Blazor now in official preview!

Daniel Roth

With this newest Blazor release we’re pleased to announce that Blazor is now in official preview! Blazor is no longer experimental and we are committing to ship it as a supported web UI framework including support for running client-side in the browser on WebAssembly.

A little over a year ago we started the Blazor experimental project with the goal of building a client web UI framework based on .NET and WebAssembly. At the time Blazor was little more than a prototype and there were lots of open questions about the viability of running .NET in the browser. Since then we’ve shipped nine experimental Blazor releases addressing a variety of concerns including component model, data binding, event handling, routing, layouts, app size, hosting models, debugging, and tooling. We’re now at the point where we think Blazor is ready to take its next step.

Blazor icon

Simplifying the naming and versioning

For a while, we’ve used the terminology Razor Components in some cases, and Blazor in other cases. This has proven to be confusing, so following a lot of community feedback, we’ve decided to drop the name ASP.NET Core Razor Components, and return to the name Server-side Blazor instead.

This emphasizes that Blazor is a single client app model with multiple hosting models:

  • Server-side Blazor runs on the server via SignalR
  • Client-side Blazor runs client-side on WebAssembly

… but either way, it’s the same programming model. The same Blazor components can be hosted in both environments.

Also, since Blazor is now part of .NET Core, the client-side Blazor package versions now align with the .NET Core 3.0 versions. For example, the version number of all the preview packages we are shipping today is 3.0.0-preview4-19216-03. We no longer use separate 0.x version numbers for client-side Blazor packages.

What will ship when

  • Server-side Blazor will ship as part of .NET Core 3.0. This was already announced last October.
  • Client-side Blazor won’t ship as part of the initial .NET Core 3.0 release, but we are now announcing it is committed to ship as part of a future .NET Core release (and hence is no longer an “experiment”).

With each preview release of .NET Core 3.0, we will continue to ship preview releases of both server and client-side Blazor.

Today’s preview release

New features in this preview release:

  • Templates updated to use the .razor file extension
  • _Imports.razor
  • Scope components with @using
  • New component item template
  • New Blazor icons
  • Blazor support in Visual Studio Code

Check out the ASP.NET Core 3.0 Preview 4 announcement for details on these improvements. See also the Blazor release notes for additional details on this preview release.

Get the Blazor preview

To get started with the Blazor preview install the following:

  1. .NET Core 3.0 Preview 4 SDK (3.0.100-preview4-011223)
  2. The Blazor templates on the command-line:

    dotnet new -i Microsoft.AspNetCore.Blazor.Templates::3.0.0-preview4-19216-03
  3. Visual Studio 2019 Preview with the ASP.NET and web development workload selected as well as the latest Blazor extension from the Visual Studio Marketplace, or Visual Studio Code with the latest C# extension (now with Blazor support!).

You can find getting started instructions, docs, and tutorials for Blazor at our new Blazor home page at

Blazor home page

Upgrade to the Blazor preview:

To upgrade your existing Blazor apps to the new Blazor preview first make sure you’ve installed the prerequisites listed above then follow these steps:

  • Update all Microsoft.AspNetCore.Blazor.* package references to 3.0.0-preview4-19216-03.
  • Remove any package reference to Microsoft.AspNetCore.Components.Server.
  • Remove any DotNetCliToolReference to Microsoft.AspNetCore.Blazor.Cli and replace with a package reference to Microsoft.AspNetCore.Blazor.DevServer.
  • In client Blazor projects remove the <RunCommand>dotnet</RunCommand> and <RunArguments>blazor serve</RunArguments> properties.
  • In client Blazor projects add the <RazorLangVersion>3.0</RazorLangVersion> property.
  • Rename all _ViewImports.cshtml files to _Imports.razor.
  • Rename all remaining .cshtml files to .razor.
  • Rename components.webassembly.js to blazor.webassembly.js
  • Remove any use of the Microsoft.AspNetCore.Components.Services namespace and replace with Microsoft.AspNetCore.Components as required.
  • Update server projects to use endpoint routing:
// Replace this:
app.UseMvc(routes =>
    routes.MapRoute(name: "default", template: "{controller}/{action}/{id?}");

// With this:

app.UseEndpoints(routes =>
  • Run dotnet clean on the solution to clear out old Razor declarations.

Blazor community page is now Awesome Blazor

As part of updating the Blazor site, we’ve decided to retire the Blazor community page and instead direct folks to the community driven Awesome Blazor site. Thank you Adrien Torris for maintaining this truly “awesome” list of Blazor resources!

Try out preview Blazor UI offerings from Telerik, DevExpress, and Syncfusion

Blazor benefits from an active and supportive community that has contributed all sorts of sample apps, components, and libraries to the Blazor ecosystem. Recently popular component vendors like Telerik, DevExpress, and Syncfusion have joined in the fun and shipped previews of Blazor UI components. We encourage you to give these Blazor UI offerings a try and let them know what you think.

Give feedback

We hope you enjoy this latest preview release of Blazor. As with previous releases, your feedback is important to us. If you run into issues or have questions while trying out Blazor, file issues on GitHub. You can also chat with us and the Blazor community on Gitter if you get stuck or to share how Blazor is working for you. After you’ve tried out Blazor for a while please let us know what you think by taking our in-product survey. Click the survey link shown on the app home page when running one of the Blazor project templates:

Blazor survey

Thanks for trying out Blazor!


Comments are closed. Login to edit/delete your existing comments

  • Danish Jafri

    Thank you for all the effort! This is going to be an awesome adventure.

  • Anderson Moscarelli

    I have a client server blazor project and these properties <RunCommand>dotnet</RunCommand> and <RunArguments>blazor serve</RunArguments> , <RazorLangVersion>3.0</RazorLangVersion> are not present in anyware and i have no clue where to put <RazorLangVersion>3.0</RazorLangVersion>  . Can you advice?

    • Daniel RothMicrosoft employee

      The RazorLangVersion property should be added in a PropertyGroup in your client csproj file. You should also remove the RunCommand and RunArguments properties from your client csproj file if you have them.

  • remi bourgarel

    If you want to rename all your project file, user the following powershell

    Get-ChildItem -Path . -Filter *.cshtml -Recurse | Rename-Item -NewName{[System.IO.Path]::ChangeExtension($_.Name, “.razor”)}

  • Ross Jempson

    This sounds like Silverlight without a plugin?  When strategy changes, and resources have been prioritised for other things, and the project is retired by Microsoft, is it likely to become a community open source project.  In other words, if someone was to invest time learning this framework and build production software upon it, is there any chance that will backfire?

    • Daniel RothMicrosoft employee

      Blazor is .NET in the browser without any plugins or code transpilation; just open web standards. It’s already an open source, community driven project that is part of the .NET Foundation. So, if Microsoft decides to move onto something else, the community can always take up the reigns and keep it going. 

  • Evaldas Jocys

    Good effort. Problem is that downloading NuGet packages and providing examples which can’t simply run in the browser will result in many developers just ignoring this technology. Running C# in web browser must be simple as running single Example.html file from the local disks:
    <html><head>    <script type=”text/csharp”>        void Add(x, y)        {            var value = x + y;            document.getElementById(“Result”).value = value;        }    </script></head><body>    <input type=”text” id=”Result” />    <button onclick=”Add(1, 2)”>Calculate</button></body></html>

    • Daniel RothMicrosoft employee

      We are working hard to make the getting started experience with Blazor as simple as possible. While we’d love for .NET and C# to have a more native experience in the browser like JavaScript enjoys, we are limited by what browsers support today. Blazor is more comparable to existing frontend UI frameworks like Angular, React, or Vue. These frameworks have rich component models and include more machinery for building large scale applications.

  • thiyagu Raj

    Awesome MS ,, i am following webassembly last 6 years when it was announced and MS pickup and finally its ready , waiting to code a browser behaviors in c#,, 

  • Ma, Chuanshan

    Do we still need 10s to load a hello world demo in latest release?

  • Frank Thomas

    I agree, it does look promising. I think my main question is how does it compare to the likes of Angular and React, or is there a comparison?

  • Agustin Silva

    We are  loving blazor. Thanks.  After the update we are getting lots of errors:
    The type or namespace name ‘Mvc’ does not exist in the namespace ‘Microsoft.AspNetCore’ , any suggestions?