Shape grammars play an important role in a new generation of tools for the analysis and design of products. In this work we present a general tool named Shape Grammar Interpreter (SGI) for the automatic generation of designs. The developed shape grammar framework allows designers to obtain automatically generated designs and to participate in the design process. In that way the generated design complies with both the desired functionality and an attractive aspect. Great effort has been devoted on having a comfortable way of defining shapes and later using them in shape grammar rules and designs' generation process. We have also implemented and incorporated in the tool an optimized subshape detection algorithm. Hence, subshapes of the existing shapes can be detected in the generation process obtaining more appealing designs. Keywords-shape grammars; electronic institution; virtual world; 3D; interpreter;