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.cursor/rules/project.mdc

Cursor rules for Expo

Cursor rules are a markdown file with a short frontmatter header. Cursor attaches them to the agent so it stops guessing how this repo builds, tests, and styles code. This copy is written for a Expo project. This repository is an Expo React Native app. JavaScript stays portable. Native modules are the ones Expo or the project already configured. Do not eject unless the task says to.

The example uses a balanced, readable style, pragmatic tests, and comments only where the intent is not obvious. Open the generator to make the agent stricter, switch to test-first, quiet the comments, or pick a different file.

The example assumes Expo with React Native. It does not assume Expo Router versus React Navigation unless the repo already picked one. Do not add a bare workflow change casually.

Customize in the generatorBrowse the library

Example file

Balanced strictness, readable style, pragmatic tests. Download name: project.mdc. Legacy path: .cursorrules

---
description: "Working rules for a Expo repository"
globs: "**/*"
alwaysApply: true
---

# Project rules

Follow these rules on every task in this Expo repository.
If the project still uses a root `.cursorrules` file, keep the same rules there.

## Stack

This repository is an Expo React Native app. JavaScript stays portable. Native modules are the ones Expo or the project already configured. Do not eject unless the task says to.

## Layout

- Screens live in the app or src directory the router already uses.
- Shared components stay presentation-only. Data hooks sit beside them.
- Platform-specific files use the `.ios` and `.android` suffixes the bundler already understands.

## Commands

- Dev: `npx expo start`
- Lint: `npm run lint`
- Tests: `npm test`

Use the script the repo already defines when it differs from the command above.

## Conventions

- Use the Expo SDK module that matches the installed SDK. Do not add a raw native library when an Expo module exists.
- Do not import Node built-ins into app code.
- Keep the navigation library the repo already uses.
- Handle the permission prompt the platform requires before using a sensor or the camera.
- Styles use StyleSheet or the utility system the project already has.
- Env vars that ship in the client are public. Treat them that way.

## Testing

Add or update tests when behavior changes.

Test hooks and pure logic in Jest. Do not require a device for a data-transform change.

## Style

- Optimize for the next reader over the shortest diff.
- Comment only when the why is non-obvious.
- Name things the way neighboring files already do.
- Do not reformat code you did not change.

## Errors

- Fail at the boundary. Do not swallow errors.
- Show a recoverable error state on the screen. Do not leave a rejected promise unhandled on launch.

## Scope

- Do the requested task. Do not refactor unrelated code.
- Match the rigor already in the repo. Fix what you touch.
- Ask one clarifying question only when the task cannot be finished without it. Otherwise state the assumption and continue.

## Avoid

- Do not call a native module at import time.
- Do not store secrets in app.json or an EXPO_PUBLIC_ variable.
- Do not upgrade the Expo SDK as a drive-by.
- Do not assume web, iOS, and Android share one bug.

## Done when

- The requested behavior works.
- The screen renders in Expo and `npm test` passes if the repo has tests.
- The diff stays inside the task.
- You list anything you could not run.

Add it to the project

  1. 01

    Copy a starting file

    Copy the example Cursor rules on this page, or open the generator if you want different testing, strictness, or comment rules.

  2. 02

    Save it at .cursor/rules/project.mdc

    Save it at `.cursor/rules/project.mdc` in the Expo repo and create the folders if they are missing. If the project still uses one root rules file, save the body as `.cursorrules`.

  3. 03

    Start a fresh agent session

    Rules files are read when a session starts. A chat that is already open may still be using the old instructions.

  4. 04

    Give it one small task

    Ask for one change a Expo agent often gets wrong, such as a screen that uses a native module the project already depends on, with a loading state. If it ignores the file, confirm the path and start a new session.

Questions about this file

Where do I put Cursor rules in a Expo repo?

Save it at `.cursor/rules/project.mdc` in the Expo repo and create the folders if they are missing. If the project still uses one root rules file, save the body as `.cursorrules`.

Which tools read this Cursor rules?

Cursor reads `.cursor/rules/*.mdc` and, on older setups, a root `.cursorrules` file. Other tools ignore the frontmatter, so use AGENTS.md when more than one agent edits the repo.

What does the Expo example assume?

The example assumes Expo with React Native. It does not assume Expo Router versus React Navigation unless the repo already picked one. Do not add a bare workflow change casually.

Does VibeSpell upload my repository?

No. Recipe pages are static, and the generator builds the file in your browser from the options you pick. Your source code never leaves the machine.

Other files for Expo

Cursor rules for other stacks