Build Your First ASP.NET Core Web API

Step 1: Create a new Web API project

Open Visual Studio and create a new ASP.NET Core Web API project. Name it FirstWebApi. Choose the current .NET version and keep the default API template enabled so you can start quickly.

Step 2: Understand the goal

Instead of rendering a desktop form, a Web API exposes endpoints that other applications can call. A browser, mobile app, JavaScript frontend, or another backend service can send requests and receive JSON responses.

Step 3: Add a simple controller

Create a controller named ProductsController.cs inside the Controllers folder and add this code:

using Microsoft.AspNetCore.Mvc;

namespace FirstWebApi.Controllers
{
    [ApiController]
    [Route("api/[controller]")]
    public class ProductsController : ControllerBase
    {
        [HttpGet]
        public IActionResult GetProducts()
        {
            var products = new[]
            {
                new { Id = 1, Name = "Keyboard", Price = 120.00 },
                new { Id = 2, Name = "Mouse", Price = 55.00 },
                new { Id = 3, Name = "Monitor", Price = 899.00 }
            };

            return Ok(products);
        }
    }
}

Step 4: Run the application

Run the project, then open the endpoint:

/api/products

You should see a JSON response containing the sample products.

Step 5: Why this matters

This small example teaches several important ideas at once: routing, controllers, JSON output, and HTTP GET requests. These ideas form the base for more advanced APIs with databases, authentication, and validation.

Where to go next

Once you understand a basic GET endpoint, the next practical step is to build a full CRUD API connected to a real database. That is where you learn how APIs become useful in real applications.