The key purpose of a software development kit (SDK) is to provide developers with a set of tools, libraries, and documentation for creating software applications for specific platforms or frameworks. SDKs enable developers to streamline the development process by offering pre-built functionalities, code samples, and application programming interfaces (APIs) that simplify integration with other services. By utilizing SDKs, developers can enhance productivity and reduce time-to-market by avoiding the need to build components from scratch. Overall, SDKs play a crucial role in fostering innovation and supporting the development of high-quality applications.