Top-down cracking has been found to be a predominant mode of distresses of asphalt pavements in Florida. Therefore, it is important to accommodate top-down cracking in the design of asphalt mixtures and pavement structures. After a multiyear study on top-down cracking supported by the Florida Department of Transportation, the University of Florida developed a top-down cracking model based on hot-mix asphalt fracture mechanics. This paper presents the implementation of the Florida cracking model into a mechanisticempirical (M-E) flexible pavement design framework. Based on the energy ratio concept, a new M-E pavement design tool for top-down cracking has been developed. In the Level 3 M-E design, a series of semiempirical models were developed for estimation of time-dependent material properties. With incorporation of the material properties models, the design tool is capable of performing pavement thickness design as well as pavement life prediction for top-down cracking in Florida. The thickness design is optimized for different traffic levels, mixture types, and binder selections, and the optimization is an automated process. This design tool has been packed into Windows-based software, making it convenient to use for pavement design engineers.