RuboCop

Free plan LinuxSelf-hosted

What RuboCop is

RuboCop is free, open-source software for analyzing and formatting Ruby code according to the community Ruby Style Guide. Its checks, called cops, cover bugs, style, layout, naming, complexity, and security. Many findings can be corrected automatically, with separate controls for safe fixes and changes that may affect behavior. Teams configure rules in .rubocop.yml, inherit shared settings, and use --auto-gen-config to record existing offenses in .rubocop_todo.yml. Plugins extend checks for frameworks and libraries, including Rails, RSpec, Minitest, and Capybara. The built-in language server can display offenses while typing and format on save in VS Code, RubyMine, Emacs, Neovim, Helix, and Zed. GitHub output can annotate pull requests, SARIF feeds code scanning, and JUnit output supports CI. RuboCop also supports coding-agent inspection through the Model Context Protocol and can limit checks to changed files.

Who it suits

RuboCop suits Ruby teams wanting automated style, bug, complexity, and security checks. It also fits projects that need editor feedback, CI output, configurable rules, or gradual cleanup of existing offenses.

What it does well

Free open-source Ruby analysis
Autocorrection offers safe and behavior-changing modes
Plugins support Rails and other frameworks
Language server supports multiple editors
Outputs formats for CI and code scanning

What to know first

Supports one programming language
Official runtime support starts at MRI Ruby 2.7
Some autocorrections may change behavior
Runs on Linux and self-hosted platforms

Plans

Plan	Billed and limits	Price
RuboCop	Free software; Ruby code analysis and formatting	Free

As rubocop.org lists them, read 10 Oct 2026. The maker's own page has the final word.

Verdict

RuboCop provides configurable Ruby linting, formatting, editor integration, and CI reporting at no cost. Its plugin and autocorrection options support both new projects and legacy codebases.

Facts from RuboCop's own pages

Autocorrection: RuboCop can automatically fix many reported problems, with separate options for safe and potentially behavior-changing corrections. · rubocop.org, 10 Oct 2026
Checks: Its cops check for bugs, style, layout, naming, complexity, and security issues. · rubocop.org, 10 Oct 2026
CI and code scanning: GitHub-formatted output can annotate pull requests, SARIF can feed code scanning, and JUnit output can be used by CI. · rubocop.org, 10 Oct 2026
Coding agents: RuboCop supports inspection and autocorrection for coding agents over the Model Context Protocol. · rubocop.org, 10 Oct 2026
Customization: Teams can configure cop styles in a .rubocop.yml file and inherit settings from a shared configuration. · rubocop.org, 10 Oct 2026
Editors: The built-in language server provides offenses while typing and format-on-save in VS Code, RubyMine, Emacs, Neovim, Helix, and Zed. · rubocop.org, 10 Oct 2026
Existing codebases: The --auto-gen-config command records existing offenses in .rubocop_todo.yml so teams can address legacy issues over time. · rubocop.org, 10 Oct 2026
Founded: 2012 · rubocop.org, 28 Sept 2026
History: The homepage says RuboCop began in April 2012 and identifies Bozhidar Batsov as its originator. · rubocop.org, 10 Oct 2026
Installation: RuboCop can be installed with gem install rubocop or added to a Bundler Gemfile as a standalone tool. · github.com, 10 Oct 2026
Maintainers: The homepage describes RuboCop as free and maintained by a small core team of volunteers with help from thousands of contributors. · rubocop.org, 10 Oct 2026
Plugins: Plugins extend RuboCop for frameworks and libraries, and the project lists maintained plugins for Rails, RSpec, Minitest, Capybara, and others. · rubocop.org, 10 Oct 2026
Purpose: RuboCop is a Ruby static code analyzer and formatter based on the community Ruby Style Guide. · rubocop.org, 10 Oct 2026
Runtime support: The repository README says RuboCop officially supports MRI Ruby 2.7 and later and JRuby 9.4 and later, and targets Ruby 2.0 and later for code analysis. · github.com, 10 Oct 2026
Security disclosure: The project repository links to a security policy, but the opened pages do not state a security certification or compliance standard. · github.com, 10 Oct 2026
Selective inspection: The --changed option limits inspection to files that Git reports as changed. · rubocop.org, 10 Oct 2026