OpenSilver: Silverlight makes an open source comeback

Martin Brinkmann
Mar 9, 2020

Ten years ago, plugins were needed for a lot of things in web browsers. Today, only Flash survived in the browser and its time is running out as well. Plugins such as Flash, Silverlight, or Java were fundamental parts of the Internet but the rise of web technologies such as JavaScript caused these to be removed from web browsers by companies such as Mozilla or Google.

Adobe will end Flash development in 2020 and Microsoft revealed that it won't support Silverlight from October 2021 anymore.

Developers and projects that use these technologies won't be able to do so anymore when support ends for these products. While it is possible to run some older versions of browsers and the last plugin released, it is not recommended due to security concerns.

Tip: Flash gamers may check out the Flash Games preservation project to continue playing games made in Flash.

Silverlight developers and projects may have a way out however. The French organization Userware released a preview of OpenSilver today, an open source implementation of Silverlight that is based on web standards and modern web technologies such as WebAssembly.

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.

Since it is no longer provided as a plugin, it is compatible with (most) modern web browsers and should run fine in those.

One component, CSHTML5 allows developers to make web apps using C# and XAML. It comes with a tool to port existing Silverlight and WPF applications to the web by "compiling C# and XAML files to HTML and JavaScript".

Interested developers may download the preview release from the OpenSilver website. A Microsoft Account is required to download the preview to the local system. Additional information is provided on the project's GitHub website.

About 60% of Silverlight APIs are currently supported. Userware plans to improve API support in the coming months and add support for Open RIA Services, AOT compilation and third-party libraries. Ahead of Time (AOT) compilation will speed up loading times by "at least 30 times" when it lands.

The company launched a conversion service to convert existing Silverlight applications to the modern version so that it may run on websites without plugin requirement.

Interested users may load the demo from here to check out the functionality that is currently available.

Now You: Have you used Silverlight in the past? What is your take on the resurrection?

OpenSilver: Silverlight makes an open source comeback
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OpenSilver: Silverlight makes an open source comeback
OpenSilver is an open source project that aims to resurrect Silverlight using web standards and modern web technologies such as WebAssembly.
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  1. Vasil Buraliev said on July 26, 2023 at 11:34 am

    Hi all,

    Upon reviewing the comments pertaining to XAML and references to the UNO Platform, it is evident that Silverlight has become less prevalent in the current web market. An observation can be made regarding the primary distinction between UNO and OpenSilver, where UNO renders content within Canvas, while OpenSilver incorporates HTML into the DOM of a web page.

    In the past, Silverlight emerged as a commendable technology; although fewer websites have been based on it in recent years, numerous business applications still rely on Silverlight in 2023. These applications represent substantial investments made by prominent enterprises to support critical business processes. The emergence of OpenSilver ( offers these businesses and similar entities an opportunity to migrate their solutions from Silverlight to OpenSilver, enabling seamless operation within modern browsers, free from the need for any plugins.

    Additionally, I would like to bring to your attention another noteworthy development. Several years after OpenSilver’s initial release, a solution known as “XAML for Blazor” ( has emerged, built upon the OpenSilver framework. This solution facilitates the utilization of XAML in modern Blazor WebAssembly applications, further expanding the possibilities for developers in leveraging this technology.

  2. Peter Newton said on March 18, 2020 at 8:56 pm

    May the Linux God forgive and protect ye, from all of your wicked Windows ways my child !

    I pray that ye shall receive the blessing of the great Tux, The Penguin, and ye miss-spent
    Microshaft/Papple past will dissolve into emptiness, to be replaced with genuine knowledge
    and wisdom.

    May Tux bless you, in the name of the beak, the webbed foot, and the flipper, ah-kernel 5.4.

    Peter Newton [London UK]

  3. Dan Biebe said on March 11, 2020 at 3:54 pm

    Hold on, isn’t this what Uno Platform has been doing all along – – essentially C# and XAML on the desktop, mobile and web – also using WebAssembly

  4. Anonymous said on March 11, 2020 at 10:06 am

    I commented on Silverlight and the problem with WebAssembly two days ago, but this never appeared. I saw that the anti-IH bashing session was removed from comments too and I can understand that, but my comment had nothing to do with that.

  5. clake said on March 11, 2020 at 1:49 am

    I used it for Netflix too, on winXP with older browsers from 2014 – 16. Netflix is all html5 now, with widevine for drm.

  6. Graham said on March 10, 2020 at 7:38 am

    The only website I ever used Silverlight for was Netflix. Do they still use that, or have they moved on? I mainly just watch Netflix on my TV nowadays, so I’m not sure.

  7. Anonymous said on March 10, 2020 at 3:47 am

    From the start till the end of Silverlight I never use it. It’s not required or even mentioned on all website I visited. I only found out about Silverlight because some news site mentioned it. I wonder if it really exists?

  8. ULBoom said on March 10, 2020 at 1:36 am

    I never knew what Silverlight did, still don’t. Just one of those periodically deleted things that reappeared with updates, like Google Earth. Present or not, didn’t seem to make any difference in browsing.

    The name is cool.

    Today we have Widevine and Open H264, neither of which seem to do anything off or on beside collect data, so off they go.

  9. Peter Newton said on March 10, 2020 at 1:12 am

    Oh My God !

    Silverlight ? !!

    Not this crap !! again ?? …… thank GOD I switched to Linux !!

    Peter Newton [London UK]

    1. London's Burning said on March 16, 2020 at 4:25 am

      @Peter Newton

      God helped you switch to Linux?

      Please give more details about this religious experience, as I’m writing a related book:

      The Linux Devotee’s Bible of Religious Crazy Talk

  10. Yuliya said on March 9, 2020 at 10:16 pm

    Never used it, (probably; most likely) never will. But good on Microsoft for making it open source.

  11. Anonymous said on March 9, 2020 at 7:37 pm

    I hated Silverlight. It hijacked my webcam and spied on me. It hasn’t been on my Windows computer for years.

  12. allen said on March 9, 2020 at 6:37 pm

    XAML makes me like it. .NET makes me not like it so much.

    What’s the real purpose here? …simply migrating from current Silverlight implementations? I think it may be too late for that except for those who had no plan for moving forward (and were just waiting for the end).

  13. rip said on March 9, 2020 at 6:27 pm

    Unfortunately, one site I have to use (government) must have SL. This is the only reason I ever fire up IE. I do this from a Windows VM in case the nasties come knocking.

    I also can’t do any web automation on this site since I don’t know how or want to know how to debug SL apps. UGLY!

  14. Gerard said on March 9, 2020 at 6:23 pm

    I wonder what the rationale behind this project is. Do we need Sliverlight mark 2, aka OpenSilver? Not in my humble opinion.
    “It uses Mono for WebAssembly and Microsoft Blazor.”
    Is it for MS Windows only? That would make sense, for that OS doesn’t have enough flaws and vulnerabilities :-)

    1. foolishgrunt said on March 9, 2020 at 7:43 pm

      I would assume it’s primarily for archival purposes, to allow people using modern web browsers to access legacy projects that were built for Silverlight. Similar to Mozilla’s (discontinued) Shumway project for Flash.

  15. Addy T. said on March 9, 2020 at 6:04 pm

    Silverlight never took off. This project is somewhat interesting, but I do personally believe websites should be kept simple and devoid of eyecandy. There may be a number of serious ways to employ this project, so I am not opposed to it.

  16. Jeff said on March 9, 2020 at 3:28 pm

    The web needs more animation so why the hell not?

    1. Addy T. said on March 9, 2020 at 6:01 pm

      I disagree. The web needs less content that puts stress on your CPU and RAM. It is already a freakshow full of bloat.

      1. Jeff said on March 12, 2020 at 9:14 am

        Freakshow of bloat is due to Javascript and ads. If you know how to block HTML5 video autoplay and Javascript wreaking havoc with your pages, then you are ahead of the curve. Simple animation has got nothing to do with it.

      2. Niall said on March 10, 2020 at 10:14 am

        I think it was sarcasm

    2. Jeff said on March 9, 2020 at 3:29 pm

      Especially if it’s without plugins and using open technologies

  17. Nico Weytens said on March 9, 2020 at 3:22 pm

    Out of curiosity, which (popular) webservice requires Silverlight. I haven’t had SL on my PC since years and haven’t notice sites needing it…

    I know it was required for the SCOM webconsole and SCCM App Portal. If you installed an sccm client silverlight used to be installed as well, but I think that’s no longer the case in recent versions.

    1. who cares said on March 16, 2020 at 4:39 am

      @Nico Weytens

      Silverlight is pretty much dead, with it’s final release in 2019.

      Microsoft was or will likely the last to require it, with their tutorial videos and such. was the last non-Microsoft site I know of that required Silverlight to play the video.

    2. matthiew said on March 11, 2020 at 8:56 am

      Netflix used to require Silverlight for resolutions above 720p.

  18. Anonymous said on March 9, 2020 at 10:01 pm

    I would gladly laugh with you all if your attacks were directed at Brave for being an adware browser, instead of just being attacks from a competing adware browser. Collectively, your shilling is much more vocal than his. Now that you ended the debate on who has the biggest browser with your final blows, say hi for me to Cliqz, Pocket, Google, Cloudflare, Leanplum, Adjust, the newly invited Adzerk (I love the name already), and all the rest of the big Mozprivacy family.

  19. Anonymous said on March 9, 2020 at 9:29 pm

    Sure, the Microsoft plugin is much less of a threat if they are no longer in control of what it can do at worst. But there is another beast that is awakening and that it uses, WebAssembly. Welcome receiving already compiled code to execute in your browser ! Goodbye freedom to control it.

  20. Nico Weytens said on March 9, 2020 at 7:16 pm

    You sound like an advert for Brave :-p

  21. Hunter said on March 9, 2020 at 6:23 pm

    This article had absolutely nothing to do with Brave in particular, and yet you felt the need to shoehorn it into your comment anyway.

    And you wonder why people call you a Brave shill.

  22. Iron Heart said on March 9, 2020 at 9:18 pm

    @All posters replying to @Nico Weytens:

    This is a troll impersonating me, I think this is very obvious. My comments are more balanced than that, and do not tend to apply silly hyperbole. This reply is from the Fake Iron Heart troll:

    @thebrowser, hopefully you still find it “hilarious” the moment someone starts impersonating you. I think you only find it funny as long as you aren’t the target, as always. Pathetic.

  23. Inigo Montoya said on March 9, 2020 at 8:17 pm


  24. seeprime said on March 9, 2020 at 7:53 pm

    Hunter: I’m pretty sure he knows why he’s called a Brave shill.

  25. thebrowser said on March 9, 2020 at 7:17 pm

    Apparently there’s someone impersonating Iron Heart based on previous posts… But honestly it’s hilarious and hope it puts an end to this silly ‘who has the biggest browser’ that’s been going on lately here.

    Maybe it really is the original Iron Heart, though, in which case I really hope that he’s getting paid well for his services.

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