API Tutorial: Learn APIs from Basics to Advanced

Introduction to APIs

API stands for Application Programming Interface. It allows different software applications to communicate with each other and exchange data or services through defined rules and endpoints.

What is an API?

An API is a set of rules and interfaces that allows one application to interact with another application or service. In web development, APIs commonly use HTTP to receive requests and return responses. REST APIs are a widely used approach for building web APIs.

Why Learn APIs?

Features of APIs

• Allow different applications and services to communicate.
• Use defined endpoints and request methods to access resources.
• Support request and response-based communication.
• Can use authentication to control access to protected resources.

Advantages of APIs

APIs make it possible to connect different applications without requiring one application to know the internal implementation of another. They support reusable services, data exchange, application integration and communication between frontend and backend systems.

API Use Cases

API vs Website

A website is primarily designed to present content and interfaces for users through a web browser, while an API is designed to allow applications or services to communicate programmatically. An API typically returns structured data such as JSON rather than a complete webpage.

APIs are especially important in full stack development because frontend applications often communicate with backend services through APIs to retrieve, create, update and delete application data. If you want to learn frontend, backend, database and API technologies together, explore our Full Stack Developer Course.

API Request and Response

An API request is a message sent by a client to an API to ask for data or perform an operation. The API processes the request and sends an API response back to the client. This request-response process is the basic communication pattern used by web APIs.

What is an API Request?

An API request contains the information required by the server to process a client operation. A typical HTTP request can include the API endpoint, HTTP method, headers, query parameters and request body.

GET https://api.example.com/users

In this example, the client sends a GET request to the /users endpoint to retrieve user data.

Parts of an API Request

What is an API Response?

An API response is the message returned by the server after processing an API request. A response commonly contains an HTTP status code, headers and data. APIs frequently use JSON to return structured data to the client.

{
  "id": 101,
  "name": "Dhanush",
  "city": "Chennai"
}

Parts of an API Response

API Request and Response Flow

1. The client sends a request to an API endpoint.
2. The API receives and processes the request.
3. The server performs the required operation.
4. The API creates a response containing a status code and data.
5. The client receives and uses the response.

Understanding API requests and responses is essential before learning HTTP methods, status codes, REST APIs and API integration.

HTTP Methods

HTTP methods define the type of operation a client wants to perform through an API. The most commonly used methods are GET, POST, PUT and DELETE.

GET

GET is used to retrieve data from an API.

GET /users

POST

POST is used to send data to an API and create a new resource.

POST /users

PUT

PUT is used to update an existing resource.

PUT /users/101

DELETE

DELETE is used to remove an existing resource.

DELETE /users/101

HTTP Status Codes

HTTP status codes are returned by a server to indicate the result of an API request. They help the client understand whether the request was successful, redirected or resulted in an error.

Status Code Categories

• 2xx: Successful requests.
• 3xx: Redirection responses.
• 4xx: Client-side errors.
• 5xx: Server-side errors.

What is REST API?

REST API stands for Representational State Transfer Application Programming Interface. It is a common approach for building web APIs that allow applications to communicate with each other using HTTP.

REST API Example

GET    /users
GET    /users/101
POST   /users
PUT    /users/101
DELETE /users/101

Here, /users represents a user resource. Different HTTP methods can be used to retrieve, create, update or delete that resource.

Key Features of REST API

• Uses HTTP methods to perform operations.
• Uses URLs or endpoints to identify resources.
• Commonly exchanges data using JSON.
• Allows frontend applications, backend services and other clients to communicate.

REST API Example Response

{
  "id": 101,
  "name": "Dhanush",
  "city": "Chennai"
}

REST APIs are widely used in web applications to connect frontend applications with backend services and exchange application data.

REST API CRUD Operations

CRUD stands for Create, Read, Update and Delete. REST APIs commonly use HTTP methods to perform these operations on resources such as users, products or orders.

CRUD Operations in REST API

CRUD Example

POST   /users       → Create a user
GET    /users       → Get users
PUT    /users/101   → Update user 101
DELETE /users/101   → Delete user 101

CRUD operations are commonly used when building REST APIs for database-driven applications. A backend API can use these operations to manage resources and communicate with frontend applications.

API Testing with Postman

Postman is a tool used to send API requests and check API responses without building a frontend application. It is commonly used to test REST APIs during development.

How to Test an API with Postman

1. Open Postman and create a new HTTP request.
2. Select a method such as GET, POST, PUT or DELETE.
3. Enter the API endpoint URL.
4. Add request data or headers when required.
5. Click Send to make the API request.
6. Check the response, status code and returned data.

Example API Request

GET https://api.example.com/users

After sending the request, Postman displays the API response along with the HTTP status code and response data.

What Can You Test?

• API endpoints and HTTP methods.
• Request and response data.
• HTTP status codes and error responses.
• API authentication and request headers.

API Integration

API integration means connecting one application or service with another through an API. It allows applications to request, send and exchange data between systems.

How API Integration Works

1. The application identifies the required API endpoint.
2. The client sends a request using an HTTP method.
3. The API processes the request and performs the required operation.
4. The API returns a response, commonly in JSON format.
5. The application processes the response and displays or uses the data.

Simple API Integration Example

Frontend Application
        ↓
    API Request
        ↓
    REST API
        ↓
   API Response
        ↓
Frontend displays the data

For example, a frontend application can request product information from a REST API. The API retrieves the required data and returns it as JSON, which the frontend can then display to the user.

Common API Integration Uses