Build Your First .NET 10 Web API with Swagger in C# | Visual Studio 2026 (Step-by-Step)

Learn how to build your first Web API in C# using .NET 10, ASP.NET Core, and Visual Studio 2026, and configure Swagger (OpenAPI) for testing and documentation. This beginner-friendly tutorial will guide you step by step, from project creation to running and verifying your API endpoints in Swagger UI.

We’ll make sure you understand all the essentials of Web API development in C#, and get you started on your backend development journey! 🚀

What is a Web API?

A Web API is an interface that allows clients to communicate with your application over HTTP.
Web APIs can be consumed by web apps, mobile apps, or other services, and return data in formats like JSON.
ASP.NET Core makes it easy to create scalable and maintainable Web APIs using C#, and .NET 10 provides modern features and performance improvements.

Why Swagger (OpenAPI)?

Swagger (OpenAPI) is a tool that:

Automatically generates API documentation

Provides a UI to test endpoints

Helps developers understand request and response formats
In this tutorial, we’ll manually configure Swagger and troubleshoot common issues like 404 errors to make sure your API works perfectly.

What Will You Learn in This Tutorial?

By the end of this video, you will be able to:

Create a new ASP.NET Core Web API project in Visual Studio 2026 (.NET 10)

Understand the project structure of a .NET 10 Web API

Configure Swagger manually and verify it works in your project

Write your first API controller in C#

Run the Web API using F5 in Visual Studio 2026

Test your API endpoints in Swagger UI

Understand HTTP response status codes (like 400)

Troubleshoot common issues such as Swagger 404 errors

Configure launchSettings.json for Swagger

Chapters:
0:00 Introduction of build a web api using .net 10 & Visual Studio 2026
00:26 What we will build in the video
00:49 Create a new project
02:01 Troubleshooting of Swagger 404 error
02:28 Install Swagger Packages
03:06 Install Swagger Packages using CLI
04:13 Register Swagger Services
04:44 Enable Swagger Middleware
05:35 Run and verify swagger UI
06:14 Difference between UseSwagger and UseSwaggerUI methods
07:56 About comment lines in .NET
08:38 Project structure of ASP.NET Core Web API
10:33 Create a controller and explained about it
12:00 A sample of response status is 400
13:41 Run and verify new endpoint in Swagger
14:24 Configure Swagger in launchSettings.json
15:17 Recap

Web API – Quick Q&A

Q1: What is a Web API?
A: A Web API is a backend service that allows clients (like web apps or mobile apps) to send requests and receive responses over HTTP, typically in JSON format.

Q2: What is Swagger and why do we use it?
A: Swagger (OpenAPI) generates interactive API documentation and allows you to test your endpoints directly in a browser.

Q3: What is the difference between UseSwagger() and UseSwaggerUI()?

UseSwagger() – Registers the Swagger generator middleware that generates the Swagger specification.

UseSwaggerUI() – Registers the Swagger UI middleware to display a web page for testing your API endpoints.

Q4: How do I test my API?
A: You can test API endpoints using:

Swagger UI – interactive testing interface

Postman – manual HTTP requests

C# HttpClient – programmatically test endpoints in your code

Q5: Who is this tutorial for?

Beginners learning C# Web APIs

Students and fresh graduates starting backend development

Developers new to ASP.NET Core or .NET 10

.NET developers upgrading to .NET 10

If you haven’t installed .NET 10 yet, check out our previous tutorial here:
Install .NET 10 and Visual Studio 2026: https://youtu.be/RkZx6oin-yQ

This beginner-friendly tutorial covers:

Creating a new ASP.NET Core Web API project

Understanding the .NET 10 project structure

Configuring Swagger manually

Writing your first API controller in C#

Running the Web API using Visual Studio (F5)

Testing your API using Swagger UI

This tutorial is perfect for:

Beginners learning C#

Students and fresh graduates

Developers new to Web APIs

.NET developers upgrading to .NET 10

#dotnet10 #csharp #webapi #aspnetcore #swagger #visualstudio2026 #backenddevelopment #muthudevhub

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Видео Build Your First .NET 10 Web API with Swagger in C# | Visual Studio 2026 (Step-by-Step) канала Muthu Dev Hub