What is an API?

APIs are mechanisms that enable two software components to communicate with each other using a set of definitions and protocols. For example, the weather bureau’s software system contains daily weather data. The weather app on your phone “talks” to this system via APIs and shows you daily weather updates on your phone.

An API, or application programming interface, is a set of defined rules that enable different applications to communicate with each other. It acts as an intermediary layer that processes data transfers between systems, letting companies open their application data and functionality to external third-party developers, business partners, and internal departments within their companies.

The definitions and protocols within an API help businesses connect the many different applications they use in day-to-day operations, which saves employees time and breaks down silos that hinder collaboration and innovation. For developers, API documentation provides the interface for communication between applications, simplifying application integration.

How An API Works

A simple way to understand how APIs work is to look at a common example—third-party payment processing. When a user purchases a product on an ecommerce site, they may be prompted to “Pay with PayPal” or another type of third-party system. This function relies on APIs to make the connection.

When the buyer clicks the payment button, an API calls to retrieve information—also known as a request. This request is processed from an application to the web server via the API’s Uniform Resource Identifier (URI) and includes a request verb, headers, and sometimes, a request body.
After receiving a valid request from the product webpage, the API makes a call to the external program or web server, in this case, the third-party payment system.
The server sends a response to the API with the requested information.
The API transfers the data to the initial requesting application, here the product website.

While the data transfer will differ depending on the web service being used, the requests and responses all happen through an API. There is no visibility on the user interface, meaning APIs exchange data within the computer or application, and appear to the user as a seamless connection.

Types of APIs

Today most APIs are web APIs that expose an application’s data and functionality over the internet. Here are the four main types of web API:

Open APIs are open-source application programming interfaces you can access with the HTTP protocol. Also known as public APIs, they have defined API endpoints and request and response formats.
Partner APIs connect strategic business partners. Typically, developers access these APIs in self-service mode through a public API developer portal. Still, they need to complete an onboarding process and get login credentials to access partner APIs.
Internal APIs remain hidden from external users. These private APIs aren’t available for users outside of the company and are instead intended to improve productivity and communication across different internal development teams.
Composite APIs combine multiple data or service APIs. They allow programmers to access several endpoints in a single call. Composite APIs are useful in micro services architecture where performing a single task may require information from several sources.

APIs vs. Web Services

A web service is a software component that can be accessed and facilitates data transfers via a web address. Because a web service exposes an application’s data and functionality to other applications, in effect, every web service is an API. However, not every API is a web service.

APIs are any software component that serves as an intermediary between two disconnected applications. While web services also connect applications, they require a network to do so. Where some APIs are open source, web services are typically private and only approved partners may access them.

How to use an API?

The steps to implement a new API include:

Obtaining an API key. This is done by creating a verified account with the API provider.
Set up an HTTP API client. This tool allows you to structure API requests easily using the API keys received.
If you don’t have an API client, you can try to structure the request yourself in your browser by referring to the API documentation.
Once you are comfortable with the new API syntax, you can start using it in your code and contact ElmMac for any assistance.