IMPORTANT: The YUI library is no longer actively maintained. Please see this announcement for more information.
YUI's lightweight core and modular architecture make it scalable, fast, and robust. Built by frontend engineers at Yahoo!, YUI powers the most popular websites in the world.
YUI's intuitive and well-documented API takes you from basic DOM handling to building performant and maintainable applications on desktop browsers, mobile devices, and servers.
A thriving community, a carefully architected infrastructure, and a comprehensive suite of tools help you code like a pro, from simple web pages to complex web applications.
YUI is free for all uses and is developed in the open on GitHub. Core team members can always be found in the forums and the #yui IRC channel on Freenode. Pull requests welcome!