Convert APPX to XAP

A legacy Windows Phone 7 or 8 device, emulator, or deployment tool may require an XAP package, while the available application is an APPX. These packages target different application models, so a filename change or archive conversion cannot make the APPX runnable as XAP.

What the APPX format is

APPX is a Windows application package format used by Windows 8, Windows 10, Windows 11, Windows Phone 8.1, and applications based on the Universal Windows Platform. Developers create it with Visual Studio and Windows SDK tools; users encounter it when installing, distributing, or archiving Windows applications.

An APPX normally contains an AppxManifest.xml file, compiled .NET or native binaries, resources, dependency declarations, an optional block map, and a digital signature. Its executable code targets a Windows Runtime, UWP, or another supported Windows application model. An APPX built for Windows Phone 8.1 may use the Windows Phone Runtime model, but that does not make it a Silverlight XAP.

What the XAP format is

XAP is a ZIP-based deployment package for Microsoft Silverlight applications, including Windows Phone 7 and Windows Phone 8 applications and some Silverlight 8.1 phone projects. A phone XAP can contain assemblies, resources, an AppManifest.xaml file, and phone-specific manifest data such as WMAppManifest.xml.

Legacy Windows Phone SDK projects generate XAP files during compilation. XAP packages are tied to the Silverlight phone runtime, the target Windows Phone version, supported processor architecture, and the corresponding signing and deployment rules. Windows Phone is discontinued, and XAP is not a general installation format on current Windows or mobile platforms.

How to produce an XAP

There is no reliable direct APPX-to-XAP converter. A functional XAP requires a Silverlight phone application built against the correct legacy SDK, not merely the files extracted from an APPX.

1. Identify the required target. Determine whether the device needs Windows Phone 7, Windows Phone 8, or a Silverlight 8.1 package. These targets require different SDKs and may not accept one another's packages.
2. Recover the original source if possible. If the developer has a Silverlight phone project, open it with the matching legacy Visual Studio and Windows Phone SDK. Visual Studio 2010 was used for many Windows Phone 7 projects, Visual Studio 2012 for Windows Phone 8, and Visual Studio 2013 for Windows Phone 8.1 Silverlight projects.
3. Inspect the APPX only when source is unavailable. Microsoft’s Windows SDK includes makeappx.exe. For example, run makeappx unpack /p Application.appx /d UnpackedApp, or open the package with 7-Zip. This exposes manifests, resources, and binaries; it does not reconstruct the original project.
4. Port the application manually. Create or restore a Windows Phone Silverlight project, then replace UWP or Windows Runtime APIs, application lifecycle code, permissions, controls, service integrations, and incompatible libraries with Silverlight phone equivalents. Re-add the recoverable images and other assets.
5. Build the target project. Set the required phone version and architecture, then choose Build → Build Solution. The legacy SDK normally writes the XAP to a project output directory such as bin/Debug or bin/Release.
6. Apply the required signing and deployment settings. A package for one phone version may fail on another, and sideloading or store deployment can require certificates and developer-unlock settings specific to that platform.

No reputable online converter can translate the APPX executable model, APIs, manifest schema, dependencies, and signing requirements into a Silverlight XAP. Online archive tools can extract or recompress files, but they cannot perform this application port; uploading a proprietary or signed package also exposes its contents to a third party.

Compatibility limitations

Renaming Application.appx to Application.xap, changing the ZIP extension, or adding AppManifest.xaml does not change the contained executable format. A Windows Runtime, UWP, or native binary from an APPX may be incompatible with the Silverlight loader, even when both packages contain .NET assemblies.

If the APPX is the only available file, you may recover images, text, metadata, and occasionally inspect managed assemblies with suitable development tools, but you normally cannot recover the source code, project configuration, original dependencies, or equivalent XAP behavior. The reverse operation is also a port rather than an archive conversion: an XAP must be rebuilt for a supported Windows application model before it can become an APPX.