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Application Programming Interfaces (APIs)

APIs: Application Programming Interfaces

An API is one of the most important concepts in modern Software Development. The complexity behind building applications and software products often involves the integration of smaller and third-party apps. In other words, digital products like web and mobile apps combine other applications' functionalities to do the job more effectively. Complex apps like eCommerce, FinTech, Internet of Things (IoT), or Social Media platforms normally require tons of functionalities combining multiple apps. 

Software Developers use APIs' power to integrate multiple applications seamlessly. This way, they can build complex products with many features and functionalities way more easily. Even simple apps with a standard User Interface on the Front End use Back-End functionalities that need an API. You may not have realized it, but you interact with APIs using almost any app. That includes weather apps, Instagram, Tiktok, YouTube, Shopify, mobile games, and more. Understanding what an API is and how it works is way simpler than you might think. 

What is an API?

The term API stands for Application Programming Interface, and it basically defines how two apps exchange data. People describe it as a contract between two products involving specific protocols. 

There’s this classic analogy in a restaurant where the waiter works as an API, showing a menu to the customer. The menu (UI) displays all the available options to the customer, and the waiter (API) connects the order from the customer (user) to the kitchen (Back-End server). The waiter takes the finished meal to the customer. That example is key because the User Interface (UI) only shows what the customer can access. For security reasons, a user shouldn’t be able to access all the server’s data. Imagine a user being able to access other users’ records: that’s why robust security and protocols are so important with APIs.

What is an API Gateway?

Modern apps encompass tons of functionalities to provide a seamless User Experience (UX). As mentioned, software products involve many “smaller apps” for many purposes. That’s an oversimplified way of saying modern products normally use Microservice Software Architectures. But what does that have to do with an API Gateway? Having a Microservices Architecture translates to apps that receive many API calls from users. 

That can be particularly hard to manage, yet that’s where an API Gateway comes in. It acts as a central traffic controller to handle all the API requests from the client side of the app. An API Gateway is an entry point for a collection of Microservices, which helps boost performance and security, simplifying development. Teams can build an API Gateway from scratch, but it’s extremely difficult, or get one from a third party, like Kong, Amazon API Gateway, Azure API Management, Kong, and KrakenD

How do APIs work?

There’s really no need to make it look harder than it is. APIs work by defining a set of rules and protocols that determine how two applications interact with each other. The entities or apps involved in the process are normally a client and a server. The client makes a request to the server, and the latter gives back a response based on the API rules and protocols. The API shows the client what functions or methods to access through specific entry points. 

Going back to the restaurant example, you can think of entry points as the menu that shows the user only what’s available. Sometimes, actions require the client to provide specific credentials to grant access. APIs sometimes handle access requests with authentication and authorization by asking users to provide tokens, which are the permissions required for the requested entry point. 

Main Types of APIs

1. Web APIs

APIs come in different shapes and sizes, but roughly 99% of the time, when you hear someone saying API, they mean a web API. And guess what? It turns out that there are also various types of Web APIs, where the most common ones are REST APIs. You'll find them in big-name companies like Twitter, Paypal, Google Maps, Twilio, Instagram, and Stripe. RESTful means they comply with the architectural style of Representational State Transfer (REST). One of the most important aspects of REST is that it follows HTTP protocols for data transfer and security. However, there are more modern ways to work with APIs, such as GraphQL, gRPC, and tRPC

2. Library APIs 

Software Development Libraries like React.js, Ruby On Rails, Vue.js, and Angular.js meet the definition of an API. Yet, the way libraries work is pretty much the same as how APIs work. They give you access to pre-built functions and methods you can pull into your project following their conditions and constraints. As mentioned above, you probably won’t hear as many people talking about Software Development Libraries as APIs, yet this example helps you understand how they work. 

3. WebSocket APIs

There’s one more way of establishing a seamless connection between a client and a server. WebSockets are especially useful when your project requires instant updates, so developers normally use them in online games or apps with chatbots. They provide bidirectional and interactive communication, making them perfect for data streaming. That also explains why developers refer to them as a full-duplex connection. 

APIs in Software Development

APIs make users' and developers' lives simpler. For example, consider all the functionalities an eCommerce platform could have, such as pricing, reviews, sign-up, log-in, size/color selection, purchasing, order cancelation, and tracking shipments. Well, APIs allow developers to easily integrate all those features in a single app, providing a great UX to its users. As mentioned, APIs also allow completely external apps to exchange data. A perfect example could be the same eCommerce platform letting you log in using your Google account. 


APIs are key for anyone involved in Software Engineering, from QA testers and DevOps Engineers to Product Managers and Database Managers. Even business analysts may need to understand how data flows between systems depending on project requirements. Ultimately, API development is present in most large and scalable software platforms!