What Is an API and an SDK?

An API (Application Programming Interface) is a defined way for one piece of software to talk to another — usually over HTTP for web and mobile products. Your app asks the API for data or actions; the API responds according to a contract.

An SDK (Software Development Kit) is a packaged set of tools, libraries, and helpers that make using an API (or platform) easier in a specific language or environment. The API is the door; the SDK is a well-labeled keyring.