A method and system for controlling access to various tiers of functionality of core software are provided. A software developer/vendor can develop a single version of software having one or more limited-access functionalities and provide the single version of the software to various types of customers. Each customer, using the single version of the core software, may develop additional software that utilizes one or more functionalities of the core software as authorized by the software developer/vendor. Access to a certain functionality or set of functionalities by the customer developed software is obtained by adapting the customer developed software to submit a key, provided by the software developer/vendor, to the core software through, for example, an application programming interface (API) of the core software. The core software is adapted to verify the provided key and, if the provided key is correct, allow the customer developed software access to the corresponding one or more functionalities of the core software.