In one embodiment, a graphical arrangement of one or more interface elements and a definition of one or more events associated with the interface elements is used to build a state diagram model of a graphical user interface (GUI). The state diagram model of the GUI includes a plurality of states, and one or more transitions linking at least some of the states. The state diagram model may be displayed to a user, and in some cases, simulated to test functionality of the GUI. In response to user input, the state diagram model may be modified to change functionality of the GUI and/or to add functionality to the GUI. The GUI may then be generated from the state diagram model.