Eric Kleppen | Jan 06, 2023

An API, or an application programming interface, acts as an intermediary between software and allows two applications to communicate and work with one another. APIs are critical to how software operates and are used by software engineers to enable the instantaneous sharing of data to provide seamless user experiences.


How Do APIs Work?

APIs function by passing information from a service provider to an application via an API endpoint. They are often a key component to interoperability in software development, often facilitating the transfer of data via request and response. 

APIs work by delivering a request to a system and sending the system’s response back to whatever made the request. This process allows for shared functionality allowing between one application and another.

A critical component of an API, known as the API endpoint, provides a specification by which the applications can communicate, thereby decoupling the consuming application from the infrastructure providing that API endpoint. As long as what the delivering requester follows the endpoint’s specifications, changes to the service provider’s infrastructure won’t alter how API-reliant applications receive data. This process facilitates flexibility between separate infrastructures or applications.

What Is an API? | Video: MuleSoft Videos


API Examples

A common example of APIs in use are applications accessed through a mobile device, such as a weather app, social media app, finance app or GPS app.

Applications, mobile or otherwise, work by connecting to the internet and sending data to a server. Upon receiving that data, the server will interpret and complete all possible actions requested by the application and return it to the source. That application will then receive, process and display the data  to the user in the way it is programmed. 

Let’s look at the weather app example. When a user opens the application, the API will send a request to the database to retrieve the current forecast based on the device’s location, date and time of day (which are also pulled with separate APIs). The database will receive that request, locate the necessary data and return it to the weather app, which will present it in the form of temperature and conditional readings. Many APIs function simultaneously within an application to deliver instantaneous results.

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API and a REST API: What’s the Difference?

REST APIs are a subset of APIs that provide an architecture for API development. REST APIs facilitate faster build times and better adaptability. All APIs aren’t REST APIs, but all REST APIs are APIs. REST APIs are simply APIs constructed using REST architecture (representational state transfer).

APIs are considered RESTful only when requests are managed through HTTP. REST APIs often require headers and parameters to be passed in the API call as well. Common types of API requests include GET, POST, DELETE and PUT.

Other characteristics of the RESTful architecture include a stateless client-server connection (so each request is unconnected and secure), cacheable data and a uniform interface for maintaining a standard in how information is passed.

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