Bundler .require run TheSmallestRailsApp ||= Class .new( Rails :: Application ) { config.secret_key_base = routes.append { root to : proc { [ 200 , { " Content-Type " => " text/html " }, [ Markaby :: Builder .new.html { title @title = " The Smallest Rails App " h3 " I am # @title ! " p " Here is my source code: " text CodeRay .scan_file( __FILE__ ).div( line_numbers : :table ) p { a " Make me smaller " , href : " //goo.gl/YdRpy " } }]] } }.to_s initialize! }