Bundler

Dependency manager for Ruby projects that tracks and installs the exact gems and versions needed across development, staging, and production. Declare dependencies in a Gemfile and run bundle install to resolve and lock them in Gemfile.lock, ensuring everyone on the team and every deployment uses identical gem versions.

Bundler is the default package manager for Ruby, shipped with the language since 1.9, and used by virtually every Ruby and Rails application. It differs from ad-hoc gem installs by enforcing a deterministic lockfile: once Gemfile.lock exists, bundle install reproduces the same dependency graph everywhere, avoiding version drift and compatibility surprises. Compares favorably to tools like npm or pip by treating the lockfile as a first-class, committed artifact that defines the whole dependency tree.

Key capabilities:

• Gemfile for declaring dependencies with version constraints, including pessimistic ~> ranges
• Gemfile.lock for deterministic installs and reproducible builds
• Multiple gem sources and private gem servers alongside rubygems.org
• Dependency groups for separating development, test, and production gems
• Built-in commands for install, update, exec, and running gem-provided binstubs
• Integrates with RubyGems for publishing and installing gems from the ecosystem

Ruby and Rails teams rely on Bundler to onboard new developers with a single bundle install, keep CI and production in sync with development, and manage complex gem sets across monolithic and modular applications. Gem authors use it to declare and test their own dependencies before publishing.