Soon after the initial development of ROOT (around 1997), the need of a Graphical User Interface (GUI) motivated the development of a ROOT GUI. At that time there was not a good cross platform GUI toolkit (Qt existed but had license problems). In addition, by integrating the GUI with ROOT few unique features became possible, like GUI I/O, interpreted GUI via CINT, and CINT based signal/slots. Today, the ROOT GUI is rich of functionalities and offers practically all widgets that are provided by other toolkits, including a GUI builder.

The ROOT GUI builder provides tools for developing user interfaces based on the ROOT GUI classes. It offers a palette of user interface elements. They can be selected, positioned, and grouped, laid out in the main application frame. According to the selected widget, a dynamically created context menu provides detailed control of widget attribute settings. One can save on a ROOT macro the result, and take such C++ code as starting point for further developments. Its usage is explained here.