What is an API?

An API (Application Programming Interface) is a set of rules and protocols that allows different software components to communicate with each other. In simple terms, APIs allow applications to interact, share data, and perform tasks without needing direct user interaction.

Why Are APIs Important in Backend Development?

APIs are critical in backend development because:

• They facilitate communication between the client-side (frontend) and server-side (backend).
• They enable modular development, allowing different services to work independently.
• APIs can be exposed for third-party integration and allow external systems to interact with your app.

What is HTTP?

HTTP (Hypertext Transfer Protocol) is the foundation of any data exchange on the web, and it's a protocol used by APIs to send and receive data. It operates over a client-server model where a client sends a request, and the server sends back a response.

Key HTTP Methods

Method	Description	Example
GET	Retrieves data from a server	Fetch user information
POST	Sends new data to a server	Submit a registration form
PUT	Updates existing data on a server	Update user profile
DELETE	Deletes existing data on a server	Remove a user account

HTTP Status Codes

Code	Description	Example
200	OK - The request was successful	Data retrieved successfully
201	Created - A new resource has been created	User created after a POST request
400	Bad Request - Invalid input	Missing required fields in the request body
404	Not Found - Resource not found	User not found with the given ID
500	Internal Server Error - Server crashed	Unexpected error occurred on the server

Basic Concepts: RESTful APIs

What is a RESTful API?

A RESTful API is an API that follows the principles of REST (Representational State Transfer), which is a lightweight, scalable, and flexible architecture commonly used for building web services. REST APIs primarily use HTTP requests to perform CRUD operations (Create, Read, Update, Delete) on resources.

Principles of REST

1. Stateless: Each request from the client to the server must contain all the necessary information to understand and process it.
2. Client-Server Architecture: The client and server are separate entities that communicate over HTTP.
3. Uniform Interface: The same method should be used to interact with resources.
4. Resource Representation: Resources are represented via URIs (Uniform Resource Identifiers).
5. Cacheable: Responses can be cached to improve performance.

Example: REST API for User Management

Method	Endpoint	Description
GET	/api/users	Retrieve all users
GET	/api/users/{id}	Retrieve a single user by ID
POST	/api/users	Create a new user
PUT	/api/users/{id}	Update user by ID
DELETE	/api/users/{id}	Delete user by ID