What is API? The Complete Guide For API

What is API? The Complete Guide For API

API stands for Application Programming Interface. The concept of API was developed to establish Secure, Scalable, and Easy Data Transfer.


10 min read

Today's world is relay on the Internet. And the Internet is all about sharing data and information. But as the internet grows sharing information is getting hard and vulnerable. To establish a secure and easy communication way, developers create API. API stands for Application Programming Interface. The concept of API was developed to establish Secure, Scalable, and Easy Data Transfer between two systems.

Types of API Architecture

We can distribute APIs based on their architecture. API architecture defines rules and guidelines for data sharing. There are mostly three API architectures are there:

  1. REST APIs

  2. SOAP APIs

  3. RPC APIs


REST means Representational State Transfer. Today the majority of APIs are built upon REST Architecture. REST APIs define guidelines for easy, scalable, and lightweight data transfer. APIs using these guidelines are called REST APIs. There are main five guidelines in REST Architecture.

How REST APIs Work

  1. Client-Server Separation - REST follows strict Client-Server separation. Request must come from Client and Response must sent from Server. This Response and Request condition should be strictly followed by REST APIs. The client cannot respond and the same Server cannot send the request.

  2. Uniform Interface - All REST APIs must only use HTTP Protocol for communication. All Requests and Responses should be formatted in a specific way to ensure compatibility between the Client and Server. All Server responses must be formatted using JSON (Javascript Object Notation).

  3. Stateless - Each Client-Server interaction should be independent of current simultaneous interactions as well as past interactions. The server should not store any current or previous data from client requests.

  4. Layered System - All the Requests and Responses must always be formatted the same way, even when passed through intermediate servers between the client and the API.

  5. Cacheable - All server responses should indicate whether a provided resource can be cached by the client and for how long. Servers store frequently used data in cache to load them faster. Which greatly improves the performance of REST APIs.


SOAP means Simple Object Access Protocol. SOAP is Protocol as well as Architecture which is used for transmitting data across networks. SOAP protocol is standardized by the World Wide Web Consortium (W3C). It utilizes XML (Extensible Markup Language) to encode information. SOAP Protocol is much stricter in nature compared to REST. This strict behaviour makes SOAP APIs more secure than REST. But this strict nature is code-heavy and harder to implement. SOAP messages are larger and more complex in nature which makes them slower in performance. SOAP APIs are mostly used for internal data transfer and security-intensive transfer. One of the biggest advantages of SOAP APIs is they work on almost every communication protocol. (REST APIs only work with HTTP Protocol).

How SOAP APIs Works

SOAP Protocols define strict communication rules. W3C defines several standards to control every aspect of the data exchange. Below are some standards that SOAP uses:

  1. WS-Security specifies security measures like using unique identifiers called tokens

  2. WS-Addressing requires including routing information as metadata

  3. WS-Reliable Messaging standardizes error handling in SOAP messaging

  4. WSDL describes the scope and function of SOAP web services

While sending an HTTP request, we just need to wrap our request to SOAP Envelope. SOAP Envelope modifies the HTTP content as per SOAP requirements. This capability of SOAP Envelope enables SOAP to use a wide range of protocols like HTTP, TCP, SMTP and ICMP. However, SOAP web services always return responses in XML Format only.


RPC means Remort Procedural Call. RPC protocols are used to invoke scripts on the server. It is like executing a block of code on another server. RPC is very rarely used. Hence you will not see it on a day-to-day basis.

Difference Between REST API and SOAP API

Representational State TransferSimple Object Access Protocol
REST is an architectureSOAP is a protocol
REST only works with HTTP ProtocolSOAP works on any transfer protocol
REST widely used JSON. But supports XML, Plain
Text and HTML as wellSOAP only supports XML
REST has a faster performanceSOAP is slower in performance
REST is easy to scaleSOAP is harder to scale
REST Supports encryption without affecting performanceSOAP Supports encryption but affairs on performance
REST is mostly used in Public APIsSOAP is used for Internal APIs. Where Security is the top-most priority

Similarities Between REST API and SOAP API

  • REST and SOAP both APIs describe rules and standards for data transfer.

  • REST and SOAP both use HTTP Protocol. (XML Supports other protocols as well)

  • REST and SOAP both use SSL/TLS for secure communication.

When to use SOAP API

Both REST and SOAP are powerful APIs. Always choose your requirements to finalize which one to choose. But You can consider the below points to finalize:

  • High-Security Requirements - If you are developing private APIs where security is your priority. If you are okay with losing some performance then SOAP might be a good option. Because SOAP APIs have Built-in compliance for ACID (Atomicity, Consistency, Isolation and Durability). Which makes SOAP APIs suitable for High-Security and High-Integrity requirements.

  • To Support a Wide Range of Transfer Protocols - If your API needs to support a wide range of transfer protocols then SOAP is the best option. SOAP APIs are independent of Transfer Protocols. Apart from famous Protocols like HTTP, SOAP APIs support SMTP (Simple Mail Transfer Protocol), JMS (Java Messaging Services) and other transfer protocols as well.

  • Need Chained Operations - If your API is dependent on Chained Operation then SOAP is the only way to go. As SOAP APIs are statuful. This means the server stores information about Requests and Responses. This helps SOAP APIs to perform chained operations. Chained Operations require previous data to perform the next request. This thing makes SOAP APIs resource and bandwidth-heavy. But some tasks require Chain Operations like Bank Transfers.

TLDR - If you want to support a wide range of protocols and High-Security go with SOAP API. And if you want Flexibility and Performance then go with the REST API.

When to use REST APIs

REST APIs are usually used when you need flexibility and performance. Below are some use cases in which REST is the best fit:

  • For Public APIs - REST APIs provide us Scalability, Performance and Flexibility which makes it the best fit for Public APIs. Also, REST Supports JSON format which is easy to understand and use. REST lacks some built-in security features but you can use third-party ways to overcome this flow.

  • When you need Lightweight and Performant APIs - REST APIs are best when you want APIs to be lightweight. REST APIs are stateless. This means they don't store any past request-response data. The server treats every request as a brand-new request. Which makes REST APIs Efficient and Performant. Data can be cached in REST APIs. Server stores frequently used data in cache which also helps in Performance. REST APIs also support the large number of Data Formats like JSON, XML, HTML and Plain Text.

Types of APIs

Till now we understand the importance and usage of APIs in our world. They are one of the important driving forces of today's internet. Now let's talk about types of APIs. We can differentiate APIs into three major categories:

  • Public APIs - Public APIs also known as Open APIs are available for public use. Any developer can access it, use it and read its documentation. Generally, Public APIs are uses less authentication and less authorization to access their data. But some Public APIs offer a limited free tier and then based on the volume of calls they charge to developers as well. It is not like that all Public APIs are completely free. As a developer, we use many Public APIs in our day-to-day life to make our apps feature-rich. Some famous Public APIs are Random User Generator, Open Weather, and JSON Placeholder.

  • Private APIs - Private APIs are also known as Internal APIs. These APIs are usually used inside an organization for internal purposes. Private APIs never expose any kind of information to the public. Also, they are highly secured as well. Almost every major company has Multiple Private APIs.

  • Partner APIs - Partner APIs are APIs which are paid APIs. These APIs are highly secured. Companies share these APIs with customers who purchase their services. Only authorized customers get the details of these APIs.


In conclusion, APIs (Application Programming Interfaces) play a crucial role in today's world, enabling secure and efficient data transfer between systems. They provide a standardized framework for communication, allowing developers to create applications that can interact with each other seamlessly. In this blog, we explored three major types of API architectures: REST APIs, SOAP APIs, and RPC APIs.

REST APIs, based on the Representational State Transfer architecture, are the most widely used APIs today. They offer a lightweight and scalable approach to data transfer, utilizing the HTTP protocol and JSON formatting. REST APIs follow the principles of client-server separation, uniform interface, statelessness, layered system, and cacheability. These guidelines contribute to their performance, ease of use, and compatibility.

SOAP APIs, on the other hand, are based on the Simple Object Access Protocol. SOAP is a more strict and heavyweight protocol, that uses XML for data encoding. SOAP APIs are known for their high-security features and support for various communication protocols beyond HTTP. They adhere to standards such as WS-Security, WS-Addressing, WS-Reliable Messaging, and WSDL. SOAP APIs are commonly used for internal data transfer within organizations, where security is a top priority.

RPC APIs, which stand for Remote Procedure Calls, are less commonly used in comparison to REST and SOAP APIs. RPC protocols enable the execution of scripts on remote servers, allowing for the invocation of code blocks on another system. While RPC APIs offer certain capabilities, they are not as prevalent in day-to-day use.

When comparing REST and SOAP APIs, REST APIs are favoured for their performance, scalability, and flexibility. They are suitable for public APIs, as they support various data formats and provide lightweight communication. SOAP APIs, on the other hand, are recommended for scenarios with high-security requirements and the need to support a wide range of transfer protocols. SOAP APIs excel in scenarios where chained operations and compliance with ACID principles are necessary.

Ultimately, the choice between REST and SOAP APIs depends on the specific requirements of the project at hand. REST APIs are well-suited for public APIs and scenarios that prioritize performance and flexibility. SOAP APIs are ideal for internal APIs within organizations, where security is paramount, and when a wider range of transfer protocols is needed.

Lastly, we discussed the three major types of APIs: public APIs, private APIs, and partner APIs. Public APIs are openly available for use by developers and often provide limited free access, while private APIs are used internally within organizations and offer higher levels of security. Partner APIs are paid APIs that are shared with authorized customers and offer enhanced security measures.

In conclusion, APIs have revolutionized the way data is shared and have become an integral part of modern-day Internet infrastructure. Understanding the different types of API architectures and their respective use cases allows developers to make informed decisions when designing and implementing their applications. The continuous advancement and adoption of APIs contribute to the growth and innovation of the digital landscape, enabling seamless integration and collaboration between diverse systems and services.

So, guys, That’s all you need to know about APIs. Please let me know if I miss something. I’ll be happy to learn from you. Till Then Keep Loving, Keep Coding. I’ll surely catch you up in the next article. Jai Hind, Vande Mataram 🇮🇳

Remember no teacher, no book, no video tutorial, or no blog can teach you everything. As one said Learning is Journey and Journey never ends. Just collect some data from here and there, read it, learn it, practice it, and try to apply it. Don’t feel hesitant that you can’t do that or you don’t know this concept or that concept. Remember every programmer was passed from the path on which you are walking right now. Remember Every Master was Once a Beginner. Work hard and Give your best.

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