HTML5 Diagnostics With CSS

Whether you are working with a third party CSS code, or explore weird CSS quirks in your own code, often you have to dedicated some time for lengthy debugging sessions. But there is a little helper for you: Holmes makes it easy to find errant mark-up.

Essentially, the tool a diagnostic CSS style sheet that highlights possibly invalid or erroneous mark-up. Just add a single class, and it will create a red border around errors, a yellow border around warnings and a gray border around deprecated styles. In addition to the downloadable CSS style sheet, there's also a Holmes bookmarklet that lets you apply holmes.css to any page in your browser.