This library is called html_tags. Its basic core idea is to collect all valid html tags into a single project, and then make this data available to other projects. Other ideas are to autogenerate closing tags (helper methods), and of course to generate string representations of these html tags. This can then be used by other web-projects. A simple usage example follows: require 'html_tags' HtmlTags.p 'hello world!' # => "<p> hello world! </p>" Since Version 0.0.10 (April 2014) we can also now query whether a string contains only valid HTML tags or whether it does not.