I can’t even calculate the number of hours Xylescope saved me in web development. Frankly it is an awesome app and the developers are extremely responsive and helpful. Xylescope is a simple use of the Webkit browser code with heavy duty CSS analysis built-in so you can see what CSS rules are being used live. Just awesome. And now free.
Migration Score
GOOD
Migration Options
Firebug
As good or better than any web debugging tool I've ever used, Firebug is now the gold standard in this arena. It's a free Firefox extension that makes Xylescope look like a nice toy.