RuboCop
Ruby static analysis and linting tool — enforces Ruby community style guide via configurable 'cops' that check style, layout, lint, metrics, naming, performance, and security. RuboCop features: rubocop CLI with auto-fix (--autocorrect), .rubocop.yml configuration, department-based cop organization (Style, Layout, Lint, Metrics, Naming, Security), extension gems (rubocop-rails, rubocop-rspec, rubocop-performance), AllCops settings for include/exclude, inheritance from shared config (rubocop-rails, rubocop-ast), and integration with editors and CI. Example cops: Style/StringLiterals (single vs double quotes), Metrics/MethodLength (max 10 lines), Lint/UnusedVariable, Security/Eval. The de facto Ruby style enforcer used by Rails, Homebrew, and most major Ruby projects.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Local static analysis — no network access during analysis. Remote config (inherit_from URL) fetches configuration over HTTPS; pin config version to avoid malicious config injection in agent CI. RuboCop Security department catches Security/Eval, Security/MarshalLoad, Security/YAMLLoad in agent Ruby code.
⚡ Reliability
Best When
Every Ruby and Rails agent project — RuboCop is the universal Ruby linting standard with community-agreed default rules and Rails-specific extensions.
Avoid When
There is no scenario to avoid RuboCop — include it in every Ruby agent project. Customize .rubocop.yml to match team preferences rather than disabling entirely.
Use Cases
- • Agent codebase style enforcement — rubocop --autocorrect app/services/agent_service.rb fixes auto-correctable style issues; CI runs rubocop --no-color --format progress to fail on violations; enforces consistent Ruby style across agent developer team
- • Rails agent app with rubocop-rails — add gem 'rubocop-rails' and require: rubocop-rails in .rubocop.yml; Rails-specific cops like Rails/FindEach (use find_each for large agent datasets) and Rails/TimeZone enforce Rails best practices
- • RSpec agent test linting — rubocop-rspec extension adds RSpec-specific cops: RSpec/DescribeClass, RSpec/ExpectChange, RSpec/MessageExpectation; ensures agent spec files follow RSpec style conventions alongside general Ruby style
- • Agent metrics control — Metrics/MethodLength: Max: 20 and Metrics/ClassLength: Max: 200 in .rubocop.yml sets project-specific thresholds; agent service classes exceeding limits get rubocop violation flagging need to refactor
- • Security cop for agent code — Security/Eval and Security/MarshalLoad cops flag dangerous Ruby in agent code; rubocop --only Security runs security-specific cops as lightweight SAST in agent CI pipeline
Not For
- • Deep security scanning — RuboCop security cops catch obvious patterns; for comprehensive agent code security use Brakeman (Rails-specific SAST) or Semgrep
- • Runtime type checking — RuboCop does static analysis only; for Ruby type checking use Sorbet or Steep with RBS type signatures
- • Non-Ruby files — RuboCop analyzes .rb files only; for ERB templates use erb-lint; for Haml use haml-lint
Interface
Authentication
No auth — local CLI static analysis tool.
Pricing
RuboCop is MIT licensed. All official extension gems (rubocop-rails, rubocop-rspec, rubocop-performance, rubocop-ast) are open source.
Agent Metadata
Known Gotchas
- ⚠ AllCops NewCops: enable required for new cops — RuboCop adds new cops in minor versions as 'pending' (disabled by default); without NewCops: enable in .rubocop.yml, new cops never run; agent CI passing with outdated cop set misses new violations; add NewCops: enable and periodically review new cop violations
- ⚠ rubocop-rails requires separate gem and require — add gem 'rubocop-rails', require: false to Gemfile; add require: rubocop-rails in .rubocop.yml; missing require means Rails cops like Rails/TimeZone silently don't run; agent Rails projects think they're getting Rails cop coverage when they're not
- ⚠ --autocorrect-all vs --autocorrect — --autocorrect only fixes 'safe' auto-corrections; --autocorrect-all (formerly --auto-correct-all) fixes unsafe corrections too; some unsafe fixes change agent code behavior (Style/HashTransformValues); review unsafe corrections before committing to agent codebase
- ⚠ Metrics cops use method/class size not complexity — Metrics/MethodLength counts lines including blank lines and comments; 10-line default is aggressive for agent service methods; set Metrics/MethodLength: Max: 20 and Metrics/AbcSize: Max: 30 for realistic thresholds before disabling; many teams disable Metrics cops entirely
- ⚠ Inheriting from external shared config — inherit_from: https://raw.githubusercontent.com/org/rubocop-config/main/.rubocop.yml allows shared team .rubocop.yml; remote configs are cached locally; agent CI must cache rubocop config or face network dependency; use inherit_gem: rubocop-my-gem for bundled shared config instead
- ⚠ rubocop-rspec version must match rubocop version — rubocop-rspec 3.x requires rubocop 1.65+; mismatched versions cause LoadError or missing cop departments; agent projects updating rubocop must simultaneously update rubocop-rspec and rubocop-rails to compatible versions in Gemfile
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for RuboCop.
Scores are editorial opinions as of 2026-03-06.