I’m not sure if I’ve posted this before, but Thomas Frank’s JSON editor is an absolute lifesaver. Enter your JSON code and the editor visualizes it as a tree, complete with features to add & delete nodes.

Available as a download as well as a web app. Absolutely fantastic stuff.

W3C’s new unified validator that can check feeds, stylesheets and XHTML/HTML markup at once.

A simple but really useful tool by Jacob Bijani that generates CSS border radius markup for Gecko, WebKit & CSS3.

Fantastic tool by Dominique Hazaël-Massieux for web developers/programmers.

Much improved. The team has posted a video detailing how to use the new features.

A Google Labs product. Includes a pretty feature-rich browser extension for Firefox.