Building & Publishing a Gem

A gem is how Ruby code is shared: a packaged, versioned library anyone can install. Learning to author one turns your useful code into something the whole community can depend on.

Learn Building & Publishing a Gem in our free Ruby course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick…

Part of the free Ruby course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

By the end of this lesson you'll scaffold a gem with bundle gem, write the gemspec, structure lib/, build a package, and publish it to RubyGems.org with semantic versioning.

What You'll Learn in This Lesson

1️⃣ Scaffolding and the Gemspec

bundle gem name generates a standard skeleton: lib/ for code, a .gemspec for metadata, and a version.rb .

The gemspec declares the gem's name, version, files, and dependencies, reading the version from a constant.

2️⃣ Writing lib/, Building, and Publishing

The entry point in lib/ is what users load with require . Then gem build packages it and gem push publishes it to RubyGems.org.

Your turn. Apply a backward-compatible feature bump per semantic versioning, then build the gem.

Walk through scaffolding, coding, versioning, and building a tiny stringy gem end to end.

📋 Quick Reference — Gem Authoring

Practice quiz

What is a Ruby gem?

  • a packaged, distributable Ruby library
  • a web server
  • a CSS file
  • a database table

Answer: a packaged, distributable Ruby library. A gem is a packaged Ruby library you can share, version, and install.

Which command scaffolds a new gem project skeleton?

  • gem new mylib
  • rails g gem mylib
  • bundle gem mylib
  • gem create mylib

Answer: bundle gem mylib. bundle gem mylib generates a standard gem skeleton with lib, gemspec, and tests.

What does the .gemspec file describe?

  • the CSS styles
  • the gem's metadata: name, version, files, and dependencies
  • only the README text
  • the database schema

Answer: the gem's metadata: name, version, files, and dependencies. The gemspec declares the gem's name, version, authors, files, and dependencies.

Where does a gem's Ruby source code conventionally live?

  • the bin/ directory
  • the test/ directory
  • the doc/ directory
  • the lib/ directory

Answer: the lib/ directory. Library code goes under lib/, typically lib/mylib.rb and lib/mylib/.

How is a gem's version number usually defined?

  • in a VERSION constant, e.g. in lib/mylib/version.rb
  • only inside the gemspec as a literal
  • in the Gemfile
  • in config/routes.rb

Answer: in a VERSION constant, e.g. in lib/mylib/version.rb. Convention is a VERSION constant in lib/mylib/version.rb that the gemspec reads.

What does the require keyword do for a gem user?

  • deletes the gem
  • loads the gem's code so its classes are available
  • builds the gem
  • publishes the gem

Answer: loads the gem's code so its classes are available. require "mylib" loads the library so you can use its constants and methods.

Which command builds a .gem package from the gemspec?

  • gem package
  • bundle build
  • rake compile
  • gem build mylib.gemspec

Answer: gem build mylib.gemspec. gem build mylib.gemspec produces a versioned .gem file ready to publish.

Where does gem push publish your gem by default?

  • Docker Hub
  • GitHub Pages
  • RubyGems.org
  • npm

Answer: RubyGems.org. gem push uploads the built .gem to RubyGems.org, the public gem host.

Under semantic versioning, which part changes for a backward-incompatible change?

  • the MINOR number
  • the MAJOR number
  • the build metadata
  • the PATCH number

Answer: the MAJOR number. In MAJOR.MINOR.PATCH, a breaking change bumps the MAJOR version.

What does Bundler help with during gem development?

  • managing dependencies and loading the gem locally for testing
  • deploying to production servers
  • running a database
  • styling HTML

Answer: managing dependencies and loading the gem locally for testing. Bundler installs and manages dependencies and lets you load your gem locally with bundle install or a path.