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Our recommendation on the use of “_” and “-“ in your gem’s name.

Here are some examples of our recommendations for naming gems:

Gem name Require statement Main class or module
ruby_parser require 'ruby_parser' RubyParser
rdoc-data require 'rdoc/data' RDoc::Data
net-http-persistent require 'net/http/persistent' Net::HTTP::Persistent
net-http-digest_auth require 'net/http/digest_auth' Net::HTTP::DigestAuth

The main goal of these recommendations is to give the user some clue about how to require the files in your gem. Following these conventions also lets Bundler require your gem with no extra configuration.

If you publish a gem on it may be removed if the name is objectionable, violates intellectual property or the contents of the gem meet these criteria. You can report such a gem to via email.

Use underscores for multiple words

If a class or module has multiple words, use underscores to separate them. This matches the file the user will require, making it easier for the user to start using your gem.

Use dashes for extensions

If you’re adding functionality to another gem, use a dash. This usually corresponds to a / in the require statement (and therefore your gem’s directory structure) and a :: in the name of your main class or module.

Mix underscores and dashes appropriately

If your class or module has multiple words and you’re also adding functionality to another gem, follow both of the rules above. For example, net-http-digest_auth adds HTTP digest authentication to net/http. The user will require 'net/http/digest_auth' to use the extension (in class Net::HTTP::DigestAuth).

Don’t use UPPERCASE letters

OS X and Windows have case-insensitive filesystems by default. Users may mistakenly require files from a gem using uppercase letters which will be non-portable if they move it to a non-windows or OS X system. While this will mostly be a newbie mistake we don’t need to be confusing them more than necessary.


This guide was expanded from How to Name Gems by Eric Hodel.