Luxor is an open-source XML User Interface Language (XUL) toolkit in Java.

Luxor is a free, open-source XML UI Language (XUL) toolkit in released under the GNU General Public License (GPL) that lets you build UIs using XML and includes an ultra-light weight, multi-threaded web server, a portal engine, a template engine (Velocity), a scripting interpreter (Python) and more.

XUL stands for XML UI Language and was pioneered by Mozilla. XUL is superior to API-based UI toolkits such as Swing or WinForms because it clearly separates the user interface into four parts:

- content (structure and description of UI elements),
- appearance (look & feel, skin, themes),
- behavior (scripting) and
- locale (localization information for internationalization)

Content is best described in XUL as the following short example illustrates.

XUL makes UI building easier because it is far simpler than hard-wiring it in Java. XUL also frees you from the Swing toolkit lock-in because you can create a new rendering engine using a different UI toolkit such as KDE, Gnome, or WinForms.