Today I’m excited to announce a new experimental project from the ASP.NET team called Blazor. Blazor is an experimental web UI framework based on C#, Razor, and HTML that runs in the browser via WebAssembly. Blazor promises to greatly simplify the task of building fast and beautiful single-page applications that run in any browser. It does this by enabling developers to write .NET-based web apps that run client-side in web browsers using open web standards.

If you already use .NET, this completes the picture: you’ll be able to use your skills for browser-based development in addition to existing scenarios for server and cloud-based services, native mobile/desktop apps, and games. If you don’t yet use .NET, our hope is that the productivity and simplicity benefits of Blazor will be compelling enough that you will try it.

Why use .NET for browser apps?

Web development has improved in many ways over the years but building modern web applications still poses challenges. Using .NET in the browser offers many advantages that can help make web development easier and more productive:

• Stable and consistent: .NET offers standard APIs, tools, and build infrastructure across all .NET platforms that are stable, feature rich, and easy to use.
• Modern innovative languages: .NET languages like C# and F# make programming a joy and keep getting better with innovative new language features.
• Industry leading tools: The Visual Studio product family provides a great .NET development experience on Windows, Linux, and macOS.
• Fast and scalable: .NET has a long history of performance, reliability, and security for web development on the server. Using .NET as a full-stack solution makes it easier to build fast, reliable and secure applications.

Browser + Razor = Blazor!

Blazor is based on existing web technologies like HTML and CSS, but you use C# and Razor syntax instead of JavaScript to build composable web UI. Note that it is not a way of deploying existing UWP or Xamarin mobile apps in the browser. To see what this looks like in action, check out Steve Sanderson’s prototype demo at NDC Oslo last year or his prototype demo for the ASP.NET Community Standup. You can also try out a simple live Blazor app running as a static site.

Blazor will have all the features of a modern web framework including:

• A component model for building composable UI
• Routing
• Layouts
• Forms and validation
• Dependency injection
• JavaScript interop
• Live reloading in the browser during development
• Server-side rendering
• Full .NET debugging both in browsers and in the IDE
• Rich IntelliSense and tooling
• Ability to run on older (non-WebAssembly) browsers via asm.js
• Publishing and app size trimming

WebAssembly changes the Web

Running .NET in the browser is made possible by WebAssembly, a new web standard for a “portable, size- and load-time-efficient format suitable for compilation to the web.” WebAssembly enables fundamentally new ways to write web apps. Code compiled to WebAssembly can run in any browser at native speeds. This is the foundational piece needed to build a .NET runtime that can run in the browser. No plugins or transpilation needed. You run normal .NET assemblies in the browser using a WebAssembly based .NET runtime.

Last August, our friends on Microsoft’s Xamarin team announced their plans to bring a .NET runtime (Mono) to the web using WebAssembly and have been making steady progress. The Blazor project builds on their work to create a rich client-side single page application framework written in .NET.

A new experiment

While we are excited about the promise Blazor holds, it’s an experimental project, not a committed product. During this experimental phase, we expect to engage deeply with early Blazor adopters to hear your feedback and suggestions. This time allows us to resolve technical issues associated with running .NET in the browser and to ensure we can build something that developers love and can be productive with.

Where it’s happening

The Blazor repo is now public and is where you can find all the action. It’s a fully open source project: you can see all the development work and issue tracking in the public repo.

Please note that we are very early in this project. There aren’t any installers or project templates yet and many planned features aren’t yet implemented. Even the parts that are already implemented aren’t yet optimized for minimal payload size. If you’re keen, you can clone the repo, build it, and run the tests, but only the most intrepid pioneers would attempt to write app code with it today. If you are that intrepid pioneer, please do dig into the sources. Feedback and suggestions can be provided through the Blazor repo issue tracker. In the months ahead, we hope to publish pre-alpha project templates and tooling that will let a wider audience try it out.

Please also check out the Blazor FAQ to learn more about the project.

Thanks!