Nowadays, the advent of smart devices equipped with the latest input technologies has changed the way users interact with smart devices. The gesture based user interface, as the natural user interface technologies, has attracted a lot of attention from researchers and developers. Gestures can be constituted in different ways; touching a screen, moving a pointing device, or making hand or body movements in a three-dimensional (3D) space. The various gesture input devices make application developers to maintain multiple source code families for the same applications adapting different gesture input devices. In this paper, we defined the gesture interface markup language (GIML) based on extensible markup language (XML) to describe gestures independently of the input devices. It also provides constraints necessary to determine which gesture has occurred and information required when UGesture platform interact with the gesture based application. The proposed GIML is based on our previous implemented the UGesture platform and the evaluation results, and so the GIML can be used to define new gestures for the UGesture platform and support new input hardwares.