sinatra-url-for constructs absolute paths and full URLs for handlers in a Sinatra application. Assuming that your application is running on example.com, and that it has been mapped to /myapp, you should be able call url_for from within a handler as follows: url_for "/" # Returns "/myapp/" url_for "/foo" # Returns "/myapp/foo" url_for "/foo", :full # Returns "http://example.com/myapp/foo"