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.cursor/rules/security.mdc

Cursor security rule for Rails

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 Rails project. This repository is a Ruby on Rails app. Follow the conventions already in the repo: MVC, migrations, and strong parameters. Do not introduce a second frontend stack.

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 a Rails app that uses migrations and Active Record. It does not assume Hotwire, React, or a particular auth gem. If the repo has chosen one, stay with it.

Customize in the generatorBrowse the library

Example file

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

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

# Security rules

Attach these rules when editing auth, config, or secret-handling code in this Rails repository.
This repository is a Ruby on Rails app. Follow the conventions already in the repo: MVC, migrations, and strong parameters. Do not introduce a second frontend stack.

## Secrets and trust

- Permit an explicit list of parameters. Never `permit!` on a public action.
- Authorize with the app's existing policy layer before updating a record.
- Keep secret_key_base and API tokens out of the repository.

## Errors

- Fail at the boundary. Do not swallow errors.
- Use model validations and a 4xx response for bad input. Unexpected errors belong in the Rails logger.

## Done when

- Untrusted input is validated before a side effect.
- No secret was added to source, logs, or a client bundle.
- `bin/rails test` passes, and `db:migrate` applies cleanly when the schema changed.

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 Rails 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 Rails agent often gets wrong, such as a controller action that permits only the intended parameters. 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 Rails repo?

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

The example assumes a Rails app that uses migrations and Active Record. It does not assume Hotwire, React, or a particular auth gem. If the repo has chosen one, stay with it.

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 Rails

Cursor security rule for other stacks