Abstract: Native operating system application programming interfaces (API's) are described using metadata and such descriptions are stored in a standard file format in a known location. By storing API definitions using such metadata, other applications can readily identify and use the APIs. To create such API representations, during development, a developer describes the shape of the API, including (but not limited to) the classes, interfaces, methods, properties, events, parameters, structures and enumerated types defined by the API. This API description is processed by a tool which generates a machine-readable metadata file. The machine-readable metadata file contains the same information as the API description, however in a format designed to be machine read rather than human authored.