Language Technology (LT) based applications become more popular as technology improves. Prototyping early in the design process is critical for the development of high quality applications. It is difficult, however, to do low-fidelity prototyping (e.g. paper prototyping) of applications based on LT. One technique that has been used for this kind of prototyping is Wizard of Oz (WOZ). However, this generally involves the development of one-off user and wizard interfaces. A tool that facilitates the flexible integration of LT components into WOZ experiments is desirable. In this paper we explore the requirements for such a tool, drawing from the literature and a first WOZ experiment in which different wizards were observed and their behaviour was analysed. Author Keywords Wizard of Oz; Prototyping; Language Technology. ACM Classification Keywords H.5.2 User Interfaces: Prototyping; H.5.2 User Interfaces: Natural Language; D.2.2 Design Tools and Techniques: Modules and interfaces. Ge...