One of the most powerfull rails tools (and one I use a lot) is rails console. It allows to test functionality with no necessity of a rails server execution, to perform some queries with rails syntax (not in sql), or to modify the information stored in the system, because all changes made in console are stored directly to database.
However, sometimes we need the changes not to be permanent, but only while we are in rails console session. For that, we can execute it adding --sandbox as parameter in prompt. Thus, all changes we made will be rolled back when we leave the console.