Validate Sdk

Install and Validate .NET SDK from Azure DevOps Internal Build

Follow these steps to install and validate a .NET SDK from an internal Azure DevOps build (typically from dnceng/internal).

This skill can be run from any directory, including inside a repo like dotnet/roslyn. The SDK is installed to a temp folder and validation runs in a separate temp folder, so nothing in the user's working directory is created, modified, or depended upon.

This skill requires the ADO MCP server configured for the dnceng organization to be available in your session.

How to Invoke This Skill

In a copilot session with an ADO MCP server configured for the dnceng organization, ask something like:

• "Install the .NET SDK from this build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2919304"
• "Install .NET SDK from ADO build 2919304"
• "Use /validate-sdk to set up the SDK from build 2919304"

Required Input

The user must provide one of the following:

• An Azure DevOps build URL from dev.azure.com/dnceng/internal containing a buildId query parameter
• A numeric build ID (e.g., 2919304) from the dnceng/internal project

What Does NOT Work as Input

• SharePoint/OneNote links (e.g., microsoft.sharepoint.com/...) — these are documentation pages, not build links. If the user provides one, ask them for the Azure DevOps build URL or build ID instead.
• GitHub links — this skill is for Azure DevOps builds, not GitHub Actions.
• NuGet package versions — this skill installs the full SDK, not individual packages.

If the user doesn't have the build URL or ID, suggest they look for a link like: https://dev.azure.com/dnceng/internal/_build/results?buildId=XXXXXXX in their signoff document or validation instructions.

Step 1: Get the Build ID

Extract the buildId from the Azure DevOps URL. For example, from: https://dev.azure.com/dnceng/internal/_build/results?buildId=2919304&view=artifacts The build ID is 2919304.

Step 2: Get the SDK Version from the Build

Use the ADO MCP tool ado-pipelines_get_build_status with project: "internal" and the buildId to retrieve the build report. The build number in the report contains the SDK version. Parse out the version portion (e.g., 11.0.100-preview.2.26154.117 from build number 20260305.1-11.0.100-preview.2.26154.117-304630).

The SDK version follows the pattern X.Y.Z-preview.N.NNNNN.NNN and appears between the date prefix and the trailing BAR build ID.

Step 3: Install Using dotnet-install Script

Download and run the official dotnet-install script with the exact SDK version. Install into a temp folder so there is no dependency on the user's working directory or any repo:

$sdkDir = "$env:TEMP\validate-sdk-dotnet"
$installScript = "$env:TEMP\dotnet-install.ps1"
Invoke-WebRequest -Uri "https://dot.net/v1/dotnet-install.ps1" -OutFile $installScript

# Install the specific SDK version to a temp directory
& $installScript -Version "<SDK_VERSION>" -InstallDir $sdkDir

The script will automatically try multiple feeds:

• https://builds.dotnet.microsoft.com/dotnet (primary public feed)
• https://ci.dot.net/public (CI public feed — internal preview builds are often available here)

If both feeds return 404, the SDK may not yet be published. Check with the user.

For Linux/macOS, use the bash version instead:

sdkDir="/tmp/validate-sdk-dotnet"
curl -fsSL https://dot.net/v1/dotnet-install.sh -o /tmp/dotnet-install.sh
chmod +x /tmp/dotnet-install.sh
/tmp/dotnet-install.sh --version <SDK_VERSION> --install-dir $sdkDir

Step 4: Verify Installation

Run the installed dotnet to confirm:

& "$env:TEMP\validate-sdk-dotnet\dotnet.exe" --version

This should print the exact SDK version that was requested.

Troubleshooting: If dotnet.exe is not found in the install directory, the dotnet host may not have been downloaded (the directory will only contain host/, sdk/, shared/ subdirectories without a dotnet.exe). In this case, remove the directory and reinstall:

Remove-Item -Recurse -Force "$env:TEMP\validate-sdk-dotnet" -ErrorAction SilentlyContinue
& $installScript -Version "<SDK_VERSION>" -InstallDir "$env:TEMP\validate-sdk-dotnet"

Step 5: Configure for Use

The SDK is installed to a temp directory, not system-wide. This means dotnet --list-sdks using the system dotnet will NOT show it. This is by design — it avoids affecting the user's system .NET setup.

To use the locally installed SDK:

• Run directly: $env:TEMP\validate-sdk-dotnet\dotnet.exe
• Or prepend to PATH for the current session: $env:PATH = "$env:TEMP\validate-sdk-dotnet;$env:PATH"

Step 6: Validate with #error version

Use a file-based app (a .NET 10+ feature) to extract compiler details. This must run in an isolated temp folder to avoid interference from global.json, .sln, or .csproj files in the user's working directory (e.g., a roslyn repo checkout).

1. Create a temp directory with app.cs and a pinned global.json. The #:property directive adds the internal preview feed so dotnet run can restore the runtime packs for a not-yet-public build.

   ⚠️ The feed name must match the SDK's .NET major version. The feed is named dotnet<MAJOR> where <MAJOR> is the major version of the SDK you installed. For an 11.0.x SDK use dotnet11; for a 12.0.x SDK use dotnet12; for a 10.0.x SDK use dotnet10. Do not hardcode dotnet11 — derive it from <SDK_VERSION>. Using the wrong feed will fail restore with NU1102. See the feed table at https://github.com/dotnet/dotnet/blob/main/docs/builds-table.md.

   # Derive the feed name from the SDK major version so this works for any release (dotnet11, dotnet12, ...)
   $sdkMajor = ([version](("<SDK_VERSION>" -split '-')[0])).Major
   $feed = "https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet$sdkMajor/nuget/v3/index.json"
   
   $testDir = "$env:TEMP\validate-sdk-test"
   New-Item -ItemType Directory -Path $testDir -Force | Out-Null
   Set-Content -Path "$testDir\app.cs" -Value @"
   #:property RestoreAdditionalProjectSources=$feed
   #error version
   "@
   # Pin the SDK version to prevent any parent global.json from overriding it
   Set-Content -Path "$testDir\global.json" -Value '{"sdk":{"version":"<SDK_VERSION>","allowPrerelease":true}}'
   

   Why the #:property feed matters: For preview builds, the matching runtime packs (e.g. Microsoft.NETCore.App.Runtime.*) are often not yet on nuget.org, so dotnet run fails during restore with NU1102: Unable to find package ... before it ever compiles. Adding the internal preview feed via RestoreAdditionalProjectSources lets restore succeed.

2. Run the file-based app from the temp directory using the installed SDK. You must cd into the temp directory and set DOTNET_MULTILEVEL_LOOKUP=0 to ensure full isolation from the user's environment:

   Push-Location $testDir
   $env:DOTNET_MULTILEVEL_LOOKUP = "0"
   & "$env:TEMP\validate-sdk-dotnet\dotnet.exe" run app.cs 2>&1 | Select-String -Pattern "CS8304"
   Pop-Location
   

   Why this isolation matters: Without cd + global.json + DOTNET_MULTILEVEL_LOOKUP=0, the dotnet CLI walks up the directory tree looking for global.json. If run from inside a repo like dotnet/roslyn, it would find the repo's global.json and try to use a different SDK version, causing the validation to fail or test the wrong compiler.

3. The build is expected to fail (exit code non-zero) because #error version is a deliberate compile error. The success criterion is seeing the CS8304 diagnostic in the output. Look for the CS8304 line which contains:

   • Compiler version (e.g., 5.6.0-2.26154.117)
   • Compiler commit SHA in parentheses (e.g., 6dbf4ee311820b91535cc405fb9f72f3e1ec85fc)
   • Language version (e.g., preview)

4. Clean up:

   Remove-Item -Recurse -Force "$env:TEMP\validate-sdk-test" -ErrorAction SilentlyContinue
   

Step 7: Trace the Roslyn SHA

The compiler commit SHA from Step 6 is a commit in the dotnet/dotnet VMR (Virtual Mono Repo), not dotnet/roslyn directly.

1. Look up the compiler SHA in dotnet/dotnet using github-mcp-server-get_commit (owner: dotnet, repo: dotnet).
2. Fetch src/source-manifest.json at that commit using github-mcp-server-get_file_contents (owner: dotnet, repo: dotnet, path: src/source-manifest.json, sha: <COMPILER_SHA>).
3. In the JSON, find the entry with "path": "roslyn" and extract its commitSha — this is the actual dotnet/roslyn commit.
4. Look up that Roslyn SHA using github-mcp-server-get_commit (owner: dotnet, repo: roslyn) to get the commit summary and date.

Step 8: Output Validation Report

Output a report in this format:

## .NET SDK Validation Report

- **SDK Version:** `<SDK_VERSION>`
- **Compiler Version:** `<COMPILER_VERSION>`
- **dotnet/dotnet commit:** https://github.com/dotnet/dotnet/commit/<DOTNET_DOTNET_SHA>
- **dotnet/roslyn commit:** https://github.com/dotnet/roslyn/commit/<ROSLYN_SHA>

**Last Roslyn commit:** "<COMMIT_SUMMARY>" by <AUTHOR> — merged <DATE>.

Use full SHAs (not shortened) and plain URLs (not markdown link syntax).

Notes

• Build artifacts can also be explored via ado-pipelines_get_build_log and ado-pipelines_get_build_log_by_id if you need to inspect specific asset names.
• The dotnet-install script approach is preferred over downloading artifacts directly, as the SDK zip is typically published to the CI feeds even for preview builds.