Tutorials ASP.NET Core Web API Tutorial
Download and Install .NET Core SDK — Complete Guide
Download and Install .NET Core SDK — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of ASP.NET Core Web API Tutorial on Toolliyo Academy.
On this page
ASP.NET Core Web API Tutorial · Lesson 4 of 100
ASP.NET Core Web API Introduction
Beginner → Intermediate → Advanced → Professional
Beginner · 1 — API foundations · ~6 min · Module 1: Web API Fundamentals
What is this?
ASP.NET Core Web API is a framework on .NET for building HTTP JSON services. Program.cs configures services and middleware. Controllers (or minimal APIs) map routes to C# code. Kestrel is the web server that listens for requests.
Why should you care?
It is cross-platform (Windows, Linux, Mac), fast, and the standard choice for new .NET backends in 2025–2026. Companies migrating from .NET Framework Web API 2 use ASP.NET Core.
See it live — copy this example
Create a Web API (dotnet new webapi), paste the example, run dotnet run, test in Swagger.
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
var app = builder.Build();
app.UseSwagger();
app.UseSwaggerUI();
app.MapControllers();
app.Run();
Run Example »
This lesson uses terminal or setup steps. Run commands on your computer — the live editor appears on coding lessons.
What happened?
- CreateBuilder sets up dependency injection.
- AddControllers registers API controllers.
- MapControllers connects routes.
- Swagger gives you a test UI in development.
Try it yourself
- Create ShopNest.API with dotnet new webapi.
- Open Program.cs and read each line — match it to the diagram in this lesson.
- Add a ProductsController with one GET action.
- Change a route URL or DTO property and save — test again in Swagger or curl.
- Return the wrong status code on purpose (404 instead of 200) and see what the client shows.
Remember
Program.cs = DI + middleware pipeline + Run(). Controllers live in Controllers/ folder with [ApiController]. Swagger helps you test without writing a frontend first.