In programming generally, the term API, short for Application Programming Interface, refers to a part of a computer program designed to be used or manipulated by another program, as opposed to an interface designed to be used or manipulated by a human. Computer programs frequently need to communicate amongst themselves or with the underlying operating system, and APIs are one way they do it. In this tutorial, however, we’ll be using the term API to refer specifically to web APIs.
If you’ve heard the term API before, chances are it’s been used not to refer to APIs in general, but instead to a specific kind of API, the web API. A web API allows for information or functionality to be manipulated by other programs via the internet. For example, with Twitter’s web API, you can write a program in a language like Python or Javascript that can perform tasks such as favoriting tweets or collecting tweet metadata.
When using or building APIs, you will encounter these terms frequently:
HTTP (Hypertext Transfer Protocol) is the primary means of communicating data on the web. HTTP implements a number of “methods,” which tell which direction data is moving and what should happen to it. The two most common are GET, which pulls data from a server, and POST, which pushes new data to a server.
URL (Uniform Resource Locator) - An address for a resource on the web, such
as https://programminghistorian.org/about. A URL consists of a protocol (http://), domain (programminghistorian.org), and optional path (/about). A URL describes the location of a specific resource, such as a web page. When reading about APIs, you may see the terms URL, request, URI, or endpoint used to describe adjacent ideas. This tutorial will prefer the terms URL and request to avoid complication. You can follow a URL or make a GET request in your browser, so you won’t need any special software to make requests in this tutorial.
REST (REpresentational State Transfer) is a philosophy that describes some best practices for implementing APIs. APIs designed with some or all of these principles in mind are called REST APIs.