## What are RESTful APIs?
REST (Representational State Transfer) is an architectural style for designing networked applications. RESTful APIs follow a set of principles that make them scalable, maintainable, and easy to understand.
## Core Principles of REST
**Resource-Based**: Everything is a resource (users, products, orders) identified by URLs. For example, `/users/123` represents user with ID 123.
**Standard HTTP Methods**: Use GET to read, POST to create, PUT/PATCH to update, DELETE to remove resources.
**Stateless**: Each request contains all information needed to process it. The server doesn't store client state between requests.
**Client-Server Separation**: Frontend and backend evolve independently as long as they agree on the API contract.
## How REST Works in Practice
When building an e-commerce application:
- `GET /products` retrieves all products
- `GET /products/42` retrieves a specific product
- `POST /products` creates a new product
- `PUT /products/42` updates product 42
- `DELETE /products/42` removes product 42
The HTTP method tells the server what operation to perform, and the URL identifies which resource to act on.
## Why REST Became the Standard
**Simplicity**: Uses familiar HTTP protocols that every web developer understands.
**Cacheability**: GET requests can be cached by browsers and CDNs, improving performance.
**Scalability**: Stateless nature makes it easy to distribute load across multiple servers.
**Flexibility**: Works with any data format (JSON, XML, HTML), though JSON is most common today.
## HTTP Status Codes
REST APIs communicate results through standard HTTP status codes:
- **200 OK**: Request succeeded
- **201 Created**: New resource created
- **400 Bad Request**: Client sent invalid data
- **401 Unauthorized**: Authentication required
- **404 Not Found**: Resource doesn't exist
- **500 Internal Server Error**: Server encountered an error
## Best Practices
**Use Nouns, Not Verbs**: URLs should represent resources (`/users`) not actions (`/getUsers`).
**Versioning**: Include API version in URLs (`/api/v1/users`) to maintain backward compatibility.
**Filtering and Pagination**: For large datasets, support query parameters like `/products?category=electronics&page=2`.
**Consistent Naming**: Use plural nouns (`/products`, not `/product`) and maintain consistent conventions.
## Real-World Example
Stripe's payment API is a excellent example of RESTful design. Creating a payment involves `POST /v1/charges` with payment details, while retrieving payment history uses `GET /v1/charges?customer=cust_123`. Each endpoint is intuitive, and the HTTP methods clearly indicate the operation.
## REST vs Alternatives
While REST dominates, alternatives exist:
- **GraphQL** offers more flexible queries but adds complexity
- **gRPC** provides better performance for internal services
- **WebSockets** enable real-time bidirectional communication
REST remains the go-to choice for most public APIs due to its simplicity and universal understanding.
