Create & Deploy Your First ASP.NET Core 8 Web API (Beginner’s Guide)

If you want to learn backend development in 2025, there’s one framework you shouldn’t overlook: ASP.NET Core 8. It’s fast, scalable, open-source, and backed by Microsoft. Whether you’re going to build APIs for enterprise apps or just experimenting with hobby projects, ASP.NET Core gives you the power to build modern web services — with performance that rivals Node.js and Go.

But let’s face it — most beginner tutorials stop at “Hello World” or echo boilerplate from Microsoft Docs.
At DebugBoat, we’re going beyond that.

In this hands-on guide, you won’t just create a web API — you’ll build, test, and deploy a working Book API using ASP.NET Core 8’s Minimal API style.

You will learn,

What Is a Web API?
Understand how the new .NET 8 structure works
Create Your ASP.NET Core 8 Minimal API Project
Deploy your app live — for free — using Azure App Service

By the end, you’ll have a working backend app, visible on the internet, and the confidence to build more.

We will build a simple, practical and lightweight Book API with the following features:

GET /books : To fetch the list of books
POST /books : To add new books

So, lets start with,

What Is a Web API?

Web API stands for Web Application Programming Interface which makes possible two applications to talk to each other using the internet.

You can imagine Web API as an waiter in a restaurant. We go through the menu, select one or more items and ask the waiter for the same. The waiter takes that order, goes to the kitchen area and tells the chef to prepare the food we have requested. Then the waiter returns with the food we have ordered.

Understanding the New .NET 8 Structure

.NET 8 makes it quicker and easier to build web APIs, especially for smaller projects, by using a simpler style called Minimal APIs.

In older versions (.NET 5 or 6), you’d see a Startup.cs file, a more complex folder structure, and lots of boilerplate. But in .NET 8, with Minimal APIs:

There’s no Startup.cs
Everything is wired inside a single file — Program.cs
The code is cleaner and more readable for beginners

Project Structure Breakdown

When we run,

dotnet new webapi -n BookApi

It will create the following file structure

BookApi/
├── Controllers/       (May not be used in Minimal APIs)
├── Program.cs         -> The entry point
├── Properties/
├── Book.cs            -> Your model (you’ll create this)
├── BookApi.csproj     -> Project file
└── appSettings.json   -> Configurations

Now lets discuss on the most important parts

Program.cs – Which is responsible for everything

This file does the following,

App configuration
Routing
Dependency injection
Middleware (like CORS, Swagger) [We will discuss on this later]

Programs.cs file looks like this

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => "Hello, DebugBoat!");

app.Run();

Isn’t it simple?

The next is appSettings.json

appSettings.json

This is where you define your app configuration like database connection strings, logging levels and more. For a sample, you can consider this,

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*"
}

Now the Project file,

BookApi.csproj

Ideally the we don’t edit this manually unless we add libraries or change the framework. The csproj or Project file consists the following details,

What SDK you’re using (<TargetFramework>net8.0</TargetFramework>)
Any NuGet packages being used
Build settings of the project

These are all the mandatory files required to run the project. Apart from these, class files are added with .cs extension as per requirement. For example,

RegisterUser.cs
AddBooks.cs

Okay, now we have understood the overall project architecture, lets create a simple example to get some hands-on

Create Your ASP.NET Core 8 Minimal API Project

We will be creating a Web API project – Book API

Please ensure that you have,

.NET SDK Installed – Jut open Command Prompt/Power Shell/Terminal and type dotnet --info
Visual Studio Code

If you have, just follow the steps below:

Open your terminal (Command Prompt, PowerShell, or Bash)

dotnet new webapi -n BookApi
cd BookApi
code .

A new ASP.NET Core 8 Web API project will be created in a folder named BookApi and the same will be opened in Visual Studio Code.

Now run the app using the following command,

dotnet run

Keep eye on your output window and you will be seeing this,

Now listening on: https://localhost:5001
Application started. Press Ctrl+C to shut down.

Now open any browser and type this URL,

https://localhost:5001/swagger

Great. So, now you have created your first .NET Web API project and you are able to run it. Next step is to deploy it on the cloud with the help of Azure App Services. Sounds interesting? Let’s dive in.

Deploying ASP.NET Core 8 API to Azure App Service

Here we will use the Azure Free F1 tier. If you face any problem regarding the Azure Subscription, put the same in the comment and I will try to sort it out.

We will use the Azure App Service. Wondering what is it?

Azure App Service is a PaaS (Platform as a Service) offering from Microsoft that lets you:

Host web APIs and apps in the cloud
Deploy directly from Visual Studio Code or GitHub
Get a public HTTPS URL for your app instantly

There is one Extension for Visual Studio Code which makes it easier to deploy your app. Let’s go step by step.

Step 1: Install the Azure App Service Extension

Open Visual Studio
Go to the Extensions tab
Search: “Azure App Service”
Click Install

Similarly install Azure Account and C# for Visual Studio Code

Step 2: Sign In to Azure

Click on the Azure icon in the sidebar → Sign In and follow the instructions

Step 3: Deploy Your App

Open your BookApi project in VS Code
Right-click the project folder → Deploy to Web App
Follow the prompts:

Create a new Web App
Choose a unique name: debugboat-bookapi
Select runtime: .NET 8 (LTS)
Choose region (closest to you)
Select Free F1 tier

VS Code will automatically build and publish your app to Azure.

Step 4: Open Your Live API

After deployment, your app will be live at:

https://<your-app-name>.azurewebsites.net/swagger

Now your Book API Project has been deployed to Azure App Service, you can access the swagger link and test the endpoints