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Create package extensions for Windows App SDK apps

Package extensions expand the app extension model by allowing broader content sharing between packages. A package extension host can accept extensions from any package, making it suitable for platform-level extensibility scenarios.

Note

Package extensions require Windows 11 and use the uap17 namespace. For an earlier-compatible approach, see App extensions which use uap3.

Package extensions vs. app extensions

Feature App extensions (uap3) Package extensions (uap17)
Minimum OS Windows 10 1607 Windows 11
Scope Per-application Per-package
Content sharing Public folder only Full package content access
Manifest namespace uap3:AppExtension uap17:PackageExtension

Declare a package extension host

Add a PackageExtensionHost declaration to the host app's manifest:

<Package xmlns:uap17="http://schemas.microsoft.com/appx/manifest/uap/windows10/17" ...>
  <Applications>
    <Application ...>
      <Extensions>
        <uap17:Extension Category="windows.packageExtensionHost">
          <uap17:PackageExtensionHost>
            <uap17:Name>com.example.myplatform.extensions</uap17:Name>
          </uap17:PackageExtensionHost>
        </uap17:Extension>
      </Extensions>
    </Application>
  </Applications>
</Package>

Declare a package extension

In the extension package's manifest:

<Package xmlns:uap17="http://schemas.microsoft.com/appx/manifest/uap/windows10/17" ...>
  <Applications>
    <Application ...>
      <Extensions>
        <uap17:Extension Category="windows.packageExtension">
          <uap17:PackageExtension Name="com.example.myplatform.extensions"
                                   Id="MyExtension"
                                   DisplayName="My Extension"
                                   Description="Adds features to the platform">
            <uap17:Properties>
              <ExtensionType>content</ExtensionType>
              <Version>1.0</Version>
            </uap17:Properties>
          </uap17:PackageExtension>
        </uap17:Extension>
      </Extensions>
    </Application>
  </Applications>
</Package>

Discover package extensions

Use the same AppExtensionCatalog API to discover package extensions at runtime. The host name matches the Name declared in the manifest:

var catalog = AppExtensionCatalog.Open("com.example.myplatform.extensions");
var extensions = await catalog.FindAllAsync();

foreach (var ext in extensions)
{
    System.Diagnostics.Debug.WriteLine(
        $"Found extension: {ext.DisplayName} ({ext.Id})");

    // Read custom properties
    var properties = await ext.GetExtensionPropertiesAsync();
    // Access properties as needed
}

Best practices

  • Use a reverse-domain naming convention for extension names (for example, com.company.app.extensions).
  • Version your extension protocol so host apps can handle old and new extension formats.
  • Validate extension content before using it — extensions come from other packages and should not be blindly trusted.

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