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What is an API

Application Programming Interface (API) is a software interface that enables two applications to communicate without requiring a user to get involved. It is a group of computer programs and operations. It is a software code that may be viewed or performed, enabling data exchange and communication between two software programs.

Command-line tools, corporate code, microservices, and cloud-native architectures are all examples of where the concept of API is used. It is an interface that programmatically interacts with software resources or components that are not part of the developer's code. It is the area of a software component that other components can access. Unless you write every line of code from scratch, you will interact with external software components, and each of these has an API. Even if you write all of your code from scratch, a well-designed application should include internal APIs to help organize the code and make its parts more reusable.

Whether creating basic applications or the most complex designs and architectural considerations, the API is essential. It allows products and services to interact without needing to understand how those products and services are put into practice.

What is an API

How does API work?

An API is a set of rules that describe how computers or programs interact with one another. (Typically, an API specification will contain documentation of these criteria.) APIs are a middle layer that handles data transfer between systems, sitting between an application and the web server.

An API operates as follows:

A client application launches an API request called an API call to obtain information. This request, which includes a request verb, headers, and occasionally a request body from an application to the web server, is handled by the API's Uniform Resource Identifier (URI).

  • The API contacts the external program or web server after receiving a legitimate request.
  • The API receives a response from the server containing the data requested.
  • The data is sent from the API to the initial application that requested it.

While the data transport method varies based on the web service utilized, the entire request and response procedure is handled by an API. An API gives computers, or other programs access to the data and functionality of an application, whereas a graphical user interface only gives that access to humans.

Since API endpoints separate the application that uses the service from the infrastructure that supplies it, security is inherently provided by APIs as a result of their role as a mediator. Access can be restricted by an API gateway to reduce security threats, and authorization credentials are frequently included in API calls to limit the possibility of server intrusions. The exchange of the data is further made secure by the use of HTTP headers, cookies, or query string parameters.

What is an API

Take, for instance, a payment processing service's API. On the front end of an application for an online store, customers can submit their card details. The payment processor does not need access to the user's bank account because the API creates a unique token for this transaction and includes it in the API call to the server. The risk of hacking is, therefore, better protected as a result.

Why would we need an API?

An application programming interface can help you manage current tools or create new ones while simplifying the process. Here are a few reasons for using API:

  • Easier innovation: Businesses have more freedom thanks to APIs since they can connect with new business partners, offer new services to their current customers, and eventually access new markets that can generate sizable returns and hasten the digital transformation.
  • Ease of maintenance: The API is used to establish a gateway between two systems. Each system must make internal modifications to make sure the API is not affected. In this way, any future code changes made by one side won't have an impact on the other.
  • Flexibility: API-focused platforms are so effective at importing and exporting data that they do not require other software management systems to keep data records. Because of this, businesses may now improve the functionality of their systems, giving their IT budgets more flexibility.
  • Improved collaboration: APIs make integration possible, allowing these platforms and apps to connect without interruption. Businesses may streamline procedures and enhance teamwork through this integration. Without APIs, many businesses would experience information silos and a lack of connectedness that would impair productivity and performance.
  • Integration: APIs are used to connect new apps to already installed software. As a result of not having to write every functionality from scratch, development time is sped up. To make use of preexisting code, use APIs.
  • Automation: Application Programming Interfaces can automate some time-consuming, repetitive business operations that employees would otherwise have handled manually. This can decrease the possibility of human error in crucial business operations and free up an employee's precious time so they can work on other, more intellectually interesting organizational responsibilities.
  • Personalization: Businesses can utilize APIs to customize and personalize their products and services. Consumer information can be automatically imported into unique applications and content using API tools and pre-stored visitor data. 80% of customers are more likely to purchase a good or service from a business that offers customized experiences.

Features of API

API features can include:

  • Authentication: Authentication is verifying who users are and ensuring they are authorized to access the data or resources they request.
  • Authorization: Authorization ensures that users are only allowed to access data or resources that they are allowed to access.
  • Rate Limiting: Rate limiting helps protect an API from overuse or abuse by limiting the number of requests a user can make within a certain timeframe.
  • Caching: Caching helps improve the performance of an API by storing a copy of a response for a certain period and reusing it for future requests.
  • Data Validation: Data validation ensures that the data sent to the API is in the correct format and only contains valid data.
  • Documentation: Documentation helps developers understand how to use the API and what kind of data to send.
  • Error Handling: Error handling helps developers handle errors that may occur when using the API.
  • Security: Security helps protect an API from malicious requests and unauthorized access.

Types of API:

There are four main categories of APIs:

What is an API
  1. Open APIs: Open APIs, usually called external or public APIs, are freely accessible to developers and other users. They are designed to allow access to data or services by other users, such as developers at other businesses. They may be open or need registration and the usage of an API key.
  2. Partner APIs: Partner APIs are conceptually comparable to open APIs but typically have limited access, frequently managed by a third-party API gateway. They are typically created with a specific objective, such as granting access to a service that costs money. This pattern is highly prevalent in the ecosystem of software as a service.
  3. Internal APIs: Internal APIs are intended to be hidden from outside users in contrast to open APIs. They are used to exchange resources within an organization. They enable several teams or divisions of a company to use each other's resources, such as data and software. Compared to traditional integration methods, using internal APIs has several benefits, including security and access control, a record of system access, and a uniform interface for integrating various services.
  4. Composite APIs: Developers can call many endpoints simultaneously using composite APIs. These could be many API endpoints, several services, or distinct data sources. Composite APIs are extremely helpful when a user needs data from multiple services to complete a single operation in a microservice architecture. One call to a composite API can return all the data a user requires, which reduces server load and enhances application performance.

Communication level of APIs

There are two categories of communication level APIS exist:

High-Level APIs:

High-level APIs are application programming interfaces that provide abstractions of a particular application or service. These APIs are designed to make it easier for developers to interact with the application or service and to reduce the amount of code they need to write. Examples of high-level APIs include the Google Maps API, the Facebook Graph API, and the Amazon Web Services API.

Low-Level APIs:

Low-level Application Programming Interfaces (APIs) allow direct access to a computer system's hardware and software components. They are often used to create complex software applications that can access the most basic levels of a system's functions and data. Low-level APIs are typically written in a language that is closer to the language of the system's hardware and software components, such as C and assembly. They can provide an interface to the most basic functions of a computer system, such as memory, storage, networking and input/output. Low-level APIs are often used to create specialized software programs and drivers that require direct access to the system.

What is Web API?

As the name suggests, a web API is an API that can be accessed on the web using the HTTP protocol. This framework aids in the development of HTTP-based RESTFUL services. Web API can be utilized by both web servers and web browsers. A concept for web development is web API. It does not include information about a web server or browser and is just concerned with the client side of Web applications. Web API services are used to deliver services on a variety of devices, including laptops, mobile phones, and other devices, and if an application is to be used on a distributed system. A web API is the enhanced version of an online application.

Two categories of Web APIs are:

  1. Server-side: Server-side web API is a programming interface that enables the communication between a server and a web application. It provides a way for the server to request information from the web application and receive a response from the web application. The API can also be used to send data from the server to the web application. Server-side web APIs are used in web development to allow the web application to interact with external services such as databases, file systems, and external web services.
  2. Client-side: Client-side web APIs are sets of web browser-based application programming interfaces (APIs) that enable web applications to interact with a user's web browser, like controlling the browser's history, managing cookies, and manipulating the user interface itself. Examples of client-side web APIs include the XMLHttpRequest object, the Fetch API, and the Geolocation API.

Some examples of Web API

  1. Google Maps APIs: Using a JavaScript or Flash interface, Google Maps may be integrated into Web pages using Google Maps APIs.
  2. YouTube APIs: Google's API enables developers to incorporate YouTube and its features into websites and software. The YouTube analytics API, YouTube Data API, YouTube live streaming API, YouTube player APIs, and others are examples of YouTube APIs.
  3. The Flickr APIs: Developers can access the Flickr photo-sharing community data by using these APIs.
  4. Twitter APIs: Twitter provides two APIs, the REST API and the search API. The REST API enables developers to access core Twitter data, while the search API gives them ways to engage with the search and trend data on Twitter.

API Architectures and Protocols

An API protocol outlines the guidelines for API requests, including acceptable commands and acceptable data formats. Different API architectures specify various restrictions on communication.


The REST (representational state transfer) architecture is a popular web API architecture. To be categorized as a REST API, an API must adhere to specific architectural restrictions or principles, such as:

Client-server architecture: the backend and data storage are isolated from the interface. This enables flexibility and the independent evolution of many components.

  • Statelessness: The server does not keep track of the client context between requests.
  • Clients can cache responses; therefore, a REST API answer must declare whether it can be cached explicitly.
  • Layered system: The API will function whether speaking to a server directly or via an intermediate, such as a load balancer.
What is an API


RPC stands for a remote procedural call. While JSON-RPC employs JSON for encoding, XML-RPC uses XML to do so. Neither protocol is complicated. One result is anticipated from a call, which may include several parameters. They possess a few critical characteristics that call for an alternative architecture to REST, including:

  • Unlike REST protocols, which require document transfers, they are intended to call methods (resource representations). REST deals with resources, whereas RPC is about actions, to put it another way.
  • The URI identifies the server but doesn't include any information in its parameters, unlike REST, where the URI includes information like query parameters.
What is an API


SOAP (simple object access protocol) is a well-known web API protocol. It is meant to be independent, neutral (able to work with various communication protocols, including HTTP, SMTP, and TCP), and expandable (it allows for any programming style). Included in the SOAP specifications are the following:

  • The processing model: how a SOAP message should be handled.
  • Extensibility model: Modules and characteristics of SOAP.
  • Protocol binding rules: understanding how to utilize SOAP with an underpinning protocol, like HTTP.
  • Message construct: how a SOAP message should be formatted.
What is an API

API Testing tools

API testing involves using software to evaluate how APIs are constructed to ensure the program's functionality, reliability, security, and performance are not compromised. It checks to see if the APIs are working properly and achieving their intended purpose.

Let's see some of the best API Testing tools:

1. Apigee

Apigee is an intriguing cross-cloud API testing platform driven by JavaScript that allows developers and testers to access its capabilities using several editors. This tool is suitable for APIs that include a lot of data, which makes it the ideal option for complex and robust digital organizations. By examining API traffic, response times, and potential error rates, it may also quickly spot problems that are impairing performance.

What is an API

2. SoapUI

SoapUI was developed for advanced users who wanted to create more intricate automated tests and manual calls when necessary. However, thanks to SoapUI's graphical testing interface, novice testers and developers may also catch up. Users can drag and drop pieces to build their tests rather than write the API calls in code. There are two versions of SoapUI: SoapUI Open Source, a cost-free utility, and ReadyAPI, a premium tool.

What is an API

3. Katalon

Katalon is a well-known test automation tool for APIs, online applications, and desktop and mobile apps. It offers numerous parameterization capabilities and commands and supports SOAP and REST calls. One of this software's major benefits is that, despite its many valuable functions, it is not overly complicated to use, making it appropriate even for non-techies.

What is an API

4. Postman

Postman does not necessitate the learning of a new language by developers or testers, and it also supports a variety of forms (such as Swagger and RAML). Additionally, it offers pre-built workspaces, collections, and tools. Developers and testers can skip the text into the command line window since Postman, unlike CURL, is not a command-line-based application.

What is an API

5. Tricentis

Tricentis has developed a comprehensive software testing platform that provides continuous testing capabilities for any application across any technology stack. This platform integrates existing development and DevOps processes to enable comprehensive end-to-end testing. It covers all aspects of testing, including functional, non-functional, performance, security, and exploratory testing. It supports both manual and automated testing and provides tools for team collaboration. Additionally, it provides comprehensive test analytics and reporting capabilities to track and improve quality.

What is an API

6. Assertible

Assertible is a cloud-based platform that enables software teams to monitor, test and deploy applications and services quickly and effectively. It helps teams quickly identify and diagnose problems and rapidly deploy updates. Assertible is designed to be easy to use and to provide real-time feedback on the performance of applications and services. It also gives users insights into their applications and service's behavior, helping them identify and address potential issues.

What is an API

Applications of API

  • Payments: APIs are used to process payments, send invoices, and manage transactions.
  • Social Media: APIs are used to access and display content from social media channels such as Facebook, Twitter, and Instagram.
  • Messaging: APIs are used to send and receive messages, including text messages, chat messages, and emails.
  • Maps: APIs are used to display maps and directions and search for nearby points of interest.
  • Analytics: APIs track user behaviour, analyze data, and generate insights.
  • Security: APIs implement authentication and authorization protocols to secure websites and applications.
  • Mobile Apps: APIs are used to create apps and access device hardware and software features.
  • Cloud Computing: APIs integrate cloud computing services with websites and applications.
  • Banking: Banking APIs allow customers to access their bank account data and make payments directly from third-party applications.
  • Geolocation: Geolocation APIs enable developers to get the user's location to provide relevant content and services. This can be used for anything from local weather information to directions to nearby stores.

Challenges of using APIs

  • Security and Authentication: APIs must be secured and authenticated to protect user data from malicious users. This can be done through tokens, SSL encryption, and other means of authentication.
  • Versioning: As APIs evolve and new features become available, it is important to maintain versioning of the API so that existing applications don't break when new features are added.
  • Documentation and Support: Clear, concise documentation and support are essential for developers using an API. If the documentation needs to be completed or updated, developers may have a difficult time using the API.
  • Scalability: The API provider needs to scale up and down to accommodate the number of users and requests. If the API can handle the load, it can lead to faster performance and even downtime.
  • Performance: Ensuring that the API is performant is key to providing a good user experience. This requires optimization of the code, caching, and other techniques to ensure that the API responds quickly.
  • Error Handling: Error handling is an important but often overlooked component of API design. APIs must handle errors gracefully and present users with helpful information.

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