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!


Discussion is closed. Login to edit/delete existing comments.

  • Bob Collins 0

    Looks very promising 

  • Bishnu Rawal 0

    Thanks team for the hard work. News of the day for me.

  • Troy Robinson 0

    Glad to hear this, was worried that the news would be that the project was scrapped!  Awesome – can’t wait for JS to slowly go away.

  • Warren R 0

    Thank you for committing to this, really looking forward to coming back to C# for web development in the years to come.

  • Jiping 0

    Awesome Blazor awesome!
    Is there a rich starter kit, like those Bootstrap Admin Template, it will boost the community.

  • Baran Ozdemir 0

    Great !!!! Congratulations, amazing work. 

  • shiva prasanth 0

    personally i feel like this is revolution, same like when nodejs introduced which lets us run javascript in both server and browser.
    there are some projects like brython(runs python(syntax) on browser) but it won’t leverage webassembly.
    blazor using webassembly really boosts performance IMO.
    very very cool.

  • Ben Hayat 0

    So Dan, what wasaccomplished or resolved in this preview that kicked Blazor out of experimental into offical product?


    • Daniel RothMicrosoft employee 0

      We’ve known for several months now that we wanted to ship Blazor based on the level of community interest and the results of our technical investigations. The main delay was to allow time to determine the roadmap for shipping Blazor. We’ve already announced that server-side Blazor will ship with .NET Core 3.0 later this year and we hope to share more details on the roadmap for the client-side WebAssembly support soon.

      • Juho Hanhimäki 0

        Hi Dan,
        Any updates on the roadmap for client-side WASM support? We’re planning to begin development on standalone client-side application and it would be greatly helpful if there was rough timeframes for RC (go live?) and GA releases?
        The current previews look very promising!

        • Daniel RothMicrosoft employee 0

          Nothing to share yet, unfortunately. Right now we’re almost entirely focuses on shipping support for Blazor Server apps in .NET Core 3.0. We have publicly announced that WebAssembly support will come with .NET 5 late next year. We’re still trying to figure out if/when we can shipping something earlier than that for folks to use.

          • Juho Hanhimäki 0

            Hopefully you can come up with some kind of interim release before the full .NET 5 release (.NET Core based WASM runtime?). Even the current previews work quite nicely and in our business the “it works” is the most important feature of a program. Finally having a Microsoft solution for client sided web development is very exciting and I think that is what has caused most of the hype behind Blazor. I feel like it would be a long wait for some of us to wait for .NET 5. 🙂

  • 王锦 0

    Thanks for your guys great jobs!
    I have one question: where is blazor library template in visual studio? or shoud i use blazorlib cli to generate blazor library project? or just use razor library project?

    • Chris Sainty 0

      The Blazor Library project is only available via the dotnet CLI templates. Whether you use a razor class library or blazor library depends on what you need. Razor class libraries will work fine with server-side Blazor but if you need to include static assets then you should continue to use a Blazor library. However, static assets still don’t work with server-side Blazor pending the resolution of Hope that makes sense.


    Wow, very nice!!! One of my best moments this year.:) You’re doing a good job 👌

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