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Cursor Deep Dive

5 min read

Frontend

Agent mode shines for component refactors and cross-file CSS/component updates.

Backend

Use @codebase for 'find all usages of this function' and 'add error handling here and everywhere it's called.'

Cursor Deep Dive

TL;DR

  • Cursor is VS Code + AI that understands your codebase. The difference is context.
  • Master @-mentions, Agent mode, and custom instructions. They're the force multipliers.
  • Shortcuts matter. You'll use them 50 times a day.

Cursor (as of 2026) is the leading AI-first IDE. It's built on VS Code, so if you know VS Code, you're 80% there. The other 20% is where the leverage is.

Setup: The First 15 Minutes

  1. Install. cursor.com. Sign in.
  2. Index your codebase. Open your project. Cursor indexes in the background. Big repos take a few minutes.
  3. Custom instructions. Cursor Settings → General → Rules for AI. Add role, stack, conventions. Example: "We use TypeScript, prefer functional components, no any. Our API base is /api/v2."

That's the minimum. Do it before you start coding.

The @-Mention System

Cursor's power is context. You tell it what to look at.

MentionWhat It Does
@CodebaseSearch entire project. "Find all places we call getUser"
@FolderScope to a folder. "Refactor everything in /components"
@FileReference a file. "Add error handling like we do in api/utils.ts"
@DocsPull in documentation (web, library docs). "Use the React Query v5 API"
@WebSearch the web. "What's the latest Next.js 15 pattern for server components?"

Pro tip: Combine them. "Using @api/auth.ts and @Codebase, show me all routes that need auth and add the middleware."

Agent Mode: When to Use It

Agent mode lets Cursor take actions: edit files, run terminals, apply changes. It's powerful and a bit dangerous.

Use Agent for:

  • Multi-file refactors ("rename this function and update all callers")
  • Adding a feature across several files ("add logging to all API endpoints")
  • Repetitive edits ("add null checks to every function in this file")

Don't use Agent for:

  • One-off small edits (regular chat + accept is faster)
  • When you're unsure what you want (Agent will guess)
  • Critical files (review every diff)

Keyboard shortcut: Cmd+Shift+I (Mac) or Ctrl+Shift+I (Win/Linux). Or type in chat and click "Agent" when you want it to execute.

Shortcuts Worth Memorizing

ShortcutAction
Cmd+KInline edit — select code, describe change, get diff
Cmd+LOpen AI chat
Cmd+IComposer (multi-file editing)
Cmd+Shift+IAgent mode
TabAccept suggestion / apply edit
EscReject

Cmd+K is the workhorse. You'll use it more than anything else.

Custom Instructions That Actually Help

Generic instructions ("write good code") don't help. Specific ones do.

Good examples:

  • "We use pnpm. Never suggest npm or yarn."
  • "Our API returns { data, error }. Handle both in examples."
  • "Prefer early returns. No nested ifs超过 2 levels."
  • "We use 'id' not 'ID' in variable names."

Bad: "Be concise." (Too vague.)

Common Pitfalls

  • Over-indexing: Don't add your whole monorepo to context if you're working on one service. Use @Folder to scope.
  • Stale index: After big refactors or new files, give it a minute. Or restart Cursor.
  • Agent overreach: If Agent wants to change 20 files and you're nervous, scope it down. "Just do the first 3 files."

You need to add auth middleware to 12 API routes. You manually edit each file. Copy-paste. Fix imports. Realize you missed 2. 45 minutes of tedious, error-prone work.

Click "Cursor @-mentions + Composer" to see the difference →

Quick Check

You need to refactor a function and update all 15 call sites across the codebase. What's the best Cursor approach?

Do This Next

  1. Set up custom instructions with 3 rules for your current project. Test with a simple edit.
  2. Use Cmd+K for your next 5 edits. Get used to describing changes instead of typing them.