Abstract: A system is disclosed in which a single tool-independent model of a circuit design is used to generate a plurality of tool-specific circuit models suitable for use with a plurality of target tools, such as Automatic Test Pattern Generation (ATPG) tools and/or equivalence tools. A plurality of circuit block class definitions provide abstract interfaces to a plurality of circuit block classes. Each circuit block class definition includes a plurality of tool-specific models of the corresponding circuit block class. The tool-independent circuit model models at least some of the blocks in the circuit design by reference to the circuit block class definitions. A circuit model processor generates a tool-specific circuit model by replacing tool-independent block models in the tool-independent circuit model with corresponding tool-specific block models suitable for use with a particular one of the target tools.