What is the APPX file format?
The .appx format was introduced alongside Windows 8 and Windows Phone 8.1 as a file distribution format for applications available on the Microsoft Store. An application package is a container-type file that follows the Open Packaging Convention (OPC) standard, describing a hierarchical structure for storing data and other resources in a ZIP archive format. Internally, every .appx archive includes three required files: AppxManifest.xml (app identity, capabilities, and entry points), AppxBlockMap.xml (a SHA-256 hash map for block-level integrity verification), and AppxSignature.p7x (the package's cryptographic signature).
Submitting .appx files to the Microsoft Store
An .appx file is an archive that contains the application in its final form, ready for distribution and installation. Submitting an .appx package to the Microsoft Store requires the developer to pick a name for the app, attach details regarding the sale model and list of available functions. Each submitted package must undergo a security and compatibility testing procedure. For Store submissions, the .appx is typically wrapped in an .appxupload file, which can also bundle optional .pdb debugging symbols.
Advantages of .appx packages
Streamlined distribution of packages between computers, tablets, and phones - devices that vary in their characteristics - was the main goal that led to the creation of the .appx format. Traditional applications relied on clunky installers notorious for causing problems on mobile systems. .appx addressed this by running apps inside a UWP sandbox (AppContainer), with permissions declared upfront in the manifest rather than granted at install time. Multiple architecture-specific packages can be grouped into an .appxbundle for a single Store submission.
Additional information
The .appx format has been largely superseded by .msix since 2018, which extends the same OPC/ZIP container with improved reliability and enterprise deployment features. Packages can be installed on Windows via PowerShell using Add-AppxPackage, or through the built-in App Installer. Sideloading .appx files outside the Store requires Developer Mode or the "Sideload apps" setting to be enabled. The maximum size of an .appx file is 2 GB.
Security & safety
RISK: MEDIUMAPPX is a real installer that runs code, so it carries the usual 'installing software' risk - but it is safer by design than a raw EXE: packages must be digitally SIGNED, and Windows will refuse to install an unsigned or untrusted one, install into a sandbox, and uninstall cleanly. The practical danger is users disabling protections to sideload - being told to enable developer mode and install a stranger's certificate into Trusted Root to force an untrusted package is exactly how a malicious package gets in. Only sideload APPX/MSIX from sources you trust; check who signed it. Inspect contents first by opening it as a ZIP with 7-Zip.
Format details
in a nutshellPrograms that open APPX files
Windows4 apps
Microsoft Visual Studio
Freemium Developer tool: create, sign and deploy APPX/MSIX packages (Windows Application Packaging Project). Not for end-users just opening one. 
7-Zip
Open-source Right-click > Open archive to INSPECT contents (it's a ZIP) without installing - useful to read AppxManifest.xml or extract assets. 
Windows PowerShell
Built-in Run: Add-AppxPackage -Path C:\path\app.appx (use for bundles or when the GUI fails). Add-AppxProvisionedPackage installs for all users. 
App Installer (built-in)
Built-in Double-click the .appx/.msix; the built-in App Installer shows the app and an Install button (sideloading must be allowed and the package trusted). Technical details
deep spec| Container format | ZIP-based Open Packaging Convention (OPC) archive |
| Magic bytes | 50 4B 03 04 ("PK") at offset 0 - standard ZIP local file header signature |
| MIME type | application/appx |
| Manifest file | AppxManifest.xml - declares app identity, version, capabilities, entry points, and target device families |
| Block map file | AppxBlockMap.xml - SHA-256 hash map covering every 64 KB block for tamper-evident integrity verification |
| Signature file | AppxSignature.p7x - PKCS #7 digital signature; package must be signed to install on Windows |
| Maximum package size | 2 GB |
| Target platforms | Windows 8, 8.1, 10, 11; Windows Phone 8.1 (legacy UWP/WinRT apps) |
| Sandboxing model | UWP AppContainer - app runs in an isolated process with capabilities declared in AppxManifest.xml |
| Installation command | Add-AppxPackage (PowerShell) or App Installer GUI; no traditional MSI installer chain |
| Packaging tool | MakeAppx.exe (Windows SDK command-line) or Microsoft Visual Studio packaging wizard |
| Sideloading requirement | Requires Developer Mode or "Sideload apps" enabled in Windows Settings (or Group Policy in enterprise) |
| Store upload variant | .appxupload - wraps .appx with optional .pdb symbol files for Microsoft Store submission |
| Bundle variant | .appxbundle - groups multiple architecture-specific .appx packages into one Store submission |
| Successor format | .msix - superseded .appx starting with Windows 10 version 1809 (October 2018) |
| Signing requirement | All .appx packages must be digitally signed; self-signed certificates accepted for development and sideloading |
| Released | 2012 (Windows 8); largely superseded by MSIX since 2018 |
| Specification | learn.microsoft.com |
APPX conversions
Community Q&A
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