RubyGems Guides

What is a gem?

Structure of a Gem

Each gem has a name, version, and platform. For example, the rake gem has a 0.8.7 version (from May, 2009). Rake’s platform is ruby, which means it works on any platform Ruby runs on.

Platforms are based on the CPU architecture, operating system type and sometimes the operating system version. Examples include “x86-mingw32” or “java”. The platform indicates the gem only works with a ruby built for the same platform. RubyGems will automatically download the correct version for your platform. See gem help platform for full details.

Inside a gems are the following components:

Each gem follows the same standard structure of code organization:

% tree freewill
├── bin/
│   └── freewill
├── lib/
│   └── freewill.rb
├── test/
│   └── test_freewill.rb
├── Rakefile
└── freewill.gemspec

Here, you can see the major components of a gem:

More information on the gemspec file

Building your own gem

The Gemspec

Your application, your gem’s users, and you 6 months from now will want to know who wrote a gem, when, and what it does. The gemspec contains this information.

Here’s an example of a gemspec file. You can learn more in how to make a gem.

% cat freewill.gemspec do |s|        = 'freewill'
  s.version     = '1.0.0'
  s.summary     = "Freewill!"
  s.description = "I will choose Freewill!"
  s.authors     = ["Nick Quaranto"]       = ''
  s.homepage    = ''
  s.files       = ["lib/freewill.rb", ...]

For more information on the gemspec, please check out the full Specification Reference which goes over each metadata field in detail.


This guide was adapted from Gonçalo Silva’s original tutorial on and from Gem Sawyer, Modern Day Ruby Warrior.