How to install and test an MSIX package before you submit it

Three ways to install it

Sign it with a test certificate

The certificate's subject has to match the Publisher in your manifest exactly. If you use the Publisher value from Partner Center for both, the same package works for testing and for upload, because the Store replaces your signature with Microsoft's.

1. 1

   Make and trust a certificate

   With Microsoft's winapp CLI, two commands make a certificate from your manifest's Publisher and install it. The second needs PowerShell running as administrator.

   winapp cert generate --manifest .\Package.appxmanifest
   winapp cert install .\devcert.pfx

   winapp uses a password that's publicly known by default, so keep this certificate for testing only. Without winapp, our code signing guide has the PowerShell commands with New-SelfSignedCertificate and the Trusted People store.

2. 2

   Sign the package

   winapp pack signs as it builds if you pass --cert. For a package you already have, winapp sign or SignTool from the Windows SDK does it.

   winapp pack .\dist --cert .\devcert.pfx
   winapp sign .\MyApp.msix .\devcert.pfx

3. 3

   Install it

   Double-click the .msix and App Installer, which ships with Windows, opens it. Or use PowerShell:

   Add-AppxPackage -Path .\MyApp.msix

Install it unsigned on Windows 11

Microsoft says that as of Windows 11 you can install a package without signing it, to test it quickly. The manifest's Publisher needs a special OID at the end, or Windows won't register it:

<Identity Name="MyApp"
  Publisher="CN=My Name, OID.2.25.311729368913984317654407730594956997722=1"
  Version="1.0.0.0" />

Then install it with -AllowUnsigned. A package with an .exe in it installs for all users, so Microsoft says you'll usually need PowerShell running as administrator.

Add-AppxPackage -Path .\MyApp.msix -AllowUnsigned

Put the Partner Center Publisher back before you build the package you upload. Microsoft says to remove the OID before you distribute the app, and the Store rejects a Publisher that doesn't match your Product identity.

Register the unpacked folder

If you have a folder with your app and its AppxManifest.xml, you can try it before you make an .msix. Run this from the folder:

Add-AppxPackage -Register .\AppxManifest.xml

Microsoft calls this registering in development mode. If Windows answers with 0x80073CFF, it wants a developer license or sideloading. Turn on Developer Mode under Settings›System›Advanced›For developers, or on the For developers page before Windows 11 25H2. To try a change, replace the files, raise the version in the manifest and run the command again.

What to check once it's installed

• It opens from Start, by the name you reserved, and the icon has no colored plate behind it.
• It starts promptly, stays responsive and closes cleanly. Microsoft's policy 10.4.2 asks for all three.
• Every screen and feature works, including sign-in, saving files and anything that needs the internet.
• It works on a PC that never had your development tools on it. A missing runtime or file shows up here first.
• It uninstalls without leaving a broken Start entry.

Then run the Windows App Certification Kit, which Microsoft uses for the technical part of certification. Our submission checklist has the command. If icons look wrong, see MSIX icon sizes.

Common install errors

For more detail, run Get-AppxLog in PowerShell right after the failure, or open Event Viewer and look under Applications and Services Logs›Microsoft›Windows›AppXDeployment-Server.

Uninstall the test package

Uninstall it from Start, or in PowerShell with part of your package name:

Get-AppxPackage *MyApp* | Remove-AppxPackage

What StoreFast checks

Once your app is in the Store, StoreFast publishes each update from one .msix. When you drop the package, it checks that the name matches your app and that the version is higher than the live one and ends in .0, before anything is uploaded. It doesn't run your app, so install and test each build yourself first.

Questions

How do I install an .msix file?

Double-click it and App Installer, which ships with Windows, opens it. Or run Add-AppxPackage -Path .\MyApp.msix in PowerShell. Either way, the package has to be signed with a certificate your PC trusts, unless you use the unsigned option on Windows 11.

Why won't my own MSIX install?

Usually because it isn't signed, or it's signed with a test certificate your PC doesn't trust yet. Windows reports 0x800B0100 for no signature and 0x800B0109 for an untrusted certificate. Import the test certificate into Trusted People on that PC, or sign the package again.

Do I have to sign the package I upload to the Store?

No. Microsoft signs MSIX packages with its own certificate when it publishes them. You only sign to test the package on your own PCs.

Can I upload the unsigned test package to the Store?

Not as is. An unsigned test package needs a special OID value in its Publisher. Microsoft says to remove it before you distribute the app, and for the Store the Publisher has to be the exact value from Partner Center's Product identity page.

How do I uninstall a test package?

Uninstall it from Start like any app, or run Get-AppxPackage *MyApp* | Remove-AppxPackage in PowerShell, with part of your package name in place of MyApp.