Engineering conceptual design can be defined as that phase of the product development process during which the designer takes a specification for a product to be designed and generates many broad solutions for it. It is well recognized that few computational tools exist that are capable of supporting the designer work through the conceptual phase of design. However, significant recent developments have been made in solid modeling and 3D computer-aided design. The use of such tools has become a critical element in the more sophisticated product development processes to be found in modern industry. This paper presents a prototype constraint-based computer-aided design (CAD) technology that can be used to support designers working in the early stages of design. The technology has been developed as an add-in application for Autodesk Inventor, a 3D solidmodeling environment. The add-in has, at its core, a constraint filtering system based on generalised arc-consistency processing and backtrack search. We present our current prototype and a detailed demonstration of its functionality. Finally, we describe our current work on a number of additional features for the next prototype, which will be deployed in an industrial context. © Springer-Verlag 2003.