json
4. Add LICENSE file
5. Test thoroughly

Package Extension:

npm install -g @vscode/vsce
vsce package

Creates .vsix file for distribution.

Publish to Marketplace:

vsce publish

Requires Azure DevOps personal access token.

Common Patterns

Pattern 1: Simple Command

Quick command that shows information:

vscode.commands.registerCommand('extension.showInfo', () => {
  vscode.window.showInformationMessage('Information message');
});

Pattern 2: Command with User Input

Get input before executing:

vscode.commands.registerCommand('extension.greet', async () => {
  const name = await vscode.window.showInputBox({
    prompt: 'Enter your name'
  });
  if (name) {
    vscode.window.showInformationMessage(`Hello, ${name}!`);
  }
});

Pattern 3: File Operation Command

Work with active editor:

vscode.commands.registerCommand('extension.processFile', () => {
  const editor = vscode.window.activeTextEditor;
  if (!editor) {
    vscode.window.showErrorMessage('No active editor');
    return;
  }
  
  const document = editor.document;
  const text = document.getText();
  // Process text...
});

Pattern 4: Status Bar Item

Show persistent status:

const statusBarItem = vscode.window.createStatusBarItem(
  vscode.StatusBarAlignment.Right,
  100
);
statusBarItem.text = "$(check) Ready";
statusBarItem.show();
context.subscriptions.push(statusBarItem);

Reference Navigation

Load these references as needed:

• extension-anatomy.md: When you need details about:

  • Extension structure and file organization
  • package.json manifest fields
  • Entry point and lifecycle hooks
  • Extension context and disposables

• common-apis.md: When implementing:

  • Window and editor operations
  • Workspace and file system access
  • Language features (IntelliSense, diagnostics)
  • Webview creation and messaging
  • Tree views and custom UI

• activation-events.md: When configuring:

  • When extension should load
  • Performance optimization
  • Lazy loading strategies

• best-practices.md: When considering:

  • UX guidelines and design patterns
  • Performance optimization
  • Security considerations
  • Testing strategies
  • Publishing guidelines

Key Principles

Performance

• Lazy load: Use specific activation events, not *
• Async operations: Use async/await for I/O
• Dispose resources: Clean up subscriptions
• Minimize startup: Defer heavy operations

User Experience

• Clear commands: Descriptive titles and categories
• Feedback: Show progress for long operations
• Error handling: Helpful error messages
• Consistent UI: Follow VS Code conventions

Code Quality

• TypeScript: Use strict mode for type safety
• Error handling: Try-catch for all operations
• Logging: Use console.log for debugging
• Testing: Write tests for critical functionality

Troubleshooting

Extension Not Appearing

• Verify package.json syntax (valid JSON)
• Check main field points to compiled output
• Ensure activation events are correct
• Reload window: Developer: Reload Window

Command Not Working

• Check command ID matches in package.json and code
• Verify activation event includes the command
• Check Debug Console for errors
• Ensure command is registered in activate()

Build Errors

• Run npm install to install dependencies
• Check TypeScript configuration
• Verify VS Code API version compatibility
• Update @types/vscode if needed

Examples by Use Case

Add Command to Format Code

1. Type: Command extension
2. Activation: onCommand
3. Implementation: Get editor text, format, replace
4. UI: Command Palette entry

Add Syntax Highlighting

1. Type: Language extension
2. Activation: onLanguage:mylang
3. Implementation: TextMate grammar in JSON
4. UI: Automatic on file open

Add Custom Sidebar View

1. Type: Tree view extension
2. Activation: onView:myView
3. Implementation: TreeDataProvider interface
4. UI: Activity bar icon + sidebar panel

Add Quick Pick Menu

1. Type: Command extension with UI
2. Activation: onCommand
3. Implementation: showQuickPick with items
4. UI: Searchable dropdown menu

Resources in This Skill

• references/: Detailed documentation (load as needed)
• assets/templates/: Starting templates for common patterns
• Official docs: https://code.visualstudio.com/api

Related Skills

For code quality and architecture review of your extension code:

• detect-code-smells: Check extension code quality
• security-pattern-check: Security review for extensions
• suggest-performance-fix: Optimize extension performance

Notes

This skill provides the complete workflow for VS Code extension development, from initial concept to published extension. Use progressive disclosure: start with Quick Start for simple cases, dive into references for complex requirements. Templates in assets/ provide copy-paste starting points for common patterns.