API and SDK

Two terms in software development that are often confused are API and SDK. API stands for “Application Programming Interface” and refers to programming instructions and standards for accessing a web tool or database. For example, a software company will often release its API publicly or privately to other software developers so that they can design products powered by its service. An API can be packaged in an SDK, or “Software Development Kit“.

An SDK is typically a set of software development tools that allows the creation of apps for a specific platform. SDKs can include one or more APIs along with programming tools and documentation. Take the SDK for Java, which contains an API as well as compilers, runtimes and other miscellaneous tools.

An API is a set of libraries that make up the core language that you can work with out of the box, whereas an SDK is a development kit that facilitates usages of an API. Conceptually both are a way for your program to interface with and control the resources provided by another piece of software. That software could be a web service, an end-user app, an OS service or daemon, or a kernel device driver.

So, the real difference is that an API is no more or less than an interface to a service, while an SDK is a set of tools or components for a specific purpose. In fact, an SDK presents you with an API to interface with, but you might use an API without having the underlying components, for example when the API is provided through a web service.