Lesson 5 of 40 Web Development Intermediate 50 min

ASP.NET Core 10 Web APIs

In this lesson, you will learn how to build modern Web APIs in ASP.NET Core 10 using Visual Studio 2026. We will cover minimal APIs, route groups, OpenAPI support, Problem Details, and performance-oriented publishing with Native AOT.

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What you will learn

How ASP.NET Core Web APIs work in Visual Studio 2026
How to organize endpoints with minimal APIs and route groups
How to expose OpenAPI documentation
How to standardize error responses with Problem Details
How Native AOT can improve deployment performance

Why this matters: Web APIs are the backbone of many modern applications. They power mobile apps, JavaScript front ends, desktop clients, cloud services, and enterprise systems.

Creating an ASP.NET Core Web API project

In Visual Studio 2026, you can create a Web API project quickly from the start window or the New Project dialog. Choose ASP.NET Core Web API, then select the appropriate .NET version and authentication options.

Open Visual Studio 2026
Click Create a new project
Select ASP.NET Core Web API
Enter the project name and location
Choose the target framework and create the project

Project Option	Purpose
OpenAPI Support	Generates API documentation automatically
Use Controllers	Useful for traditional controller-based APIs
HTTPS	Secures communication between client and server
Authentication	Adds identity and access control when needed

Part 1: Minimal APIs with Route Groups

Minimal APIs let you define endpoints directly in Program.cs. They are compact, readable, and ideal for lightweight services and modern API-first applications.

Route groups help you organize related endpoints under a common route prefix. This makes your code easier to maintain and improves consistency across endpoints.

var builder = WebApplication.CreateBuilder(args);

var app = builder.Build();

var orders = app.MapGroup("/api/orders")

  .RequireAuthorization()

  .WithOpenApi();

orders.MapGet("/{id}", async (int id, IOrderService svc) =>

  await svc.GetByIdAsync(id) is {} order

  ? Results.Ok(order)

  : Results.NotFound());

app.Run();

Tip: Route groups are especially useful when you have multiple endpoints for orders, customers, products, or users and want to keep them logically grouped together.

Part 2: Native AOT Compilation

Native AOT compiles your ASP.NET Core app into a native executable. This can improve startup speed and reduce memory usage, making it attractive for microservices and cloud-native deployments.

To enable it, add the following settings to your project file:

<!-- In your .csproj file -->

<PropertyGroup>

  <PublishAot>true</PublishAot>

  <InvariantGlobalization>true</InvariantGlobalization>

</PropertyGroup>

Native AOT is not necessary for every project, but it can be a great option when fast startup and lower resource usage are important.

Part 3: OpenAPI 3.1 with API documentation

OpenAPI support helps developers understand, test, and integrate with your API. In ASP.NET Core, you can expose documentation endpoints and interactive API references easily.

builder.Services.AddOpenApi();

app.MapOpenApi();

app.MapScalarApiReference();

// Example UI endpoint: /scalar/v1

This is useful during development, team collaboration, and external integration. Good API documentation reduces confusion and helps consumers use your endpoints correctly.

Part 4: Problem Details for consistent error handling

APIs should return errors in a predictable format. ASP.NET Core supports RFC 7807 Problem Details, which standardizes error responses for clients.

builder.Services.AddProblemDetails();

app.UseExceptionHandler(handler =>

  handler.MapProblemDetails());

This approach improves client-side debugging and makes error handling more professional and consistent.

Error Feature	Benefit
Problem Details	Consistent error payload for all clients
Exception Handler	Centralized handling of unexpected errors
Status Codes	Improves API clarity and client response handling

Best practices for ASP.NET Core APIs

Keep endpoints small and focused
Use meaningful route names and HTTP verbs
Validate input carefully before processing
Return proper status codes such as 200, 201, 400, 404, and 500
Document your endpoints clearly with OpenAPI
Use dependency injection for services and repositories
Centralize error handling for consistency

Summary

In this lesson, you learned how to build ASP.NET Core 10 Web APIs in Visual Studio 2026 using minimal APIs, route groups, OpenAPI support, Problem Details, and Native AOT. These features help you create APIs that are modern, maintainable, and ready for real-world use.

In the next lesson, you will continue with Entity Framework Core 10, where you will learn how to connect your API to a database and manage data more effectively.