This is an engine gem for Paul's diagnostic tool “paul_diagnostic” written by Andrew Kim.
The diagnostic page can be accessed via /diagnostic.
NOTE FOR REFINERY APPS: The 'mount Refinery::Core::Engine' line in the routes.rb file of a Refinery CMS application gobbles up everything in its path, leaving no room for gem routes which are loaded after. Therefore, the line
match '/diagnostic', to: 'diagnostic#diagnostic'
must be inserted BEFORE the mount occurs in the applications routes.rb file if running Refinery CMS. (in general, any route must be named before the mount in a Refinery app, and I do not think this is possible in a gem.)