Gemfile File — Ruby Dependency File

Gemfile is the dependency specification file for Ruby projects, used by Bundler — the standard dependency manager for the Ruby ecosystem. Gemfiles are written in a Ruby DSL that declares required gems (Ruby packages) with version constraints, source repositories, and grouping. The syntax includes gem declarations (gem 'rails', '~> 7.0'), source specifications (source 'https://rubygems.org'), groups for environment-specific dependencies (group :development, :test do ... end), platform conditionals, and Git/path sources for unreleased gems. Bundler resolves all dependencies (including transitive ones), generates a Gemfile.lock with exact versions, and installs gems into an isolated environment. The bundle exec command ensures scripts run with the correct gem versions. Gemfiles support groups like :development (testing tools, debuggers), :test (testing frameworks), :production (monitoring, error tracking), and :assets (asset pipeline gems). Bundler was revolutionary when introduced in 2010, solving Ruby's dependency management problems and inspiring similar tools in other ecosystems (npm, pip, Cargo). Every Ruby on Rails application uses a Gemfile, and the format is integral to Ruby development workflows, CI/CD pipelines, and Heroku deployment.