Unexpected error on Microsoft.Extensions.ApiDescription.Server during build

[figgefilur1]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Hello,

I've recently updated the Microsoft.Extensions.ApiDescription.Server-package to version 9.0.12 (latest for .NET 9, as far as I'm aware), and builds now fail with Exit Code 1.

Before the update, I used version 9.0.6, which worked (even if I now revert to that version);
I've also tried 9.0.11 (previously unused) which also works, thus getting freshly downloaded when testing this.

Checking the filesystem shows that there appears to be missing files in the <..>\.nuget\<..>\9.0.12\tools\-folder (see images below).

This project cannot currently target .NET 10, thus I have not tested any versions of that yet.

P.S.: Not sure if this is the correct place to report this, or if I've been unable to find another reference to this issue.

I were unable to find another issue referencing this problem.

Thanks in advance,
Fredrik

Expected Behavior

No response

Steps To Reproduce

No response

Exceptions (if any)

The command "dotnet "C:\<REDACTED>\.nuget\packages\microsoft.extensions.apidescription.server\9.0.12\build\../tools/dotnet-getdocument.dll" --assembly "<REDACTED>.dll" --file-list "<REDACTED>.cache" --framework ".NETCoreApp,Version=v9.0" --output "<REDACTED>\docs\openapi" --project "<REDACTED>" --assets-file "<REDACTED>\obj\project.assets.json" --platform "AnyCPU" " exited with code 1.

.NET Version

No response

Anything else?

ASP.NET Core: .NET 9.0.
SDK: 9.0.307.
IDE: Visual Studio 2026, 18.2.0, January 2026 Feature Update.

Microsoft.Extensions.ApiDescription.Server-NuGet:

• 9.0.6: Working.
• 9.0.11: Working:
  
• 9.0.12: Non-Working: (Missing files?)
  

[martincostello]

For easier browsing with NuGet Package Explorer:

• Microsoft.Extensions.ApiDescription.Server@9.0.11 (✅)
• Microsoft.Extensions.ApiDescription.Server@9.0.12 (❌)

[martincostello]

Looks like this was caused by #64351 /cc @wtgodbe

[wtgodbe]

What TargetFramework is your app targeting @figgefilur1?

[figgefilur1]

@wtgodbe The TargetFramework is set as "net9.0" (<TargetFramework>net9.0</TargetFramework>), unless you mean some other TF-source that I'm not aware of

[tbright92]

I'm also experiencing the same problem and posted about it in this issue of the core repo (although I probably should've posted it here).

Our TargetFramework is also "net9.0". Can confirm that manually copying the DLL and JSON files from @figgefilur1's screenshot into the 9.0.12/tools directory allows the build to succeed.

Also confirmed that the DLL/JSON files are present in 10.0.2, so this only seems to be impacting 9.0.12. I don't have a .NET 8 project to test on though.

[tbright92]

Could this be part of the problem? Both the JSON files for 9.0.11 list netcoreapp2.1 as the RuntimeTarget.

It's .NETCoreApp v10.0 in the latest .NET 10 version.

[alexaka1]

+1, our TFM is also net9.0, after upgrading to 9.0.12 this is breaking.