What is the XAP file format?
XAP files store application packages for Microsoft Silverlight - a browser plugin framework - and later for Windows Phone 7/8.0 apps. Silverlight itself reached end of life on October 12, 2021, so XAP is now a legacy format.
Silverlight was capable of running code written in managed .NET languages such as C# and VB.NET (and dynamic languages like IronPython). The framework also offered:
- a graphics rendering engine,
- HD H.264 video streaming support (introduced in Silverlight 3.0),
- MP3 and WMA audio support,
- support for external devices (mouse and keyboard),
- DRM features.
Most web browsers offered dedicated plugins for Silverlight, including Google Chrome, Internet Explorer, Firefox, Safari, and SeaMonkey. Modern Chrome and Firefox browsers dropped support years before Silverlight's formal end of life, and Microsoft's own Edge browser never supported it.
XAP files were also used for distributing apps for Windows Phone 7 and 8.0. They store apps compressed into ZIP archives along with AppManifest.xaml or WMAppManifest.xml documents and DLL libraries used by the .NET managed runtime. Because a XAP is a standard ZIP archive, you can inspect its contents by renaming the file to .zip. Windows Phone 8.1 and later moved to the APPX packaging format, and XAP files can no longer be run on any current platform.
Security & safety
RISK: MEDIUMA XAP is inert on modern systems (no runtime to execute it), so the main risk is simply running unknown legacy code if you somehow revive it. The .dll assemblies inside can contain anything, so only inspect XAPs from sources you trust, and treat sideloaded Windows Phone packages from random sites with caution. Inspecting (rename-to-zip) is safe; executing is what carries risk.
Format details
in a nutshellPrograms that open XAP files
Windows4 apps
Visual Studio
Freemium Only useful with the original Silverlight/Windows Phone project source; legacy Silverlight tooling is unsupported in current VS versions. 
7-Zip
Open-source Right-click the .xap > 7-Zip > Open archive (a XAP is a ZIP) to view the manifest, .dll files, and resources without running anything. 
ILSpy
Open-source Extract the .dll assemblies from the XAP, then open them in ILSpy to inspect/decompile the .NET code. Technical details
deep spec| Container format | Standard ZIP archive; magic bytes PK (50 4B 03 04) at offset 0 |
| Compression | DEFLATE per ZIP entry; the outer ZIP archive itself is not additionally compressed |
| MIME type | application/x-silverlight-app |
| Silverlight manifest | AppManifest.xaml inside the archive - declares Silverlight runtime version and the managed entry-point assembly |
| Windows Phone manifest | WMAppManifest.xml inside the archive - declares target OS (7.x or 8.0), app capabilities, and app metadata |
| Code assemblies | One or more managed .NET assemblies (.dll files) compiled for the Silverlight or Windows Phone runtime CLR |
| Integrity | ZIP per-entry CRC-32; Windows Phone Store packages additionally carried a catalog digital signature |
| Encoding | Binary (ZIP container with DEFLATE-compressed managed code and resource entries) |
| Typical file size | 100 KB - 100 MB depending on app assets (UI, images, media, code) |
| Maximum archive entries | ZIP format supports up to 65,535 entries; ZIP64 extension removes this limit |
| Identification | Not distinguishable from a plain ZIP by magic bytes alone; identified by the presence of AppManifest.xaml (Silverlight) or WMAppManifest.xml (Windows Phone) inside |
| Platform support | Silverlight in browsers on Windows and macOS; Windows Phone 7 and 8.0 devices - no current platform can execute XAP files |
| Superseded by | APPX for Windows Phone 8.1 and the Universal Windows Platform; later MSIX for modern Windows apps |
| Status | Discontinued - Silverlight end of life reached; Windows Phone discontinued; no current browser or OS can run XAP packages |
| Released | 2007 (Silverlight 1.1/2); used for Windows Phone 7/8 apps (2010-2014) |
| Latest version | Windows Phone 8.0 XAP; Windows Phone 8.1+ moved app packaging toward APPX |
| Specification | www.loc.gov |
XAP conversions
Community Q&A
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