File Extension RB File Format Ruby on Rails class file RB stands for Ruby on Rails class file. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question Apple Mac Air and Ruby on Rails Free Kata Tool - And How To Use Them Translate Ruby Script to SQL Query?