source "https://deploy:[email protected]" puts your gem server password in every clone of the repository, and a git_source with "https://#{ENV["GITHUB_TOKEN"]}@github.com/..." looks safe until Bundler writes the real token into Gemfile.lock. This skill finds those and nine other Bundler mistakes before your next bundle install, and tells you how to fix each one.

Your agent runs a scanner on your Gemfiles (Gemfile, gems.rb, Gemfile.next, gemfiles/*.gemfile), Gemfile.lock, .gemspec files and the project's .bundle/config. It skips Ruby comments, follows #{...} inside strings, knows Bundler's github:, gist:, bitbucket: and git_source shorthands and its source, git and path blocks, tells an application from a gem, and reads .gitignore so an ignored .bundle/config or Gemfile.lock is judged correctly. It never runs Ruby or Bundler. It returns BLOCK, REVIEW, or NOT FLAGGED, with the file, line, reason, and a safer approach. Passwords and tokens are never printed.

What it checks

BLOCK (fix before shipping)

• G01: gem sources, mirrors and git gems over http:// or git://, and ssl_verify_mode 0

• G02: passwords and tokens in source or git URLs, in a Gemfile, a gemspec or Gemfile.lock

• G03: gem server credentials in a .bundle/config that .gitignore does not ignore

REVIEW (check before release)

• G11: git and github gems without ref: or tag:, or with a ref that can move (a branch name)

• G12: more than one global source line (dependency confusion; Bundler 4 refuses such a Gemfile)

• G13: an application without a committed Gemfile.lock

• G14: gemspec runtime dependencies without a version

• G15: path gems outside the project

• G16: Bundler plugins without an exact version

• G17: tokens from ENV in git URLs, which Bundler copies into Gemfile.lock

• G18: gem checksum checks turned off in .bundle/config, or a Bundler 4 lockfile without a CHECKSUMS section

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 project (an app, an admin app and a billing engine, with Gemfiles, lockfiles, a gemspec and .bundle/config), and the real report the scanner produces on the risky one

Limits

It reads each file as written: values from the environment are not resolved, ~/.bundle/config, BUNDLE_ environment variables and CI settings are not read, and gem servers are not contacted. Rails settings and application code are not checked. NOT FLAGGED is not a guarantee.

Contents

One ZIP file with 23 files: SKILL.md, the scanner in scripts/ (5 Python files), references/rules.md (every rule with its reason and safer approach), and examples/ (15 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.