# REST APIs

**REST** (Representational State Transfer) is an architectural style for building web services. A **REST API** (Application Programming Interface) allows different software applications to communicate with each other over the internet using standard HTTP methods.

## 1. How it Works

REST APIs function on a **Client-Server** model:
*   **Client:** The application (web browser, mobile app) making the request.
*   **Server:** The computer storing the data and logic that processes the request.

The client sends a **Request** to a specific URL (Endpoint), and the server sends back a **Response** (usually data in JSON format).

## 2. HTTP Methods (Verbs)

REST APIs use standard HTTP verbs to perform actions on resources.

*   **GET:** Retrieve data from the server. (e.g., Get a list of users)
*   **POST:** Send data to the server to create a new resource. (e.g., Create a new user)
*   **PUT:** Update an entire existing resource. (e.g., Update a user's full profile)
*   **PATCH:** Update part of an existing resource. (e.g., Update just a user's email)
*   **DELETE:** Remove a resource from the server. (e.g., Delete a user)

## 3. HTTP Status Codes

The server responds with a numeric code indicating the result.

*   **2xx Success:**
    *   `200 OK`: Request succeeded.
    *   `201 Created`: Resource successfully created.
*   **4xx Client Error:**
    *   `400 Bad Request`: The server couldn't understand the request.
    *   `401 Unauthorized`: Authentication failed or missing.
    *   `404 Not Found`: The requested resource doesn't exist.
*   **5xx Server Error:**
    *   `500 Internal Server Error`: Something went wrong on the server side.

## 4. Data Format (JSON)

While REST can use XML, **JSON** (JavaScript Object Notation) is the standard format for modern APIs because it is lightweight and easy to parse.

### Request Example
```http
POST /api/users HTTP/1.1
Host: api.example.com
Content-Type: application/json

{
  "name": "Alice",
  "email": "alice@example.com"
}
```

### Response Example
```json
{
  "id": 101,
  "name": "Alice",
  "email": "alice@example.com",
  "createdAt": "2023-10-27T10:00:00Z"
}
```

[[programming/asynchronous-programming]]
[[programming/database-basics]]