Computational tools for building and editing mechanistic- and pathways-level kinetic models for fluid catalytic cracking were developed. A special emphasis was placed on the relationship between the mechanistic- and pathways-level models. Mechanistic models incorporate more fundamental kinetic information and hence have a wider range of applicability. Their main drawback is the explosion in the number of molecular and intermediate species and the mathematical stiffness associated with the relative time constants of these types of species. These issues are absent in pathways-level models, which leads to a dramatic reduction in the solution time and justifies their use for cases of practical interest, but this usually is accompanied by the loss of some chemical significance. The practical resolution of this conflict was to guide the development of the pathways level model by mechanistic insights into the fluid catalytic cracking chemistry, including the solution of mechanistic kinetic sequences for carbenium ion and free radical driven cycles. Catalyst deactivation by coking was also incorporated.