Overview of ASP.NET Core

By Daniel Roth, Rick Anderson, and Shaun Luttin

ASP.NET Core is a cross-platform, high-performance, open-source framework for building modern, cloud-enabled, Internet-connected apps.

With ASP.NET Core, you can:

• Build web apps and services, Internet of Things (IoT) apps, and mobile backends.
• Use your favorite development tools on Windows, macOS, and Linux.
• Deploy to the cloud or on-premises.
• Run on .NET.

Why choose ASP.NET Core?

Millions of developers use or have used ASP.NET 4.x to create web apps. ASP.NET Core is a redesign of ASP.NET 4.x, including architectural changes that result in a leaner, more modular framework.

ASP.NET Core provides the following benefits:

• A unified story for building web UI and web APIs.
• Architected for testability.
• Razor Pages makes coding page-focused scenarios easier and more productive.
• Blazor lets you use C# in the browser alongside JavaScript. Share server-side and client-side app logic all written with .NET.
• Ability to develop and run on Windows, macOS, and Linux.
• Open-source and community-focused.
• Integration of modern, client-side frameworks and development workflows.
• Support for hosting Remote Procedure Call (RPC) services using gRPC.
• A cloud-ready, environment-based configuration system.
• Built-in dependency injection.
• A lightweight, high-performance, and modular HTTP request pipeline.
• Ability to host on the following:
  • Kestrel
  • IIS
  • HTTP.sys
  • Nginx
  • Docker
• Side-by-side versioning.
• Tooling that simplifies modern web development.

Build web APIs and web UI using ASP.NET Core MVC

ASP.NET Core MVC provides features to build web APIs and web apps:

• The Model-View-Controller (MVC) pattern helps make your web APIs and web apps testable.
• Razor Pages is a page-based programming model that makes building web UI easier and more productive.
• Razor markup provides a productive syntax for Razor Pages and MVC views.
• Tag Helpers enable server-side code to participate in creating and rendering HTML elements in Razor files.
• Built-in support for multiple data formats and content negotiation lets your web APIs reach a broad range of clients, including browsers and mobile devices.
• Model binding automatically maps data from HTTP requests to action method parameters.
• Model validation automatically performs client-side and server-side validation.

Client-side development

ASP.NET Core includes Blazor for building richly interactive web UI, and also integrates with other popular frontend JavaScript frameworks like Angular, React, Vue, and Bootstrap. For more information, see ASP.NET Core Blazor and related topics under Client-side development.

ASP.NET Core target frameworks

ASP.NET Core 3.x or later can only target .NET.

There are several advantages to targeting .NET, and these advantages increase with each release. Some advantages of .NET over .NET Framework include:

• Cross-platform. Runs on Windows, macOS, and Linux.
• Improved performance
• Side-by-side versioning
• New APIs
• Open source

Recommended learning path

We recommend the following sequence of tutorials for an introduction to developing ASP.NET Core apps:

1. Follow a tutorial for the app type you want to develop or maintain.

   App type	Scenario	Tutorial
   Web app	New server-side web UI development	Get started with Razor Pages
   Web app	Maintaining an MVC app	Get started with MVC
   Web app	Client-side web UI development	Get started with Blazor
   Web API	RESTful HTTP services	Create a web API†
   Remote Procedure Call app	Contract-first services using Protocol Buffers	Get started with a gRPC service
   Real-time app	Bidirectional communication between servers and connected clients	Get started with SignalR

2. Follow a tutorial that shows how to do basic data access.

   Scenario	Tutorial
   New development	Razor Pages with Entity Framework Core
   Maintaining an MVC app	MVC with Entity Framework Core

3. Read an overview of ASP.NET Core fundamentals that apply to all app types.

4. Browse the table of contents for other topics of interest.

†There's also an interactive web API tutorial. No local installation of development tools is required. The code runs in an Azure Cloud Shell in your browser, and curl is used for testing.

Migrate from .NET Framework

For a reference guide to migrating ASP.NET 4.x apps to ASP.NET Core, see Update from ASP.NET to ASP.NET Core.

How to download a sample

Many of the articles and tutorials include links to sample code.

1. Download the ASP.NET repository zip file.
2. Unzip the AspNetCore.Docs-main.zip file.
3. To access an article's sample app in the unzipped repository, use the URL in the article's sample link to help you navigate to the sample's folder. Usually, an article's sample link appears at the top of the article with the link text View or download sample code.

Preprocessor directives in sample code

To demonstrate multiple scenarios, sample apps use the #define and #if-#else/#elif-#endif preprocessor directives to selectively compile and run different sections of sample code. For those samples that make use of this approach, set the #define directive at the top of the C# files to define the symbol associated with the scenario that you want to run. Some samples require defining the symbol at the top of multiple files in order to run a scenario.

For example, the following #define symbol list indicates that four scenarios are available (one scenario per symbol). The current sample configuration runs the TemplateCode scenario:

#define TemplateCode // or LogFromMain or ExpandDefault or FilterInCode

To change the sample to run the ExpandDefault scenario, define the ExpandDefault symbol and leave the remaining symbols commented-out:

#define ExpandDefault // TemplateCode or LogFromMain or FilterInCode

For more information on using C# preprocessor directives to selectively compile sections of code, see #define (C# Reference) and #if (C# Reference).

Breaking changes and security advisories

Breaking changes and security advisories are reported on the Announcements repo. Announcements can be limited to a specific version by selecting a Label filter.

Next steps

For more information, see the following resources:

• Get started with ASP.NET Core
• Publish an ASP.NET Core app to Azure with Visual Studio
• ASP.NET Core fundamentals
• The weekly ASP.NET community standup covers the team's progress and plans. It features new blogs and third-party software.