The core of ZK consists of an Ajax-based event-driven mechanism, over 123 XUL and 83 XHTML-based components,[6] and a mark-up language for designing user interfaces.

Programmers design their application pages in feature-rich XUL/XHTML components, and manipulate them upon events triggered by end user's activity.

ZK uses a server-centric approach in which the content synchronization of components and the event pipe-lining between clients and servers are automatically done by the engine, and Ajax plumbing codes are completely transparent to web application developers.

At the browser, ZK only downloads a JSON description of the web page and uses a client renderer to turn that into a UI.

In addition to component-based programming in a manner similar to Swing, ZK supports a mark-up language for rich user interface definition called ZUML.