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.cursor/rules/security.mdc

Cursor security rule for Next.js

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 Next.js project. This repository is a Next.js app on the App Router with TypeScript. Server Components are the default. Add a client component only for state, effects, or browser APIs.

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 the App Router, TypeScript, and React Server Components. It does not assume the Pages Router, a database, or an auth library. If the repo already picked one, follow that instead of adding a second.

Customize in the generatorBrowse the library

Example file

Balanced strictness, readable style, pragmatic tests. Download name: security.mdc

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

# Security rules

Attach these rules when editing auth, config, or secret-handling code in this Next.js repository.
This repository is a Next.js app on the App Router with TypeScript. Server Components are the default. Add a client component only for state, effects, or browser APIs.

## Secrets and trust

- Do not put secrets in NEXT_PUBLIC_ variables or client bundles.
- Check auth inside Server Actions and route handlers, not only in the UI.
- Validate search params, headers, and form data before they touch a database.

## Errors

- Fail at the boundary. Do not swallow errors.
- Return a clear error from server actions and route handlers. Do not send stack traces to the client.

## Done when

- Untrusted input is validated before a side effect.
- No secret was added to source, logs, or a client bundle.
- `npm run lint` and `npm test` pass, or you name the command you could not run.

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 Next.js 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 Next.js agent often gets wrong, such as a page that loads data on the server instead of in useEffect. 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 Next.js repo?

Save it at `.cursor/rules/security.mdc` in the Next.js 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 Next.js example assume?

The example assumes the App Router, TypeScript, and React Server Components. It does not assume the Pages Router, a database, or an auth library. If the repo already picked one, follow that instead of adding a second.

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 Next.js

Cursor security rule for other stacks