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Atlas Whoff
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Cursor Editor Power User Guide: Composer, Rules Files, and the Features Most Developers Miss

#claudecode #ai #productivity #webdev

The Cursor editor has become the default for many developers using AI in their workflow. It's VS Code with Claude and GPT-4o deeply integrated. Here's how to actually use it well.

The Three Modes

Cursor has three interaction modes. Most developers only use one.

Tab completion (default): Cursor predicts what you'll type next. Press Tab to accept. This works like Copilot but with more context awareness.

Cmd+K (inline edit): Select code, press Cmd+K, describe the change. Cursor edits only the selected region. Best for: targeted changes to existing code, refactoring a specific function.

Composer (Cmd+I or Cmd+Shift+I): Full-context AI that can read and edit multiple files. Best for: features that span multiple files, understanding a codebase, generating new components.

Most developers use Tab completion constantly, Cmd+K occasionally, and ignore Composer. The Composer is where most of the productivity gain lives.

Composer: How to Use It Well

Open Composer with Cmd+I (normal) or Cmd+Shift+I (full-screen).

@-mention files for context:

@src/lib/auth.ts @src/app/api/users/route.ts 
Add rate limiting to the users route matching the auth pattern
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The @ mentions tell Composer exactly which files to read. Without them, Cursor guesses -- often incorrectly.

@-mention for docs:

@Prisma docs How do I add a composite index?
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Cursor fetches live documentation and uses it in the response.

@-mention for codebase:

@codebase Find all places where we directly query the database 
instead of going through the repository layer
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Searches your entire codebase semantically.

The Rules File

Create .cursor/rules in your project root. Cursor reads it and applies the rules to every Composer session:

# .cursor/rules

## Stack
- Next.js 14 App Router (not Pages Router)
- Prisma + PostgreSQL
- NextAuth v5
- shadcn/ui + Tailwind
- TypeScript strict mode

## Conventions
- API routes: always authenticate first, validate with Zod, return typed responses
- Components: Server Components by default, "use client" only for interactivity
- Database: always filter deletedAt: null, use db singleton from lib/db.ts
- Error handling: log internally, return generic messages to clients

## Patterns
- Auth: see src/lib/auth.ts
- Database: see src/lib/db.ts
- API route pattern: see src/app/api/users/route.ts

## Don't Do
- Don't use Pages Router patterns (getServerSideProps, getStaticProps)
- Don't add "use client" to components that don't need interactivity
- Don't use process.env directly -- use the env singleton at src/lib/env.ts
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This is the Cursor equivalent of CLAUDE.md. Set it once, benefit from it in every session.

Codebase Indexing

Cursor indexes your codebase for semantic search. To make the most of it:

  1. Open the project at the root level -- not a subdirectory. Cursor indexes from where you open.
  2. Wait for indexing to complete (status bar shows progress on first open).
  3. Exclude large generated directories in .cursorignore: 
node_modules
.next
dist
coverage
*.min.js
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After indexing, @codebase searches are accurate. Before indexing, they miss things.

The Chat Panel vs Composer

Chat (Cmd+L): Ask questions, get explanations. Doesn't edit files.

Composer (Cmd+I): Generates and applies code changes.

Use Chat for: "Explain what this function does." "What's the best approach for X?"
Use Composer for: "Implement X." "Refactor Y to do Z."

Model Selection

Cursor lets you choose the model per-session:

  • claude-sonnet-4-6: Best for complex reasoning, large codebase tasks. Default choice.
  • claude-opus-4-6: Best for the hardest problems. Slower and more expensive.
  • GPT-4o: Good alternative if you want diversity.
  • cursor-small: Fast for simple completions. Use for Tab completion.

For Composer tasks: Claude Sonnet 4.6. For Tab completion: let Cursor pick (it uses a fast model automatically).

Privacy Mode

If your codebase is proprietary:
Settings -> Privacy -> Enable Privacy Mode.

With privacy mode on, your code is not used to train models. Without it, Cursor may use code snippets for training.

Common Workflow: Adding a Feature 

1. Open Composer (Cmd+I)
2. @mention the files most relevant to the feature
3. Describe the feature, its constraints, and what it should match
4. Review the diff before applying
5. Run tests (Cursor can do this too if you ask)
6. Accept or reject individual changes
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The key step developers skip: reviewing the diff before applying. Composer shows you every file it wants to change. Read it. Catch the 5% that needs adjustment.

When to Use Claude Code Instead

Cursor is optimized for in-editor work. Use Claude Code when:

  • The task spans many files and requires running commands
  • You need to run tests, migrations, or build steps as part of the task
  • The task takes longer than a few minutes (Claude Code has better session persistence)
  • You need agentic behavior (Claude Code can autonomously execute multi-step plans)

Cursor + Claude Code is a powerful combination: Cursor for fast in-editor work, Claude Code for complex autonomous tasks.

The Ship Fast Skill Pack includes skills tuned for both Cursor workflows and Claude Code sessions.

Ship Fast Skill Pack ($49) ->

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