A committed master.key, one where("name = '#{params[:q]}'") or a missing config.force_ssl is enough to lose your users' data. This skill finds those and nine other Rails mistakes before you deploy, and tells you how to fix each one.

Your agent runs a scanner on your Rails app: config files (secrets.yml, database.yml, environments/production.rb, initializers), controllers, models and ERB views. It skips comments, reads YAML anchors and merges, follows request values (params, cookies, request headers) through variables to the call that uses them, and checks .gitignore before reporting key files. It knows the safe patterns: placeholders and hashes in where, sanitize_sql, permit with a list, link_to, t() and string literals with html_safe. It never runs Ruby or Rails. It returns BLOCK, REVIEW, or NOT FLAGGED, with the file, line, reason, and a safer approach. Secrets are never printed.

What it checks

BLOCK (fix before shipping)

• R01: a literal secret_key_base, password, token or API key for production or staging (YAML or Ruby)

• R02: config/master.key or a credentials .key file that git does not ignore

• R03: request values put into SQL text for where, order, find_by_sql, execute and similar

• R04: permit! or to_unsafe_h (mass assignment)

• R05: request values in system, backticks, eval, constantize, send or render inline

• R06: consider_all_requests_local = true in production

REVIEW (check before release)

• R11: production.rb without config.force_ssl = true

• R12: CSRF protection skipped or turned off

• R13: html_safe on variables, raw, or <%== in views

• R14: redirect_to a URL from params, cookies or the referer

• R15: config.hosts cleared, or CORS origins '*' with credentials

• R16: session or cookies with secure or httponly turned off

What's included

• The scanner (Python 3.9+, standard library only)

• A rules guide with the reason and safer approach for each rule

• A risky and a safe example Rails app, and the real report the scanner produces on the risky one

Limits

It reads code as text, not as a full Ruby parser: values are followed within one file. Gems, credentials.yml.enc contents, Brakeman-level data flow across files and your server setup are not checked. NOT FLAGGED is not a guarantee.

Contents

One ZIP file with 19 files: SKILL.md, the scanner in scripts/ (4 Python files), references/rules.md (every rule with its reason and safer approach), and examples/ (12 example files plus report.md, the real scanner output on the risky example).

How to use: This is an agent skill: a folder with a SKILL.md file and Python scripts that an AI coding agent such as Claude Code, Cursor, or Codex CLI can run. Unzip it into your agent's skills folder (for Claude Code: ~/.claude/skills/), then ask your agent to check your project. The scripts also run on their own with Python 3.9 or newer, with nothing to install. They read your files only: no network access, and nothing is sent anywhere.