Abstract: A utility program develops and updates an API-translation layer of an emulator for running programs written for one platform on another platform. This speeds the development of code such as operating-systems upgrades, where the API set can change frequently. The utility builds a module for each API from a set of templates to execute the module's function on the other platform. Generalized function templates iterate through API functions. Exception templates can override the generalized templates in specific cases. Types templates convert individual arguments of the API. Code templates contain code for incorporation into a number of other templates.