Don’t leave home without it. It is inconceivable to do more than a little work in AppleScript and not use this. Don’t the the price dissuade you: it will repay itself month after month, possibly week after week, or even day after day.
UI Browser too. It not only shows UI structure but writes pieces of AppleScript for you.
Really.
Unfortunately (so far), no JXA support. From the web site:
Script Debugger 5 does not support the new JavaScript for Automation feature introduced by Apple in Yosemite (Mac OS X 10.10).
Ironically, we once offered our own JavaScript implementation for Script Debugger versions 2 and 3 and discontinued it due to lack of interest. We are watching how much adoption Apple’s JavaScript for Automation receives. Offering debugging for Apple’s JavaScript implementation is non-trivial so this isn’t something we can easily add back into Script Debugger.
If sufficient interest in JavaScript for Automation develops we will seriously consider adding it to Script Debugger, or possible create a JavaScript specific version of the product.