What Is a .MSIX File?

MSIX Windows App Package (.msix)

Overview

MSIX is Microsoft's current application packaging format for Windows, introduced in 2018 to replace both the Store-oriented AppX format and, over time, traditional MSI installers. An .msix file is a signed ZIP archive containing an application's files, a manifest describing it, and the metadata Windows needs to install, update and remove it cleanly.

The format's defining property is containment. An MSIX app installs into a protected per-package folder, its registry writes go into a private hive, and uninstalling removes everything without leftovers. That is what makes it the format the Microsoft Store, Windows Package Manager (winget) and enterprise deployment tools prefer.

Technical Specifications

• MIME Type: application/msix
• File Extensions: .msix (single package), .msixbundle (several architectures in one), .msixupload (Store submission), .appinstaller (an XML pointer to an MSIX for web install)
• Category: Package
• Container: ZIP, following the Open Packaging Conventions
• Signing: mandatory; a package without a valid Authenticode signature will not install
• Introduced: Windows 10 version 1809 (2018); also supported on Windows 11 and, via the MSIX Core project, Windows 7 and 8.1
• Magic bytes: 50 4B 03 04 (PK..)

Identification

A .msix is a ZIP. What marks it as MSIX are the files at the archive root:

unzip -l app.msix
  AppxManifest.xml         the package identity, capabilities, entry points
  AppxBlockMap.xml         hashes of every 64 KB block, for differential updates
  AppxSignature.p7x        the Authenticode signature over the block map
  [Content_Types].xml
  Assets/                  icons and tiles
  app.exe, *.dll ...       the application itself

The same layout with an older manifest schema is an AppX file; MSIX is a superset.

File Structure

Package
├── AppxManifest.xml       identity (Name, Publisher, Version), dependencies, declared capabilities,
│                          application entry points, file associations, protocol handlers
├── AppxBlockMap.xml       SHA-256 per block: Windows downloads only changed blocks on update
├── AppxSignature.p7x      signature; publisher must match the manifest Publisher exactly
├── Resources.pri          compiled string and image resources
├── VFS/                   virtual file system: redirected writes to Program Files, Windows, AppData
└── registry.dat           the app's virtualised registry hive

The block map is the clever part: because every block is hashed, Windows can update an installed app by fetching only the blocks that changed, and it can verify a package without reading all of it.

History and Development

Windows 8 introduced AppX for Store apps, with strong sandboxing that traditional desktop software could not satisfy. The Desktop Bridge (2016) let Win32 apps into AppX, and MSIX (2018) merged the two paths into one format with a published specification and an open-source SDK, so third-party installer tools could produce it.

Microsoft positioned MSIX as the successor to MSI and ClickOnce. Adoption has been real but partial: winget and the Store favour it, enterprise tools (Intune, SCCM) deploy it, and many developers still ship MSI or EXE installers because MSIX's containment breaks software that expects to write anywhere it likes.

Common Use Cases

• Microsoft Store apps, including repackaged classic desktop applications
• Enterprise deployment through Intune, Configuration Manager and MSIX app attach for Azure Virtual Desktop
• Direct web distribution via .appinstaller files, which support automatic updates
• winget packages for many open-source and commercial tools
• Windows Terminal, PowerToys, Notepad and other Microsoft apps are distributed as MSIX

How to Open an MSIX File

To install it

• Double-click on Windows 10 (1809+) or Windows 11. App Installer shows the publisher, requested capabilities and an Install button. Sideloading must be enabled (Settings, Apps, Advanced app settings, or Developer settings on older builds); it is on by default in Windows 11.
• PowerShell: Add-AppxPackage .\app.msix installs for the current user; Add-AppxProvisionedPackage provisions for all users on a machine.
• winget: winget install <id> fetches and installs MSIX packages from the community repository.

If installation fails with a certificate error, the package is signed with a certificate Windows does not trust. For an internal or test package, install the publisher's certificate into Trusted People first; for anything else, treat the error as a warning and verify where the file came from.

To look inside without installing

# Any ZIP tool
unzip -l app.msix
unzip app.msix AppxManifest.xml -d inspect/

# PowerShell
Expand-Archive app.msix -DestinationPath inspect
Get-Content inspect\AppxManifest.xml

On Windows, 7-Zip opens .msix directly. The manifest tells you the publisher, version, and what the app can do (<Capabilities>), which is worth reading before installing anything from an unfamiliar source.

Verify the signature

Get-AuthenticodeSignature .\app.msix

A Valid status with a recognisable publisher is the point of the format; NotSigned or UnknownError means the package should not be installed.

Managing installed packages

Get-AppxPackage | Select Name, Version, PackageFullName
Remove-AppxPackage <PackageFullName>

How to Create or Convert an MSIX Package

• Visual Studio: a Windows Application Packaging Project wraps a desktop app and produces signed MSIX.
• MSIX Packaging Tool (free, Microsoft Store): records an existing MSI or EXE installer and converts it to MSIX, the route most IT departments use.
• Command line: makeappx pack /d folder /p app.msix then signtool sign /fd SHA256 /a app.msix, both from the Windows SDK.
• Third-party: Advanced Installer, InstallShield and WiX (via the MSIX extension) all emit MSIX alongside MSI.
• MSIX to MSI: there is no direct conversion. Repackage from the original installer, or deploy the MSIX with tools that support it.

Advantages

• Clean install and uninstall: no leftover files or registry entries.
• Differential updates through the block map.
• Mandatory signing gives a verifiable publisher.
• Multiple distribution channels: Store, winget, web, enterprise tools.
• Published specification and open SDK.

Limitations

• Containment breaks some apps: software that writes to its own install folder, installs drivers or services, or depends on registry tricks needs rework.
• Signing friction for small developers and internal tools.
• Windows 10 1809 or later required for native support.
• Not an archive for people: the ZIP structure is a packaging detail, not a way to distribute files.

Related Formats

• MSI: the Windows Installer format MSIX is meant to succeed.
• ZIP: the underlying container.
• PEBIN: the executables and DLLs inside the package.
• APK: Android's equivalent signed-ZIP app package.
• NUPKG: another Open Packaging Conventions format from Microsoft.