What is API?

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By Sina Nasiri

If you’ve been associated with IT, especially software and web development, you must have come across the word “API” more than often. It is a critical component that is used in nearly every application, website, framework, etc. to interact with one another.

Since software or other elements doesn’t require a graphical user interface for communication, the only way for them to exchange data and other stuff is machine-readable interfaces known as APIs. Let’s learn about API (Application Program Interface) in detail along with its working, types, implementation, and other associated information, which will make it easier for you to work with them.

What is an API?

API or Application Programming Interface is a set of codes that allows the transfer of data and various information among different software and/or websites. Helping web-based systems to communicate with each other, APIs also enable them to receive data from various third-party resources. For example, sending instant messages through social media platforms is possible through API. Have a look at the following points for better understanding:

  • API requests are sent for delivering specific pieces of information.
  • It helps in incorporating components on different platforms for smooth redirections. For example, adding “Share on Facebook” and “Share on Twitter” buttons on websites.

In simple words, if an application wants to fetch any specific information from any other application, it will call its API, if available. Application on the other side will return the requested functionality or data through the similar interface which they’ve been using for communicating.

  1. Technical specifications were done in the form of requests for defining the exchange of the data among software and processing them via protocols
  2. The software interface for representing specifications

Implementation of every API is done through function calls that are simple statements for requesting software to process the desired operation.

Types of APIs

1. Private APIs

They’re developed and designed for usage within an organization. They’re built with the main focus for integrating various system software and applications of the company or creating new systems for existing applications. Even if the applications are available to everyone, its Application Program Interface would still be limited for the members of the organization and its API publisher. Also, private APIs enable companies to easily manage and control API usage.


They’re designed to be hidden from external users and allows various teams within an organization to make use of each other’s tools, data, and programs. They come with better conventional integration techniques, along with security and access control and a standard interface for bridging multiple services.

2. Partner APIs

They’re distributed openly but to a restricted audience that can also be outside of a specific organization. It is typically shared with business partners who agree on documents and terms of use assigned by the provider. It is majorly used in the case of software integration between two parties (Shopify stores and eBay, Walmart, etc.). The company that provides the APIs enjoys a lot of benefits from extra revenue streams. In addition, tracking and monitoring the usage of the products or software by third-party companies can also be performed.

3. Composite APIs

With the help of Composite APIs, developers are enabled to enter the endpoints in one call. An API can have multiple endpoints, data sources, and services that are extremely beneficial for microservice architecture into which users have required information from different places to achieve the desired goal. Using composite APIs can reduce server load and improve application performance, as one call can return all the data a user needs.

4. Public APIs

A public API is open for the usage of any third-party business. Often referred to as developer-facing or external APIs, public APIs can be of good use for businesses as they can help to increase brand awareness and also make a good amount of money if used tactically. Generally, Public APIs are categorized into the following two types:

  1. Open API
  2. Commercial API

The Open APIs allow anyone to utilize the features without being bound by any terms and conditions or charges. For example, an application that uses the API without requesting any approval or agreeing on any document for the provider.

Whereas, Commercial APIs are available on a per-subscription basis or take charges for using them every time. However, majorly all the API suppliers offer free trials for users to evaluate the functionalities before the actual payment of the subscriptions.

How to Build an API?

Any developer who is aware of server-side web application programming and routing will be able to create an API that can be used for various purposes. They should also have the knowledge and hands-on experience working with back-end or server-side web application frameworks such as Java Spark, Express.js, ASP.net for C#, Ruby on Rails, and so on. Following are some of the prerequisites for building an API:

  • A database for storing all of the information. It can be any existing database you’re utilizing, such as MySQL or Postgres or it can be BaaS (backend as a service) such as Firebase.
  • A virtual private server (VPS) that can be used over the internet and have various applications running over it.

Connecting API with Applications

By including various APIs in your applications, you can enhance their functionalities to the next level. You can make use of APIs to add features such as maps, weather forecasting, social share buttons, and tons of various other things to your websites and web apps.

Here are some key things that you need to do to connect third-party APIs with your web-based systems:

  • Research for an API with a dedicated feature that you want to add to your application. Check everything and go through the reviews along with terms and conditions to ensure that the API is safe for your application and takes care of privacy.
  • Check the documentation for knowing whether the API will work for you or not. Check security concerns and also evaluate the value that it will add to your application.
  • Dig deeper to learn about its dynamics. You can opt to choose the ‘Postman tool’ that will help in knowing about various aspects of working with the selected API smoothly. You’ll also be able to test the APIs by simply sending test requests and checking the data you received.
  • After testing the API with the help of appropriate tools, you can proceed further to write code for integrating the API with your application. During the integration process, you may need to make API calls several times to check if your application is receiving the right set of data through the API.

Classification of APIs on the Basis of Use Cases

1. Database APIs

Database APIs bridges any application or software with its respective database management system for feasible communication. Developers make use of query language for accessing the data, changing tables, etc.

2. Operating systems APIs

These APIs align with how a specific app will utilize the resources using an operating system. Every operating system comes with a set of APIs, for example, kernel–user-space API and kernel internal API. Apple also offers API for macOS and iOS.

3. Remote APIs

This application program interface is used for maintaining communication between applications that often toggle between various machines. In simple words, these applications utilize resources that are situated outside the device that requests them. The remote APIs are written considering internet standards because remotely-located applications typically connect over the internet. For example, Java Database Connectivity API and Java Remote Method Invocation API.

4. Web APIs

It is the most common and widely-used API as compared to others. They offer data that can be read by machines and features through which data transmission among web-based systems with client-server architecture is done. They are majorly used for delivering requests from web apps and reply through servers via HTTP (HyperText Translate Protocol).

They’re also utilized for including additional features to an application or a website. For example, Pinterest API offers a set of web APIs for including its data on any website with boards or Pins.

The Modern API

For the past few years, APIs are known majorly for making smooth connection interfaces for applications. But with the advancements over time, the modern API has adopted various unique features that make them more valuable and useful:

  • The Modern APIs follow the industry standards for HTTP that makes them more developer-friendly with improved accessibility and broader scope.
  • They’re now considered more as a product rather than just a code and can also be utilized for commercial purposes. They can be developed for narrow audiences as well and come with proper documentation along with less maintenance.
  • Since they’ve seen a lot of modifications and offer additional functionalities, they are backed by advanced security and governance with improved monitoring and managed for performance and scale.
  • Modern APIs come with their own software development lifecycles to maintain the design, tests, management, and updating versions.


APIs play an extremely crucial role in proceeding nearly every communication among software and applications. It not only helps in developing better applications but also assists businesses to collaborate effectively. These machine-readable interfaces efficiently process the delivery of data and functionalities that work under the hood and offer unbreakable connectivity. Following are some of the most important key takeaways regarding APIs:

  • Helps developers to get instantaneous analytics data.
  • They’re an efficient way to get information or add functionality provided by a third party.

Therefore, selecting APIs that work or add value to the business and understanding how to make the most out of them are key tasks for business owners and developers.

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