API: all about the application programming interface

API stands for Application Programming Interface. It allows software applications to communicate with each other. Although there are many protocols and technologies involved, the underlying goal of APIs is always the same: to allow one software application to communicate with another.

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APIs are sometimes described as web services. These run in the background whenever two applications interact. These make it easier for developers and improve the end-user experience.

To better understand, APIs allow developers to save time by leveraging a platform implementation to do the grunt work. This helps to Reduce the amount of code that developers need to create.. These codes also create more consistency between applications for the same platform.

Concretely, an API is a set of programming code that allows the transmission of data between a software product and another. This set also contains the modalities of this data exchange.

Each code set contains and is implemented by function calls. These are language instructions that instruct the software to perform particular actions and services. Function calls are described in the API documentation.

Why do developers use APIs?

Overall, they simplify and accelerate software development. Developers can add functionality from other vendors to existing solutions or create new applications using third-party services.

In all of these cases, developers do not have to deal with the source code when using this system. They simply connect their software to another. In other words, the codes serve as an abstraction layer between two systems, hiding the complexity and details of their operation.

APIs make developers’ lives easier

Suppose a developer wants to develop an application for an iPhone. Apple’s iOS operating system provides a large number of APIs, as do all other operating systems, to make his job easier.

If the developer wants to integrate a web browser to display one or more web pages for example, he does not need to program his own web browser from scratch for this one application.

And this applies to all platforms. For a developer who wants to create a dialog on Windows or another who wants to integrate fingerprint authentication support on Android, the principle remains the same.

Resource access control

All about the application programming interface

APIs are also used to control access to hardware devices. They are also used for software functions that require access authorization.

Other reasons to use an API include

The API allows two different software to communicate and exchange data between them, but not only. It also helps to:

  • integrate more efficiently the content of any site or application
  • access application components
  • automatically publish generated content
  • allow the user or a company to personalize the content and services they use the most
  • anticipate changes in software that are constantly evolving.

The different types of API

Code sets are generally classified into 4 categories: private, partner, public and composite.

Private APIs

This category is designed to enhance solutions and services within an organization. Internal developers or contractors can use them to integrate with an organization’s IT systems or applications. They also use them to create new systems or applications for customers by leveraging existing systems.

Even if the applications are publicly available, the interface itself remains available only to those who work directly with the editor. The private strategy allows a company to fully control its use.

API partners

API: All about the application programming interface

So-called partner APIs are openly promoted, but shared with business partners who have signed an agreement with the publisher. Partner APIs are commonly used for software integration between two parties.

A company that grants partners access to data or capabilities can monitor how exposed digital assets are used. It ensures that third-party solutions using their APIs improve the user experience and Maintain the company’s identity in their applications.

Public APIs

These APIs are available to all third party developers. There are two types: open (free) and commercial. The first category suggests that all features are public and can be used without restrictive conditions.

A developer can use the public API to create an application without explicit approval from the publisher or licensing fees. Open is available for free, this category can be used freely to create and then test applications.

For commercial public APIs, developers pay a subscription fee or the use on a pay-per-use basis. Publishers often offer free trials so that users can evaluate them before purchasing a subscription.

Composite API

This type of API combines different data and service APIs.

Categories by use cases

All about the application programming interface

APIs can also be classified according to the systems they are designed for.

Database API

Database APIs enable communication between an application and a database management system. Developers work with databases by writing queries to access data, modify tables, etc.

Operating System APIs

This group defines how applications use operating system resources and services. Each operating system has its own set of APIs.

Remote APIs

Remote APIs define interaction standards for applications running on different machines. In other words, a software product accesses resources located outside the device that requests them.

Since two remote applications are connected over a communication network, especially the Internet, most remote APIs are written based on Web standards.


This API class is the most common one. Web APIs provide machine-readable data and functionality transfer between Web systems that represent the client-server architecture. These APIs primarily deliver web application requests and responses from servers using the Hypertext Transfer Protocol (HTTP).

Developers can use Web APIs to extend the functionality of their applications or sites. Most companies use multiple APIs to connect applications and share information. Some end up needing a management tool to help them control, distribute and analyze different systems in use.

Authentication and keys

Generally, an API does two things: support communication between tools and control access to resources. The way APIs control access to resources is through authentication (identifying the user) and the authorization (determining what the user is allowed to access).

The common form of authentication uses username and password. With APIs, a API key. This is an identifier embedded in the API calls that identifies the user and determines what they are allowed to access from the server.

The documentation

All about the application programming interface

No matter how many opportunities for creating or extending software products the API offers, it would still be an unusable piece of code if developers didn’t understand how to use it.

Documentation is a reference manual containing all the necessary information about the API. Good documentation includes, among other things:

  • a quick start guide
  • authentication information
  • explanations for each call (request)
  • examples of each request and return with a description of the answer, error messages, …
  • code examples for popular programming languages like JavaScript, Python or PHP
  • tutorials
  • SDK examples (if SDKs are available) illustrating how to access the resource, etc.

Documentation typically consists of two columns: human and machine. The human column contains API descriptions. The machine column has a console for making calls. This part also contains information that is of interest to the clients as well as the servers during testing.

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