unliftedq Create or Open a Project
New app — scaffold with a template:
dotnet new winui-mvvm -n <AppName>
cd <AppName>
Creates an MVVM project with CommunityToolkit.Mvvm, TitleBar, MicaBackdrop, and Frame navigation. Do NOT mkdir first — -n creates the folder.
Existing app — read the .csproj to understand:
<TargetFramework>(e.g.,net10.0-windows10.0.26100.0)<PackageReference>versions (WindowsAppSDK, CommunityToolkit)- Project structure and established patterns
Install Packages
dotnet add package <Name>
Never specify --version — omitting it gets the latest stable and avoids outdated API mismatches.
Build & Run
Use the BuildAndRun.ps1 script (included with this skill) — it handles everything:
.\BuildAndRun.ps1
Invoke the script with mode: "async". The script stays attached to the running app so a mode: "sync" call blocks your turn for the entire lifetime of the app. The output contains the PID of the running app once the app starts, which looks like this:
✅ <pkg> launched (PID: 12345)
What the script does automatically:
- Checks Developer Mode is enabled (fails fast if not)
- Finds the
.csprojin the current directory - Auto-detects platform (x64 or ARM64)
- Builds with MSBuild (or falls back to
dotnet build) - Finds the build output folder
- Launches with
winapp run --debug-output
Options:
.\BuildAndRun.ps1 # auto-find csproj, build, run (should use async invocation)
.\BuildAndRun.ps1 MyApp.csproj # explicit project
.\BuildAndRun.ps1 -Detach # run in detached mode, no debug output or exceptions (safe to use mode: "sync")
.\BuildAndRun.ps1 -SkipRun # build only (safe to use mode: "sync")
.\BuildAndRun.ps1 /p:Configuration=Release # override defaults
If build fails: Read ALL errors, batch-fix them in one pass, then run BuildAndRun.ps1 again.
If the app crashes on launch: read_powershell the shell — first-chance exceptions appear in the output.
Common Errors
| Error | Fix |
|---|---|
| Developer Mode not enabled | Settings → System → For developers → On |
| CS0234/CS0246 missing type | Add using or dotnet add package |
| NETSDK1136 platform required | BuildAndRun.ps1 handles this automatically |
| XLS0414 XAML type not found | Add xmlns declaration |
| XDG0062 binding path missing | Check x:Bind property exists on ViewModel |
| Blank window after launch | x:Bind defaults to OneTime — add Mode=OneWay |
| App silently exits | Use winapp run, never run the .exe directly |
| XAML compiler crashes silently | Remove any PresentationCore.dll / System.Windows references |
| 0x80073CF6 package install failed | Run winapp init, check manifest publisher matches cert |
| 0x8007000B bad image format | Wrong platform target — use x64 or ARM64, not AnyCPU |
Prerequisites
| Requirement | Minimum | Recommended (fresh installs) | Install command |
|---|---|---|---|
| Windows 10 v1903+ | — | — | — |
| Developer Mode | enabled | enabled | Settings → Advanced → Developer Mode → On |
| .NET SDK | 8.0 | 10.0 | winget install Microsoft.DotNet.SDK.10 |
| winapp CLI | 0.3 | latest | winget install Microsoft.WinAppCLI |
| WinUI templates | any | latest | dotnet new install Microsoft.WindowsAppSDK.WinUI.CSharp.Templates |
If any of these are missing when you try to access them — winapp or dotnet not recognized, the WinUI templates aren't installed, Developer Mode is off — do not try to install them yourself and do not try to work around it. Stop and tell the user the prerequisite is missing and ask them to run /winui-setup (a user-invoked skill that installs and verifies everything). Once they've finished, retry the failed command.
Critical Rules
- ❌ NEVER run the packaged .exe directly — always use
winapp runorBuildAndRun.ps1 - ❌ NEVER add
<WindowsPackageType>Noneto work around launch issues - ❌ NEVER delete
Package.appxmanifest - ❌ NEVER use
AnyCPU— always x64 or ARM64
References
BuildAndRun.ps1— included with this skill, handles build + run automatically