March 9, 2020

Today we are introducing OpenSilver, an open-source reimplementation of Silverlight that runs on current browsers via WebAssembly!



Microsoft Silverlight allows to build Rich Internet Applications using C#, XAML, and .NET. However, it requires users to install a plugin. Since most browsers stopped supporting plugins a few years ago, Silverlight applications no longer work on browsers other than Internet Explorer. Furthermore, Microsoft has announced that it may stop supporting Silverlight after 2021.

What is OpenSilver

OpenSilver is a modern, plugin-free, open-source reimplementation of Silverlight, that runs on current browsers via WebAssembly. It uses Mono for WebAssembly and Microsoft Blazor. It brings back the power of C#, XAML, and .NET to client-side Web development.

The technology can be used in two ways: to create new apps and to modernize existing Silverlight applications.


OpenSilver applications are compatible with all browsers that support WebAssembly, which include all major browsers (Edge, Chrome, Firefox, Safari...) on all major platforms (Windows, macOS, iOS, Android, Linux, ChromeOS...).

When an application is compiled using OpenSilver, it runs on all those browsers without requiring users to install a plugin.

Existing Silverlight applications need to be recompiled with OpenSilver in order to run on those browsers.

How to test it

You can see an example of application here.

To build your own application, simply download the free extension for Microsoft Visual Studio 2019 (OpenSilver.VSIX), which installs the Project Templates to the "New Project" dialog.

When creating a new OpenSilver project with Visual Studio, you can choose between the Silverlight and the UWP dialects of XAML.

Migrating an existing Silverlight application to OpenSilver

To migrate an existing Silverlight application, simply recompile its source code using OpenSilver. To do so, download and install the OpenSilver extension. Then, create a new project of type "OpenSilver", copy/paste your Silverlight code into that new project, and compile it.

Compilation errors are initially expected because some features are not supported (read below), but you can work around those limitations, for example by importing a .NET Standard library or a JavaScript library. Once compiled, your application will run on all browsers without requiring users to install a plugin.

A "Silverlight Migration Support Plan" is available, which includes support and assistance to quickly get up and running.

Some of the benefits of migrating using OpenSilver include a much lower total cost, the ability to reuse the current skills of your team, greater knowledge of the code by your team, greater efficiency after migration, and fewer risks of writing new bugs because the original code has already been tested and its bugs are already known.

The management team will also save a lot of time and effort because there won't be the need to write functional nor technical specifications for the migrated application, nor to make countless meetings in case of outsourced development with a different technology.

Professional Migration Services

Userware - the company behind OpenSilver - also provides professional services to migrate entire applications from beginning to end.

To get a quote for a turn-key migration by Userware, simply contact:

You can also upload a XAP file (the Silverlight application executable) to quickly receive a quote. To do so, visit the Upload XAP page.


OpenSilver (Technology Preview) currently covers around 60% of the Silverlight API, with the most common features already supported.

Features expected in 2020 include support for Open RIA Services and Telerik UI for Silverlight (note: a license from Telerik will be required).

OpenSilver will also be updated in sync with the latest Blazor and Mono for WebAssembly projects.

One of the main improvements by the Mono for WebAssembly team expected in 2020 will be the support for Ahead-of-Time (AOT) compilation which, according to our tests, will accelerate performance by at least 30 times.

Please stay tuned at for updates.


About us:

Our company Userware was founded in 2007 in Paris, France, by two experts in Microsoft technologies. It now has a portfolio of products with more than 25,000 customers in over 75 countries.

Our team is made of .NET developers who believe that Silverlight was the best platform ever for developing line-of-business (LOB) rich internet applications (RIA). We are sad to see Silverlight die due to the lack of support for plugins in modern browsers, so we want to save it by reimplementing it using modern, open, and standards-based technologies.

We have been working very diligently for the past 6 years on CSHTML5, a Visual Studio extension that compiles C#, XAML into HTML, JavaScript. We have been able to reuse most of the CSHTML5 code to deliver OpenSilver very quickly, replacing JavaScript with WebAssembly for native execution and improved .NET compatibility.

We are now working to make OpenSilver as good as Silverlight, and we want to make it even better, so that developers have the tools to build amazing products that can change the world.



OpenSilver wouldn't be possible without the amazing work by the incredibly talented people in the Mono for WebAssembly and Blazor teams at Microsoft.



Please click here to contact us.


Press Room:

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