Ruby 101

Jekyll is written in Ruby. If you’re new to Ruby, this page is to help you get up to speed with some of the terminology.


A gem is code you can include in Ruby projects. It allows you to package up functionality and share it across other projects or with other people. Gems can perform functionality such as:


A Gemfile is a list of gems required for your site. For a simple Jekyll site it might look something like this:

source ""

gem "jekyll"

group :jekyll_plugins do
  gem "jekyll-feed"
  gem "jekyll-seo-tag"


Bundler installs the gems in your Gemfile. It’s not a requirement for you to use a Gemfile and bundler however it’s highly recommended as it ensures you’re running the same version of Jekyll and Jekyll plugins across different environments.

gem install bundler installs Bundler. You only need to install it once — not every time you create a new Jekyll project. Here are some additional details:

If you’re using a Gemfile you would first run bundle install to install the gems, then bundle exec jekyll serve to build your site. This guarantees you’re using the gem versions set in the Gemfile. If you’re not using a Gemfile you can just run jekyll serve.

For more information about how to use Bundler in your Jekyll project, this tutorial should provide answers to the most common questions and explain how to get up and running quickly.