Cursor’s Agent mode (called Composer in some versions) lets you give multi-step tasks to an AI that can read, write, and navigate your entire codebase. Used well, it can cut hours of work to minutes. Used badly, it introduces hard-to-reverse changes.

This guide covers what actually works.

What Agent Mode Is

Agent mode is different from Cursor’s Tab autocomplete. Tab predicts your next edit as you type. Agent mode takes a natural language task — “add JWT authentication to this Express app” — and executes it across multiple files, reading your codebase as needed.

Open it with Cmd+I (Mac) or Ctrl+I (Windows/Linux), or click the Composer icon in the sidebar.

Step 1: Give It Context Before the Task

The single biggest lever in Agent mode quality is context. Before writing your task prompt, tell Cursor what to look at:

  • Type @codebase to let Cursor search across your whole project
  • Type @filename.ts to focus on a specific file
  • Type @folder/ to include a directory

Good prompt:

@src/auth/ @src/middleware/

Add rate limiting to the login endpoint. Use express-rate-limit,
5 attempts per 15 minutes per IP. Return 429 with a Retry-After header.

Bad prompt:

Add rate limiting

The bad prompt forces Cursor to guess where login logic lives. The good prompt gives it a starting point.

Step 2: Review the Plan Before Execution

After you submit a complex task, Cursor will usually show a plan — a list of files it intends to touch and what it plans to do. Read this before clicking Accept.

Red flags to watch for:

  • It’s touching files unrelated to your task
  • The plan involves creating new packages you didn’t ask for
  • It says it will “refactor” something you didn’t mention

If you see any of these, cancel and rewrite the prompt with tighter scope.

Step 3: Review Diffs File by File

When Agent mode finishes, it shows diffs for each changed file. Don’t click “Accept All” without reading.

What to check:

  • Did it change things outside your requested scope?
  • Did it remove existing logic without a clear reason?
  • Does the new code match the style of the surrounding code?

If a diff looks wrong, you can reject individual file changes and ask Agent to redo just that file.

Step 4: Run Your Tests After Every Agent Run

Agent mode gets the happy path right most of the time. Edge cases and existing tests are where it slips up.

After every agent run:

npm test
# or
pytest
# or whatever your test command is

If tests fail, paste the failure output back into the Composer and ask it to fix them. Don’t manually hunt through the agent’s changes — let it fix its own mistakes.

Common Pitfalls

Pitfall 1: Scope creep
Agent mode will sometimes “improve” things you didn’t ask it to touch. This causes bugs in unrelated features. Fix: use @ context to limit what it sees.

Pitfall 2: Hallucinated packages
It occasionally imports packages that don’t exist. Fix: always run your build/test after an agent run before doing anything else.

Pitfall 3: Loop behavior
On complex tasks, Agent sometimes gets into a loop — making a change, then reverting it, then making it again. Fix: press Escape to stop the loop, then rephrase the task more specifically.

Pitfall 4: Too much in one prompt
”Rebuild the entire auth system” is too big. Agent mode works best on tasks that touch 1-5 files. Fix: break large tasks into smaller sub-tasks and run them in sequence.

What Agent Mode Is Best At

  • Adding a new endpoint to an existing API (1-3 files)
  • Writing or updating tests for a specific module
  • Migrating one pattern to another across a bounded set of files
  • Debugging: “here’s the error, here are the relevant files, find and fix it”
  • Adding a feature to an existing module where you can point it at the file

What Agent Mode Struggles With

  • Architectural changes across your whole codebase
  • Tasks that require understanding non-code context (business logic, product decisions)
  • Working in large monorepos without tight @ scoping

The Mindset Shift

The developers who get the most out of Agent mode treat it like a junior engineer: capable, fast, but needs clear instructions and a review before their work ships. The developers who get burned by it treat it like a magic box.

Give it context, define scope, review the output, run your tests. That’s the whole workflow.