Installing Uno as a PWA with WebAssembly

One of the things that I don’t like about the web is that I have to access everything via the browser. Whilst favourites and bookmarks are all well and good, one of the nice things about apps is that I can do things like pin to start/taskbar (Windows) or add to homescreen (Android). Sure I can pin a website, but this leads me to my next point – it still feels like the web, rather than an app experience. There’s still the browser chrome that sits around the edge and it doesn’t feel the same as being in an app. In this post we’re going to look at one aspect of Progressive Web Applications (PWA) which is the ability to “install” the application in order to address some of my feelings towards web applications.

Twitter PWA

Let me start by walking through one of the better PWA experiences offered by Twitter. Over the last couple of months Twitter has changed the layout of their website significantly but what’s interesting is that it appears they’ve been moving towards a single look and feel across both their web and app experience. For example, the experience you see today on the website is basically the same as what you get if you download the Windows Store app. As you’ll see once we install their PWA that the web interface makes sense because it’s designed to work as an app.

Back in 2017, Twitter announced Twitter Lite which they talked about as being a PWA. They talked a lot about how they built it and their post is definitely worth a read. However, I want to focus on the experience they’ve built for users.

Twitter on Mobile Chrome

Let’s look first at their mobile experience. When you go to in Chrome on a mobile device, assuming you’ve signed in, you’ll see a prompt at the bottom of the screen to “Add Twitter to Home screen”. Alternatively if you’re not signed in, or you’ve dismissed the prompt, you can select Add to Home Screen from the side menu in Chrome.

Tapping on Add Twitter to Home screen displays a confirmation prompt

Tapping Add will “install” the mobile website as an application. This includes an icon that you can move around your home screen. Note that the icon is almost indistinguishable from the actual Twitter application that you can download from the store.

When you launch the newly installed Twitter website, what you see is virtually the same as the Twitter application you’d download from the store. There’s no browser chrome and it looks and behaves just like an app.

And in fact if you press and hold on the Twitter icon on the home screen and go to App info, it even displays information in the same way as it would a regular application, including the ability to Uninstall and Force stop.

Twitter on Desktop Chrome

So that’s the mobile experience. Let’s just check what the desktop experience is. It’s not much different, except for there’s no prompt to install the application. However, if you look to the right of the address bar, there’s a little circle with a plus button; hovering over it indicates it will Install Twitter. Similarly if you go to the right side-menu, there’s an option to Install Twitter.

Again, the install process prompts for user confirmation.

Once installed the Twitter website launches without the browser chrome. In addition to the usual minimize, restore and close buttons on the right side of the title bar of the window, there’s a key icon and a vertical dots icon. The key icon allows you to clear all browsing data.

The vertical dots reveals a menu with the option to Uninstall Twitter.

After installing the Twitter website as an application the Twitter icon does appear in the applications list. However, if you attempt to uninstall the Twitter website by right-clicking the icon and selecting uninstall, it’ll just take you to Add/Remove programs in Settings (I suspect Windows thinks you want to uninstall Chrome). You need to launch the Twitter website application and use the Uninstall Twitter option in the menu.

Making Uno a PWA

Now that we’ve seen how a website can be installed and then behaves just like a regular application, let’s take a look at how easily we can do this for an application that uses Uno and WebAssembly.
The firs thing that we’ll need is a manifest file. In my case I’ve called it manifest.json and I’ve put it into the root of the WASM project in my Uno solution. It’s got the following content that defines things like the icon and the name of application etc.

    "background_color": "#ffffff",
    "description": "Freakin awesome Uno web app.",
    "display": "standalone",
    "icons": [
        "src": "Icon192x192.png",
        "sizes": "192x192",
        "type": "image/png"

    "name": "Uno as a PWA",
    "short_name": "Uno PWA",
    "start_url": "/index.html",
    "theme_color": "#ffffff",
    "scope": "/"

Of course, we’ll need to add the icon – I’ve added an 192×192 png with the name Icon192x192.png to the wwwroot folder within the WASM project. I also need to connect the manifest file so that the browser knows to look for it. To do this I need to add it as a link to the web page that hosts the Uno WASM application. In the default WASM project generated by the Uno solution template, there’s no html file, since it’s automatically generated. From the Uno documentation it’s possible to add in a template html file (see the Index.html content override section in the Bootstrap readme). However, it’s also possible to just specify the name of the manifest file using the WasmPWAManifestFile attribute in the project file (see Support for PWA Manifest File section in docs).


When we now run the WASM project and bring up the developer tools on the Application tab you can select Manifest and see the information contained in the manifest.json.

Also, the plus button is on the right of the address bar (and the option to Install in the side menu), indicating that this website can be installed.

And that’s it – all you need to do to get your Uno website setup to be installed as as PWA.

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