Preview As You Document→
With the new dynamic documentation server in YARD 0.6, you can now see exactly what YARD sees as you document your code. Simply type
yard server --reload to have your project watch for changes in your codebase everytime you refresh the page. With this functionality, you almost have no excuse not to write documentation!
Support Your Own DSL→
You can write all kinds of extensions in YARD, including ones that can understand all of the dynamic magic your framework does in its own little Doman Specific Languages (DSLs). Most importantly, it's really easy to do! There are already plugins that support frameworks like RSpec, DataMapper, Sinatra, and support for others are in the works.
Easily Customize Templates→
YARD is the only Ruby documentation tool that supports storing metadata alongside your documentation. This metadata can be used to create consistent documentation in any format you wish. YARD also comes with a powerful templating system to quickly modify existing templates. And for the simple case, you can even add custom metadata to your docs with nothing but the command-line.
Extend, Extend, Extend!→
YARD already has a handful of really great extensions, and that number is growing every day. YARD has tools to check your documentation quality (and coverage), run inline RSpec tests, test your documentation example code, add "git blame" support to your source listings, graphs to your documentation, even one to document Perl code!