CSS Tools is an experiment into how we can improve the CSS telemetry in a browser. The core thinking is that currently browsers do little more than tell you what you have given them. They should be telling you how they understand what you've told them, and more importantly how to do it better.
The idea behind the CSS Doctor is to take the web developer from 'Ga! Why does my element look like that?' to an explanation in as little time as possible. We select an element that looks wrong, and a rule that should make it look right, and explain why the rule isn't affecting the element properly.