The paper is a description of a dedicated software for performing the mask layout of diffractive optical elements (DOE). This computer-aided design (CAD) tool is a high productivity tool developed to speed-up the layout process of DOE masks. This utility designs the mask layout, starting from the phase diffraction pattern of DOE expressed as re-usable objects, which are generated by different computing methods and optimization algorithms. The diffraction phase pattern of some frequently used diffraction structures (gratings, lenses), can be computed from the optical parameters entered as input data. The mask layout design can be made for any number of phase levels between 2 and 64, resulting in a set of binary encoding masks. Many DOE functions with the same number of levels can be combined on the same substrate. The mask layout, containing not only the diffractive pattern, but also all the process control patterns needed for manufacturing, is generated in GDS format. The capabilities of this design software are illustrated in an example containing many 4-phase level elements on the same substrate. This CAD mask design software was designed to run on PCs and on SUN Sparc workstations.