Composer is Cursor's most powerful feature — it can plan and execute changes across multiple files simultaneously. Think of it as having an AI pair programmer who can work on your entire project at once.

Opening Composer

Press Cmd+Shift+I (Ctrl+Shift+I) to open Composer. You'll see a full-screen interface where you describe what you want built or changed.

What Composer Can Do

• Create new features spanning multiple files (components, routes, tests, types)
• Refactor code across your project (rename patterns, update APIs, migrate libraries)
• Fix bugs that span multiple files
• Add tests for existing code
• Set up configurations (ESLint, Prettier, CI/CD)

Example: Building a Feature

Prompt: "Add a dark mode toggle to the app. Create a ThemeProvider context, a toggle button component, update the layout to use the provider, and save the preference to localStorage."

Composer will:

1. Create src/contexts/ThemeContext.tsx
2. Create src/components/ThemeToggle.tsx
3. Modify src/components/Layout.tsx to wrap with ThemeProvider
4. Update relevant CSS/Tailwind classes
5. Add localStorage persistence

You review each file change as a diff before accepting.

Giving Composer Context

The better context you provide, the better the results:

• "Using @package.json, update the auth system to use the latest version of next-auth"
• "Based on @src/types/user.ts, create a user profile page with all fields"
• "Following the patterns in @src/components/ProductCard.tsx, create a ServiceCard component"

Composer vs. Chat vs. Cmd+K

Best Practices

1. Start specific: "Add email validation to the signup form" beats "improve the forms"
2. Break large tasks into steps: Don't ask Composer to build your entire app in one prompt
3. Review diffs carefully: AI-generated code can have subtle bugs
4. Iterate: Accept partial results and refine with follow-up prompts
5. Use .cursorrules: Define project conventions so Composer follows your patterns