The term “SDK” (which stands for “Software Development Kit”) lacks concrete meaning. The common understanding is that an SDK differs from an API as it provides both program interfaces and tools to work with them. This definition is hardly satisfactory as today any technology is likely to be provided with a bundled toolset.However, there is a very specific narrow definition of an SDK: it is a client library that provides a high-level interface (usually a native one) to some underlying platform (such as a client-server API). Most often, we talk about libraries for mobile OSes or Web browsers that work on top of a general-purpose HTTP API.