A Web API (Application Programming Interface) is a system of tools and protocols that allows different software applications to communicate with each other over the web. It acts as a bridge between the client (frontend) and the server (backend), enabling the transfer of data or functionality without requiring the client to know how the server works internally.

Key Concepts:

1. Client-Server Model:

   • The client (usually a browser or mobile app) sends a request to the server using an API, and the server responds with the required data or actions.
   • Common protocols used include HTTP/HTTPS.

2. Endpoints:

   • Endpoints are specific URLs where the API receives requests.
   • Example: https://api.example.com/users might be an endpoint for retrieving a list of users.

3. HTTP Methods: Web APIs use standard HTTP methods to define the type of action to be performed:

   • GET: Retrieve data from the server.
   • POST: Send data to the server (often for creating a resource).
   • PUT: Update an existing resource on the server.
   • DELETE: Remove a resource from the server.

4. Request and Response:

   • Request: Contains the method (GET, POST, etc.), endpoint, headers (e.g., authentication tokens), and possibly a body (in POST/PUT requests) with data.
   • Response: The server sends back a response, typically in JSON or XML format, which includes status codes (e.g., 200 for success, 404 for not found).

5. REST (Representational State Transfer):

   • One of the most common architectural styles for Web APIs.
   • REST APIs are stateless and use simple URL endpoints combined with HTTP methods to perform CRUD (Create, Read, Update, Delete) operations.

6. Authentication:

   • APIs often require authentication to control access.
   • Common methods include API keys, OAuth, and JWT (JSON Web Tokens).

7. JSON (JavaScript Object Notation):

   • A lightweight format used for data interchange in APIs. It's easy to read and write, making it the most commonly used format in web APIs.

Example of a Simple Web API Request:

To get a list of users from an API, you might send a GET request to an endpoint like:

The response would look something like: