Prototyping early in the design process is important for the development of high-quality software. Sketches and wireframes are effective artefacts that inform the design of applications based on Graphical User Interfaces. For applications using speech and Language Technologies (LTC) the Wizard of Oz method aims to fullfil this task. In order to support the demanding task of the wizard, however an optimal wizard interface is desirable. While several wizard interfaces have been built to date, most of them were designed for designated experiments. The possibilities of a generic wizard interface that would address the difficulties of the wizard task across the boundaries of varying experiment settings have remained largely unexplored. In this paper we report on two experiments that aimed at exploring the wizard task in order to inform the design of a univerals wizard interface for testing LTCs.