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What is an API? 

Have you heard about APIs but don’t know what exactly they are? If you have done any coding, you’ve probably used one already. API stands for an application programming interface.

Why do you need an interface?

Interfaces talk to each other and hide the complexities of the software from users. Think of your computer’s desktop. Instead of a complex terminal, your computer’s operating system gives you a screen with icons. We call this interface a GUI – Graphical User Interface. So when you click on a file to open it, you don’t have to know how the OS does it. 

Difference between user interfaces and APIs

Most software gives you a user interface (UI) so you can interact with it. UI’s are friendlier ways to interact with the software than pure code. In a user interface, you’ll see icons and sets of menus that you can select from. 

Application programming interfaces (APIs) do the same thing for developers. So when you build software for other developers to use, you need to give them an API.

APIs can reduce your workload significantly. Building large applications is nearly impossible if developers have to code everything from scratch each time.

What are web APIs?

Web APIs are the most common type of APIs.

While a Java API allows two applications on the same machine to talk with each other, web APIs let two applications on different machines communicate. 

Web APIs are usually built on the client-server model. The client sends requests and receives messages from the API hosted on the server.

There are several types of web APIs. The most popular and easiest to use are RESTful APIs (also known as REST APIs).

Web APIs reside on different machines. So they are exposed as URLs called endpoints. Different functions will have different URLs. You have to send an HTTP request to get an output from a web API. If you want to pass arguments, you have to attach them to the URL.

You send HTTP requests whenever you load a web page. For instance, you send a GET HTTP request to the URL of this blog page to view it.

Let’s understand web APIs with an example. Here is a REST API that can be used for math operations. https://api.mathjs.org/

If you want to get the result of 2×4 you have to send the following request:


You will get 8 as the output. 

Send this URL if you want to find the square root of 9:


You will get 9.

APIs are used for sending data

Are APIs only used to get functionality with some complex calculation? No. APIs are used to share data as well.

For example, the IMDb PI is an API for retrieving information about movies.

There are many advantages of using APIs as a way to share data.

Usually, this large amount of data is stored in databases. Providing access to databases for sharing data is risky. Thus APIs work as a middle layer between the database and the users who need data. 

You can create much more complex access privileges for an API than in a database management system. You can decide exactly who is going to access which data. With the database, you have to deal with the options the database system offers.

Furthermore, it’s easier to implement security for a web API than for a database.

You can create several pricing options based on the number of available requests and data. It will be more affordable than buying the whole dataset. Thus you can increase your customer base.

Why should you use APIs?

As you can see, APIs can greatly reduce your workload. You don’t have to code something that someone has already built. However, that’s not the only advantage of using APIs.

You can distribute the load on your server using APIs. Suppose you have built your whole application as one core. Then your server containing the application has to deal with many things. It must handle all the requests, processes, calculations and storage alone. You can reduce the workload of your server by using APIs.

Furthermore, APIs simplify the maintenance of your code. You will have fewer files that are easy to maintain.

Usually, good APIs are well-built. They increase your application’s performance and security compared to writing all the code yourself.

Moreover, your application will have fewer bugs as you will have less code.

APIs help to scale apps easily. You can simply integrate an API if you want to add new functionality to your application. 

What are APIs used for?

Now you know the importance of APIs, you may want to know how you can use APIs. There are APIs for building any type of application. You will find APIs for all different types of applications.

For example, here is an API about basketball: https://rapidapi.com/api-sports/api/api-basketball/

It provides you with information about different leagues, games, seasons, and players.

Here is a finance API: https://rapidapi.com/category/Finance

And a flight data API: https://rapidapi.com/collection/flight-data-apis

APIs like the above contain a lot of data. So it’s impossible to gather such data by yourself.

Even companies like Facebook, Twitter, and Google use APIs. You use their APIs when you integrate services from their products.

APIs can be completely free or paid. There are some APIs that provide only certain features for free to attract customers.

Why should you build your own APIs?

Now you understand why you should use APIs built by others. But do you know how to build APIs by yourself? Yes, nowadays, most relatively large applications use their own APIs.

Think of a large e-commerce application. We can break the application into three services called products, sales, and admin. Then you can expose them to each other through APIs.

For example, the product service will include all the functions related to products. Its API will have endpoints to access the following functionalities.

  • How to add a product
  • Finding a product with a certain id
  • Finding a list of products of a certain category
  • Find all products
  • Delete a product
  • Update a product

Here customers use a web UI to give commands. The web UI uses APIs to provide the functionality you need.

The API of the sales service will include endpoints to do the following things.

  • Make an order
  • Find a discount for a certain product
  • Find monthly revenue

Suppose the admin wants to find the monthly value. The good thing is that he will only interact with the sales API. So it doesn’t affect the performance of customers who view products.

When it comes to large web applications, there are many users doing different things. Think of a web application for a large university. There are so many people doing things that are unrelated to each other.

  • Students enrolling on a course
  • The sales team analyzing the revenue
  • Marketing teams sending emails

There are advantages to breaking a large application into a set of services. Performance is only one of them. Services are much easier to develop, test, debug and deploy as they are small. It’s also easier to break developer teams into different services.

This concept led to the emergence of popular web development architecture called microservices. Microservices means we build web applications as a set of smaller independent services. Microservices use APIs to communicate between these services. So it’s important that you know how to build APIs if you want to work for a big tech firm.

How to develop an API

Developing an API is like making a web application. You use the same tech stacks and it’s actually easier because you don’t deal with user interfaces. However, there are important decisions to make when building APIs.

First, decide who your intended audience is. APIs provide specific functionality. You can’t do everything in an API. If it’s a weather API, it will include weather data. If it’s a movie API, it will have movie data.

Then decide on the API type. Currently, the most popular API type is RESTful APIs. They are easier to develop and consume.

Next, decide what API responses you send for requests coming to each endpoint.

After that comes the usability of the API. The endpoints you provide determine the usability of an API.

Many applications use APIs. So you have to ensure the API can handle many requests. Also, try to avoid any downtime.

You also have to think about security. Only the authorized users should have access to a given endpoint.


API is an architecture for two software applications to communicate with each other. There are APIs for basically any type of application. As a developer, you’ll use APIs built by others and sometimes you’ll build APIs by yourself. Next time, your target should be trying to build an API yourself.