You can undo and redo your changes at any time by clicking on the Undo or Redo buttons in the top right corner.
When you make changes, Jibility will retain a list of up to ten (10) changes that you can undo. If you make more than ten changes, then the oldest change is dropped from your undo list.
You can see how many changes are queued and what was your last change in the tool tip when you hover your mouse over the Undo or Redo buttons. In the example below, there is one  change in the undo queue and the last change made was a reordering of a challenge.