In order to respond to the difficulties encountered by CAD software applications in really assisting the conceptual designer, we propose a tool that is capable of interpreting design sketches and feeding data to various project evaluators, right from the early phases in the design process. For that purpose, we use the concept of the absent interface, which is the only interface that is compatible with the cognitive process involved in sketching. In this paper, we present the principles of such an interface, illustrated by EsQUIsE, a software prototype for capturing and interpreting architectural sketches, which has been under development for several years.