1. Check if ruby-debug-ide is installed
$ gem list
2. If not installed, install ruby-debug-ide
$ gem install ruby-debug-ide
3. Open the project in Aptana Studio 3, App Explorer -> Gear icon's drop down menu -> Debug Server
4. Set a breakpoint in a file, e.g. index.html.erb
5. Open http://localhost:3000/<your path>/index.html in your browser
6. Aptana will ask you if open Debug perspective. Of cause. You can see the server stops at the break point.
