What is an API?

John Spacey, updated on November 18, 2016

An API, or application programming interface, is a set of services that code offers to the outside world. Code includes inner details that are intended to be hidden from the world in order to make things simpler. An API offers services using a well defined contract that specifies required parameters and results. Generally speaking, all code that is intended to be reused is wrapped in an API.

Example

APIs are similar to user interfaces but for code. For example, a user interface might let a customer pay a bill by providing their authentication details, entering an amount, selecting a bill and pushing a few buttons. An API could be constructed with the same functionality. The API might require authentication and then allow a bill to be paid by providing data such as an amount and a billing account number.

Complexity Hiding

APIs allow complexity to be hidden so that coders don't need to understand every little detail of a program. If a coder needs to encrypt some data, they probably don't want to deal with the complexity of encryption algorithms. As such, an encryption API may provide a service that allows a programmer to encrypt something by passing in parameters such as a key and data to be encrypted.

Overview: API
Type	Coding
Definition	A service that code offers via a well defined contract that specifies parameters and results.
Value	Hiding the complexity of code behind an easy to use interface.
Also Known As	Application programming interface
Related Concepts	Coding Algorithms Complexity Hiding Deep Magic