Almost every modern application depends on APIs.
Your mobile app talks to a backend through an API.
A React frontend communicates with a Spring Boot server through an API.
Third-party applications integrate with services through APIs.
Among the different approaches to building APIs, REST became one of the most widely adopted.
But why?
What made REST so popular?
The answer isn't simply that REST is easy to use. Its popularity comes from a combination of simplicity, scalability, flexibility, and compatibility with the web itself.
First, What Is a REST API?
REST stands for Representational State Transfer.
It isn't a programming language, framework, or protocol.
It's an architectural style for designing networked applications.
A REST API typically exposes resources through URLs and uses standard HTTP methods to interact with those resources.
For example:
GET /api/users
GET /api/users/101
POST /api/users
PUT /api/users/101
DELETE /api/users/101
The API represents things as resources:
/users
/products
/orders
/payments
And HTTP methods describe what we want to do with those resources.
REST Uses Something the Web Already Understands
One of REST's biggest advantages is that it builds on HTTP.
Developers don't need to learn an entirely new communication protocol.
They already understand concepts such as:
- GET
- POST
- PUT
DELETE
200 OK
201 Created
400 Bad Request
401 Unauthorized
404 Not Found
500 Internal Server Error
REST uses these existing web standards rather than reinventing them.
That's a major reason it became so accessible.
Simple Client-Server Communication
Consider a React application requesting a user's profile.
The frontend might send:
GET /api/users/101
The backend processes the request and returns something like:
{
"id": 101,
"name": "Ajeet",
"role": "Developer"
}
The frontend doesn't need to know how the backend retrieves the data.
The backend doesn't need to know how the frontend displays it.
They communicate through a well-defined interface.
This separation is one of the fundamental ideas behind REST.
JSON Made REST Even More Popular
REST APIs can return different representations, but JSON became the dominant format for modern web APIs.
Because JSON is:
- Lightweight
- Human-readable
- Easy to generate
- Easy to parse
- Supported by virtually every programming language
A Java backend can communicate with a JavaScript frontend.
A Python application can communicate with a Java service.
A mobile application can communicate with a Node.js backend.
The technologies don't have to be the same.
As long as they understand HTTP and the data format, they can communicate.
REST Is Language Independent
This is another major reason for its adoption.
Imagine your backend is built with:
- Java + Spring Boot
- Your frontend is:
- React + JavaScript
And your mobile application is:
Android
All three can communicate with the same REST API.
┌── React
│
Client ──────────┼── Android
│
└── Another
Service
↓
REST API
↓
Backend
The API becomes a common communication layer between different technologies.
Statelessness: One of REST's Most Important Ideas
A REST architecture encourages stateless communication.
This means the server doesn't need to remember the client's previous request in order to understand the next one.
Each request contains the information required to process it.
For example:
GET /api/orders
Authorization: Bearer <token>
The server can validate the token and process the request without depending on a specific previous request.
This makes horizontal scaling easier.
You can have:
┌── Server 1
Client → LB ─┼── Server 2
└── Server 3
A request doesn't necessarily need to return to the same server that handled the previous request.
This is particularly useful in distributed and cloud-based systems.
REST and HTTP Status Codes
REST APIs also make good use of HTTP status codes.
For example:
200 OK
The request succeeded.
201 Created
A new resource was created.
400 Bad Request
The client sent an invalid request.
401 Unauthorized
Authentication is required or invalid.
404 Not Found
The requested resource doesn't exist.
500 Internal Server Error
Something went wrong on the server.
These standard status codes provide a common language between clients and servers.
REST Is Easy to Test
Because REST commonly uses HTTP, testing an API is straightforward.
You can use tools such as:
- Postman
- cURL
- Browser developer tools
- Automated API testing frameworks
For example:
https://api.example.com/users/101
You don't need a specialized client just to make a basic request.
This simplicity significantly reduces the barrier to development and debugging.
REST Fits Naturally Into Modern Architectures
REST APIs became especially important as applications moved toward:
- Single Page Applications
- Mobile applications
- Microservices
- Cloud computing
- Distributed systems
A frontend and backend can evolve independently.
For example:
React
↓
REST API
↓
Spring Boot
↓
Database
Later, the same backend API could also serve:
- React
- Android
- iOS
- Another Backend Service
- Third-Party Client
The API becomes a stable boundary between systems.
REST and Microservices
REST also played an important role in the growth of microservices.
Instead of building one massive application, functionality can be separated into different services.
For example:
Order Service
↓
REST API
Payment Service
↓
REST API
User Service
↓
REST API
These services can communicate over HTTP without needing to be written in the same programming language.
This flexibility helped REST become a common choice for service-to-service communication.
But REST Isn't Perfect
REST became popular, but it isn't the solution to every API problem.
Depending on the use case, other technologies may be more appropriate.
For example:
GraphQL can be useful when clients need flexible data queries.
gRPC can be useful for high-performance service-to-service communication.
WebSockets are better suited for persistent real-time communication.
Message queues are useful for asynchronous, event-driven systems.
So the question isn't:
«"Is REST better than everything else?"»
The better question is:
«"Is REST the right tool for this particular problem?"»
Why REST Ultimately Won
REST didn't become popular because it was the newest technology.
It became popular because it worked extremely well with the technologies developers were already using.
It provided:
- Familiar HTTP semantics
- Simple resource-based design
- Language independence
- Easy integration
- Stateless communication
- Standard status codes
- Excellent tooling
- Broad ecosystem support
- Easy frontend and backend integration
Most importantly, REST made it relatively simple for completely different systems to communicate with each other.
The Bigger Picture
Modern software is rarely one application running on one machine.
It's usually a collection of different components:
Frontend
↓
API
↓
Backend Services
↓
Database
↓
External Services
REST provides a simple and standardized way for many of these components to communicate.
That's why, even after decades of new technologies and architectural patterns, REST APIs remain a fundamental part of modern software development.
REST didn't win because it was the most sophisticated approach.
It became popular because it made communication between systems simple, understandable, and practical.
And sometimes, simplicity is exactly what makes a technology scale.
What do you think will become the dominant API style in the next decade: REST, GraphQL, gRPC, or something else?
