Its brilliant. It gives you a quick breakdown of what the site is made up of.
My personal fav is that it tells you which theme a Wordpress site is using upfront also shows the extensions used.
Must have for marketers / anyone interested in webdesign.
This is a fun, little Chrome and Firefox add-on that doesn't take up much space, but tells you a lot of valuable information about what services run a website you search! I added the add-on to Chrome > navigate to a Website > click the WhatRuns Icon on my Chrome toolbar and voilà > see what runs! Learn a website's Analytics provider, Web Server, OS, Programming Language, and more! I like the clickable links to learn more, and that you can subscribe to sites. Check out their website and look up the Bug Bounty program: It's a simple idea that "rewards researchers for their efforts in finding out vulnerabilities in our (WhatRuns) product.