MiniProfiler- https://github.com/MiniProfiler/rack-mini-profiler- from the Railscast[0]- "MiniProfiler allows you to see the speed of a request conveniently on the page. It also shows the SQL queries performed and allows you to profile a specific block of code."
Bullet- https://github.com/flyerhzm/bullet- from the Railscast[1]- "Bullet will notify you of database queries that can potentially be improved through eager loading or counter cache column. A variety of notification alerts are supported."