We present a novel optical design tool that makes use of an evolutionary global optimization algorithm. The algorithm has several characteristics that make it well-suited for freeform optics design. With the design tool it is no longer necessary to make the distinction between paraxial degrees of freedom and degrees of freedom related to freeform surface description. The design process, which typically involves a multi-stage scheme consisting of finding an optimal paraxial starting layout, optimization, gradually including freeform degrees of freedom to yield an optimal nominal design, and finally a step in which the as-built design is optimized, is shortened because optimal paraxial starting point and optimal freeform shapes are combined to a single optimization step. Optionally, as-built performance can be included in this step as well. The design tool is applied to the design of a compact spectrometer.