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Overview of ASP.NET Core

  • Article

By Daniel Roth, Rick Anderson, and Shaun Luttin

Note

This isn't the latest version of this article. For the current release, see the .NET 8 version of this article.

Warning

This version of ASP.NET Core is no longer supported. For more information, see .NET and .NET Core Support Policy. For the current release, see the .NET 8 version of this article.

Important

This information relates to a pre-release product that may be substantially modified before it's commercially released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

For the current release, see the .NET 8 version of this article.

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:

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

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

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

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.

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:

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, with architectural changes that result in a leaner, more modular framework.

ASP.NET Core provides the following benefits:

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

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

Client-side development

ASP.NET Core integrates seamlessly with popular client-side frameworks and libraries, including Blazor, Angular, React, Vue, and Bootstrap. For more information, see ASP.NET Core Blazor and related topics under Client-side development.

ASP.NET Core targeting .NET Framework

ASP.NET Core 2.x can target .NET Core or .NET Framework. ASP.NET Core apps targeting .NET Framework aren't cross-platform—they run on Windows only. Generally, ASP.NET Core 2.x is made up of .NET Standard libraries. Libraries written with .NET Standard 2.0 run on any .NET platform that implements .NET Standard 2.0.

ASP.NET Core 2.x is supported on .NET Framework versions that implement .NET Standard 2.0:

  • .NET Framework latest version is recommended.
  • .NET Framework 4.6.1 or later.

ASP.NET Core 3.0 or later only run on .NET Core. For more details regarding this change, see A first look at changes coming in ASP.NET Core 3.0.

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

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

To help close the API gap from .NET Framework to .NET Core, the Windows Compatibility Pack made thousands of Windows-only APIs available in .NET Core. These APIs weren't available in .NET Core 1.x.

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

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

    App type Scenario Tutorial
    Web app For new development Get started with Razor Pages
    Web app For maintaining an MVC app Get started with MVC
    Web API Create a web API†
    Real-time app Get started with SignalR

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

    Scenario Tutorial
    For new development Razor Pages with Entity Framework Core
    For 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 a web API tutorial that you follow entirely in the browser, no local IDE installation required. The code runs in an Azure Cloud Shell, and curl is used for testing.

Migrate from .NET Framework

For a reference guide to migrating ASP.NET 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: