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.cursor/rules/security.mdc

Cursor security rule for Expo

A focused Cursor `.mdc` rule for auth, secrets, and untrusted input. It attaches when those files change, instead of repeating security policy in every chat. 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: security.mdc

---
description: "Security rules for a Expo repository"
globs: "**/*{auth,Auth,secret,config,Config}*"
alwaysApply: false
---

# Security rules

Attach these rules when editing auth, config, or secret-handling code in this Expo repository.
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.

## Secrets and trust

- EXPO_PUBLIC_ values are visible in the app binary.
- Store tokens in secure store, not AsyncStorage, when the app already has a secure-store dependency.
- Validate deep-link params before navigating.

## 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.

## Done when

- Untrusted input is validated before a side effect.
- No secret was added to source, logs, or a client bundle.
- The screen renders in Expo and `npm test` passes if the repo has tests.

Add it to the project

  1. 01

    Copy a starting file

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

  2. 02

    Save it at .cursor/rules/security.mdc

    Save it at `.cursor/rules/security.mdc` in the Expo repo. Narrow the globs if your auth and config files live in a known folder.

  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 security rule in a Expo repo?

Save it at `.cursor/rules/security.mdc` in the Expo repo. Narrow the globs if your auth and config files live in a known folder.

Which tools read this Cursor security rule?

Cursor loads `.cursor/rules/security.mdc` for files that match its globs. Pair it with the always-on project rule. It is not a substitute for code review.

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 security rule for other stacks