In a world where everything is connected, APIs are the glue that holds it all together. You might not realize it, but you use APIs every day. 

From checking the weather on your phone to ordering food online, APIs are behind the scenes making it all possible. But what exactly is an API? 

In this article, we’ll explore what APIs are, how they work, different types of APIs, and why they are essential to the functioning of many modern-day applications. 

What is an API?

An API, or Application Programming Interface, is a set of rules and protocols that allow different software programs to communicate with each other. It’s like a messenger that relays information and instructions between two different applications.

For example, you’re ordering food at a restaurant. You look at the menu, choose what you want to eat, and then tell the waiter your order. The waiter then takes your order to the kitchen, where the chef prepares your meal. When it’s ready, the waiter brings your food back to you.

In this scenario, the menu is like an API. It provides you with a list of available options and helps you select. The waiter is like the API itself, taking your order (or request) and relaying it to the kitchen (or the application you’re interacting with). The chef is like the application that receives the request, processes it, and returns a response.

APIs can be used to perform a wide variety of tasks. They can retrieve data from a remote server, send data to a remote server, initiate a process on a remote system, and more. In other words, they allow different applications to work together and exchange information and functionality.

For example, you’re making a mobile app that shows the latest weather information. You could use an API provided by a weather service to retrieve the current weather conditions and forecast data for a specific location. Your app would send a request to the weather service API, which would then return the requested data. Your app could then display that data to the user.

APIs come in many different types and formats, but they all serve the same fundamental purpose: to enable different applications to communicate and work together. They’re an essential part of modern software development and play a crucial role in allowing the integration of diverse systems and services.

How Does an API Work?

API works by allowing one software program to request information or functionality from another software program or service. The API acts as an intermediary, translating the request from the first application into a format the second application can understand and then sending the request to the second application.

To use an API, you typically send an API request/call to the API server with specific parameters or data. The API server then processes your request, retrieves the relevant data, and sends it back to you in a format you can use in your software program or application.

APIs often use a standard protocol, such as HTTP (Hypertext Transfer Protocol), which is the same protocol used to browse the web. HTTP allows software applications to communicate over the internet and exchange data in a standardized format.

APIs are designed to be language and platform-independent, meaning they can be used by any application that can make HTTP requests. This makes APIs incredibly versatile and helpful in building complex systems with many applications.

Here are the key components of an API:

• API Call/Request – An API call is a request a software application sends to an API to perform a specific action or retrieve information. A client application initiates an API call, which sends a request to the API using a defined protocol, such as HTTP or TCP/IP. The API then processes the request and responds to the client.

• API Server – The API server is the application that hosts the API. It receives the API request, processes it, and returns a response.

• API Response – The API server sends the API response back to your application. The response contains the data or service you requested in a structured format, such as JSON.

• API Endpoint – An API endpoint is a URL you use to call the API server. Endpoints are typically designed to perform specific functions, such as retrieving data or performing a particular action.

• API Authentication – Some APIs require authentication before you can use them. Authentication typically involves obtaining an API key or token from the API provider, which is used to authenticate your requests to the API server.

• API Documentation – APIs typically come with documentation that explains how to use the API and what requests and responses are available. Documentation can include information on authentication, API endpoints, parameters, and response formats.

Representational State Transfer (REST) and Simple Object Access Protocol (SOAP), which specify a standard communication protocol definition for a message exchange based on Extensible Markup Language (XML), are the two most popular API architectures. 

Compared to REST, SOAP requires fewer low-level infrastructure-related codes. Conversely, REST APIs are simpler to implement, integrate with websites and services, and are easier to scale and redeploy. Nowadays, REST APIs are most often used, especially for web applications.

For example, you have a mobile app that lets users search for and view information about books. You could use an API provided by a book database service, like Goodreads or Google Books.

When a user types in a search query in your app, your app sends a request to the book database API with the search query as a parameter. The book database API server then processes your request and retrieves information about the books that match the search query.

The API server then responds to your app containing information about the matching books in a structured format, such as JSON. Your app can then use this data to display the search results to the user.

This way, APIs enable different software applications to work together and exchange information, making it possible to build complex, integrated systems to perform various tasks.

Types of API

There are different APIs, each with unique features and use cases.

1. Public APIs: Public APIs are available to anyone and are often provided by companies or organizations to make their services available to third-party developers. These APIs are accessible over the internet and are generally free to use. Public APIs often have usage limits or restrictions in place to prevent overuse or abuse. Examples of public APIs include the Twitter API, Google Maps API, and OpenWeatherMap API.

2. Private APIs: Private APIs are not publicly available and are only accessible within a specific organization or company. Private APIs are often used for internal communication between different applications or systems. Private APIs are usually more secure than public APIs since access is restricted to authorized users only. Examples of private APIs include those used by companies like Amazon or Google for their internal operations.

3. Partner APIs: Partner APIs are accessible only to a select group of users or developers who the API provider has granted permission. Partner APIs provide more advanced functionality than public APIs and may require a partnership agreement or some kind of contract to access. Examples of partner APIs include the Facebook Marketing API and the Salesforce API.

APIs can also be classified based on their implementation, which can be local, web-based, or remote.

• Local APIs: Local APIs are installed on a user’s device, such as a mobile phone or computer. These APIs are used to access device-specific features like the camera, microphone, or GPS. Local APIs are used to develop native applications for mobile devices or desktop computers.

• Web APIs: Web APIs are used to access web-based services like social media or online banking. These APIs are accessible over the internet and are often used to develop web applications. Examples of web APIs include the Facebook Graph API and the PayPal API.

• Remote APIs: Remote APIs are used to access services hosted on a remote server. By using a communication network, remote APIs can interact with resources outside the computer, making the request. Web APIs fall under this broader category, which also covers other types of APIs. While many remote APIs are, they are not required to be built using web standards. Examples of remote APIs include the Java Remote Method Invocation API and the Java Database Connectivity API.

History of API

APIs (Application Programming Interfaces) have been around for a long time, even before the term was officially coined. In the 1940s, British computer scientists Maurice Wilkes and David Wheeler created a modular software library for EDSAC, an early computer. They stored subroutines on punched paper tape and cataloged them to instruct programmers on how to use them, similar to how modern APIs provide documentation for developers.

The term “application program interface” (API) was first used in a 1968 paper on remote computer graphics, referring to the interaction between an application and the computer system. 

APIs became a part of the ANSI/SPARC framework for database management systems, treating application programming interfaces separately from other interfaces like query interfaces. 

By the 1990s, APIs were defined as a set of services available to a programmer for performing certain tasks.

As computer networks became more common in the 1970s and 1980s, programmers wanted to call libraries located on computers elsewhere, leading to the development of remote procedure calls and web APIs. 

The Java language supported remote procedure calls, while standards like CORBA, COM, and DCOM competed to become the most common way to expose API services.

In the 2000s, web APIs and Representational state transfer (REST) gained widespread commercial adoption, becoming the most common type of API. 

Roy Fielding’s dissertation on Architectural Styles and the Design of Network-based Software Architectures in 2000 introduced REST and described the idea of a “network-based Application Programming Interface” that Fielding contrasted with traditional “library-based” APIs. XML and JSON became popular data formats for web APIs.

Today, APIs have become a broad term describing much of the communication on the internet, particularly for exchanging data of all kinds. 

While proprietary interfaces and agents are more widespread than open ones, the idea of the API as a data interface has taken hold. 

With the development of emerging technologies like the Internet of Things (IoT), APIs will continue to play an essential role in allowing systems to connect and communicate.