XRAY is a free cross browser tool that lets you see the box model in action for any element, letting you see beneath the skin of any web page. Just click the XRAY button to instantly answer those vital questions: where is the top and left of this element? how big is each margin? how big is the padding? how wide and high is the content box? XRAY works just like any other bookmarklet. To install it, normally you would just drag the box marked XRAY below to the bookmarks bar in your web browser. In some browsers bookmarklets work differently: just do whatever you would normally do to create a bookmark for whatever is linked to the XRAY box below.

Requirements: Any Browsers Except Internet Explorer and Opera
Demo: http://westciv.com/xray/xray_more.html#step2
License: Open Source License