What Is Web API in .NET? Explained Simply (ASP.NET Core Web API)

Introduction

In modern software development Web API in .NET plays an important role, applications rarely work alone. Websites, mobile apps, and desktop applications often need to communicate with a backend system to send and receive data. This is where Web API in .NET plays an important role.

Web API in .NET is a framework that allows developers to build HTTP-based services that can be accessed by different types of clients such as web browsers, mobile applications, desktop apps, and third-party systems. It enables smooth communication between the frontend and backend by exchanging data, usually in JSON format.

One of the biggest advantages of Web API is that it is platform independent. This means a .NET Web API can serve data to applications built using Angular, React, Vue, Android, iOS, or any other technology. The client does not need to know how the backend is built; it only needs to send HTTP requests and receive responses.

In the .NET ecosystem, Web API is commonly built using ASP.NET Core Web API, which is lightweight, fast, and designed for modern, scalable applications. It follows REST principles and supports standard HTTP methods such as GET, POST, PUT, and DELETE, making it easy to perform CRUD (Create, Read, Update, Delete) operations.

A Web API (Application Programming Interface) A Web API in .NET is a way for different applications to talk to each other over the internet using HTTP.

In simple terms, a Web API allows one application to request data and another application to send data back. This communication happens using standard web requests, just like when you open a website in a browser.

Using .NET Web API, developers can create services that can be used by:

• Websites
• Mobile applications
• Desktop applications
• Other servers

Web API is fast, lightweight, and can be used on different platforms, which makes it very popular in modern application development.

Client–Server Concept in Web API

Web API follows the client–server architecture, where responsibilities are clearly separated.

1. Client:

The client is the application that sends a request.
Examples of clients:

2. Server:

The server hosts the Web API and processes incoming requests.
It handles business logic, database operations, and returns the response to the client.

How it works:

1.The client sends an HTTP request (GET, POST, PUT, DELETE).
2.The Web API processes the request.
3.The server sends back a response with data or status information.

This separation improves scalability, security, and maintainability of applications.

Data Formats Used in Web API (JSON)

Web APIs exchange data using standard data formats, and the most commonly used format is JSON (JavaScript Object Notation).

Why JSON is preferred:

• Lightweight and fast
• Easy to read and understand
• Language independent
• Supported by almost all platforms and programming languages

Example of JSON response:

{
  "id": 1,
  "name": "TestName",
  "email": "test@example.com"
}

.NET Web API uses JSON by default to send and receive data, making it ideal for modern web and mobile applications.

Why Use Web API?

Using Web API in .NET helps developers build modern, fast, and flexible applications. It is widely used in real-world projects because it makes communication between systems easy and efficient.

Allows Communication Between Different Applications

A .NET Web API allows different applications to communicate with each other, even if they are built using different technologies.

Example:

• A mobile app requests user data
• A website displays product information
• A desktop application connects to the same database

All these applications can use the same Web API to get or send data.

HTTP Methods In Web API (GET, POST, PUT, DELETE)

Web API uses standard HTTP methods, which makes it easy to understand and work with.

Works with Modern Frontend Frameworks

.NET Web API works very well with modern frontend technologies such as:

• Angular
• React
• Vue
• Mobile apps (Android & iOS)

Frontend applications use Web API to get data from the server and show it to users.
We can perform insert, update ,delete operations using web API.

Easy to Maintain and Scale

Web API separates the frontend and backend, which makes applications:

• Easy to maintain
• Easy to update
• Easy to scale for more users

Developers can change the backend without affecting the frontend, and vice versa.

How Web API in .NET Works

let’s see how web API works in a simple way.

Web API acts as a middle layer between the client (frontend) and the database.

Simple flow

1. The client (Angular, React, mobile app, etc.) sends an HTTP request.
2. The Web API receives and processes the request.
3. The Web API interacts with the database if needed.
4. The Web API sends a response back in JSON format.

Example flow

Angular App → .NET Web API → Database → JSON Response

This flow makes applications faster, secure, and easier to manage.

Difference Between Web API and MVC

Many beginners get confused between ASP.NET MVC and WEB API
Here is a simple comparison:

MVC	WEB API
MVC returns view and data	WEB API returns JSON data
Focused on user interface	Focused on data
Used for web pages	Used for API’s and services
Frontend and backend combine	Frontend and backend separated
Building full web application	Building HTTP services
IIS environment required for hosting	Self hosting support

In short :

• MVC is used to build websites
• Web API is used to build services for app

ASP.NET Core Web API Example

Now we will create simple controller and see the response on the localhost URL

EmployeeController.cs

using Microsoft.AspNetCore.Mvc;

namespace DemoWebAPI.Controllers
{
    [ApiController]
    [Route("api/[controller]")]
    public class EmployeeController : ControllerBase
    {
        // GET: api/employee
        [HttpGet]
        public IActionResult GetEmployee()
        {
            var employee = new
            {
                Id = 101,
                Name = "Amit Sharma",
                Department = "IT",
                Designation = "Software Engineer"
            };

            return Ok(employee);
        }
    }
}

API URL

https://localhost:5001/api/employee

Sample JSON Response

{
  "id": 101,
  "name": "Amit Sharma",
  "department": "IT",
  "designation": "Software Engineer"
}

Explanation

In the above example, we have created a simple EmployeeController in ASP.NET Core Web API.

The [ApiController] attribute used to automatic model validation.
The [Route(“api/[controller]”)] attribute defines the route for this controller. it is the attribute base routing.
In this case, the route becomes api/employee.

The GetEmployee() method is decorated with the [HttpGet] method, which means it will handle HTTP GET requests.

Inside the method, we return a sample employee object using the Ok() method, which sends a 200 OK response along with JSON data.

How to Test the Web API

Now we see how to test web API

Test using browser

1.Run the application.

Open a web browser.

1.Run the application.
2.Open a web browser.
3.Enter the API URL: https://localhost:5001/api/employee
4.Press Enter.

Now you will see the JSON response displayed in the browser.

Advantages of ASP.NET Core Web API

ASP.NET Core Web API provides many benefits for modern application development

This are the all advantages of ASP.NET Core Web API.

Real-World Use Cases of Web API

Web API is used in many real-world applications

• Mobile and web application fetching data from a server
• E-commerce websites managing all products and orders
• Banking and financial applications
• Microservices Architecture
• Call third party API using httpclient

Frequently Asked Questions (FAQ)

Q1. What is a Web API in .NET?

A Web API in .NET is a bridge between application and database. it is a framework to build HTTP based services
that can be access by mobile application, web application.

Q2. How is ASP.NET MVC different from Web API?

ASP.NET MVC is used to create web pages and User Interface. Web API, on the other hand,
is used to send and receive data (JSON data) without any UI.

Q3. Is ASP.NET Core Web API RESTful?

Yes, it follows REST principles. We can use HTTP methods – GET, POST, PUT, DELETE, and PATCH to perform CRUD operations on data.

Q4. Why do Web APIs use JSON?

JSON is lightweight and easy to read. It works well with JavaScript and is supported by almost every programming language,
making it the most common format for APIs.

Q5. Can I use ASP.NET Core Web API with Angular or React?

Sure you can use with Angular, React, and Vue can call the API to fetch data, insert data and update the data With frontend.

Q6. Is ASP.NET Core Web API cross-platform?

Yes. It runs on multiple operating systems like Windows, Linux, and macOS without any changes.

Q7. What tools can I use to test Web API?

You can test Web API using a web browser, Postman, or Swagger.

Conclusion

Web API in .NET is a powerful and flexible way to build backend services that can be used by multiple types of applications. It allows smooth communication between the client and server using standard HTTP methods and JSON data.

In this article we learned:

• What Web API is in .NET
• How client–server architecture works
• Why JSON is used
• Difference between MVC and Web API
• A basic example of ASP.NET Core Web API

Related Blogs You Might Like

• Difference between .NET framework, .NET Core & .NET 8– Learn different .NET versions.
• What is .NET Full Stack Development? Beginner Guide – Understand the full .NET full stack development.