A software tool was developed to design aeroengine combustors on a preliminary level. Only a small set of input parameters is required to design conventional as well as lean combustors. During the design calculation the combustor contour, the geometry of the desired cooling concept and the air flow distribution within the combustor are optimized. Optimization targets are to minimize the cooling air consumption with respect to the material temperature limits and to reach homogeneous material temperatures as well as a stable combustion. In the case of a staged burner the burner air and fuel fractions are optimized regarding minimal NO x production (qualitative) for the design condition. Off-design calculations on the basis of designed combustors can be executed for engine conditions other than take-off to calculate the altered conditions within the combustor. This paper shows the design and off-design process of the combustor tool in detail. In a second part application examples are given. The presented results show the capabilities of the tool for the pre-design of lean combustors with respect to the trade-off between the reduction of NO x emissions and the reduction of the fuel consumption as well as the capabilities for identifying potential cooling issues.