.NET Project Structure and Build Configuration

When to Use This Skill

Use this skill when:

• Setting up a new .NET solution with modern best practices
• Configuring centralized build properties across multiple projects
• Implementing central package version management
• Setting up SourceLink for debugging and NuGet packages
• Automating version management with release notes
• Pinning SDK versions for consistent builds

---

Recommended Solution Layout

MyApp/
├── .config/
│   └── dotnet-tools.json           # Local .NET tools
├── .editorconfig
├── .gitignore
├── global.json
├── nuget.config
├── Directory.Build.props
├── Directory.Build.targets
├── Directory.Packages.props
├── MyApp.slnx                       # .NET 9+ SDK / VS 17.13+
├── src/
│   ├── MyApp.Core/
│   │   └── MyApp.Core.csproj
│   ├── MyApp.Api/
│   │   ├── MyApp.Api.csproj
│   │   ├── Program.cs
│   │   └── appsettings.json
│   └── MyApp.Infrastructure/
│       └── MyApp.Infrastructure.csproj
└── tests/
    ├── MyApp.UnitTests/
    │   └── MyApp.UnitTests.csproj
    └── MyApp.IntegrationTests/
        └── MyApp.IntegrationTests.csproj

Key principles:

• Separate src/ and tests/ directories
• One project per concern (Core/Domain, Infrastructure, API/Host)
• Solution file at the repo root
• All shared build configuration at the repo root

---

Solution File Formats

.slnx (Modern — .NET 9+)

The XML-based solution format is human-readable and diff-friendly. Requires .NET 9+ SDK or Visual Studio 17.13+.

<Solution>
  <Folder Name="/build/">
    <File Path="Directory.Build.props" />
    <File Path="Directory.Packages.props" />
    <File Path="global.json" />
    <File Path="NuGet.Config" />
  </Folder>
  <Folder Name="/src/">
    <Project Path="src/MyApp.Core/MyApp.Core.csproj" />
    <Project Path="src/MyApp.Api/MyApp.Api.csproj" />
    <Project Path="src/MyApp.Infrastructure/MyApp.Infrastructure.csproj" />
  </Folder>
  <Folder Name="/tests/">
    <Project Path="tests/MyApp.UnitTests/MyApp.UnitTests.csproj" />
    <Project Path="tests/MyApp.IntegrationTests/MyApp.IntegrationTests.csproj" />
  </Folder>
</Solution>

Migrating from .sln to .slnx

dotnet sln MySolution.sln migrate

Important: Do not keep both .sln and .slnx files in the same repository.

Creating a New .slnx Solution

# .NET 10+: Creates .slnx by default
dotnet new sln --name MySolution

# .NET 9: Specify the format explicitly
dotnet new sln --name MySolution --format slnx

dotnet sln add src/MyApp/MyApp.csproj

Benefits

• Dramatically fewer merge conflicts
• Human-readable and editable
• Consistent with modern .csproj format
• Better diff/review experience in pull requests

---

Directory.Build.props

Shared MSBuild properties applied to all projects in the directory subtree.

<Project>
  <!-- Metadata -->
  <PropertyGroup>
    <Authors>Your Team</Authors>
    <Company>Your Company</Company>
    <Copyright>Copyright © 2020-$([System.DateTime]::Now.Year) Your Company</Copyright>
    <Product>Your Product</Product>
    <PackageProjectUrl>https://github.com/yourorg/yourrepo</PackageProjectUrl>
    <RepositoryUrl>https://github.com/yourorg/yourrepo</RepositoryUrl>
    <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
  </PropertyGroup>

  <!-- C# Language Settings -->
  <PropertyGroup>
    <LangVersion>latest</LangVersion>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
    <AnalysisLevel>latest-all</AnalysisLevel>
    <NoWarn>$(NoWarn);CS1591</NoWarn>
  </PropertyGroup>

  <!-- Target Framework Definitions -->
  <PropertyGroup>
    <NetStandardLibVersion>netstandard2.0</NetStandardLibVersion>
    <NetLibVersion>net8.0</NetLibVersion>
    <NetTestVersion>net9.0</NetTestVersion>
  </PropertyGroup>

  <!-- SourceLink Configuration -->
  <PropertyGroup>
    <PublishRepositoryUrl>true</PublishRepositoryUrl>
    <EmbedUntrackSources>true</EmbedUntrackSources>
    <IncludeSymbols>true</IncludeSymbols>
    <SymbolPackageFormat>snupkg</SymbolPackageFormat>
    <DebugType>embedded</DebugType>
    <ContinuousIntegrationBuild Condition="'$(CI)' == 'true'">true</ContinuousIntegrationBuild>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.SourceLink.GitHub" PrivateAssets="All" />
  </ItemGroup>

  <!-- NuGet Package Assets -->
  <ItemGroup>
    <None Include="$(MSBuildThisFileDirectory)logo.png" Pack="true" PackagePath="\" />
    <None Include="$(MSBuildThisFileDirectory)README.md" Pack="true" PackagePath="\" />
  </ItemGroup>

  <PropertyGroup>
    <PackageIcon>logo.png</PackageIcon>
    <PackageReadmeFile>README.md</PackageReadmeFile>
  </PropertyGroup>

  <!-- Global Using Statements -->
  <ItemGroup>
    <Using Include="System.Collections.Immutable" />
  </ItemGroup>
</Project>

Nested Directory.Build.props

Inner files do not automatically import outer files:

<!-- src/Directory.Build.props -->
<Project>
  <Import Project="$([MSBuild]::GetPathOfFileAbove('Directory.Build.props', '$(MSBuildThisFileDirectory)../'))" />
  <PropertyGroup>
    <!-- src-specific settings -->
  </PropertyGroup>
</Project>

---

Directory.Build.targets

Imported after project evaluation. Use for:

• Shared analyzer package references
• Custom build targets
• Conditional logic based on project type

<Project>
  <ItemGroup>
    <PackageReference Include="Meziantou.Analyzer" PrivateAssets="all" />
    <PackageReference Include="Microsoft.CodeAnalysis.BannedApiAnalyzers" PrivateAssets="all" />
  </ItemGroup>
</Project>

---

Directory.Packages.props - Central Package Management

CPM centralizes all NuGet package versions at the repo root. Individual .csproj files reference packages without a Version attribute.

<Project>
  <PropertyGroup>
    <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
    <CentralPackageTransitivePinningEnabled>true</CentralPackageTransitivePinningEnabled>
  </PropertyGroup>

  <PropertyGroup>
    <AkkaVersion>1.5.35</AkkaVersion>
    <AspireVersion>9.1.0</AspireVersion>
  </PropertyGroup>

  <ItemGroup Label="App Dependencies">
    <PackageVersion Include="Akka" Version="$(AkkaVersion)" />
    <PackageVersion Include="Akka.Cluster" Version="$(AkkaVersion)" />
    <PackageVersion Include="Microsoft.Extensions.Hosting" Version="9.0.0" />
  </ItemGroup>

  <ItemGroup Label="Test Dependencies">
    <PackageVersion Include="xunit.v3" Version="3.2.2" />
    <PackageVersion Include="xunit.runner.visualstudio" Version="3.1.5" />
    <PackageVersion Include="FluentAssertions" Version="7.0.0" />
    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
    <PackageVersion Include="coverlet.collector" Version="8.0.0" />
  </ItemGroup>

  <ItemGroup Label="Build Dependencies">
    <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="8.0.0" />
  </ItemGroup>
</Project>

Consuming Packages (No Version Needed)

<!-- In MyApp.csproj -->
<ItemGroup>
  <PackageReference Include="Akka" />
  <PackageReference Include="Microsoft.Extensions.Hosting" />
</ItemGroup>

Version Overrides

<PackageReference Include="Newtonsoft.Json" VersionOverride="13.0.3" />

---

.editorconfig

Place at the repo root to enforce consistent code style:

root = true

[*]
indent_style = space
indent_size = 4
end_of_line = lf
charset = utf-8
trim_trailing_whitespace = true
insert_final_newline = true

[*.{csproj,props,targets,xml,json,yml,yaml}]
indent_size = 2

[*.cs]
csharp_style_namespace_declarations = file_scoped:warning
csharp_prefer_braces = true:warning
csharp_style_var_for_built_in_types = true:suggestion
csharp_style_var_when_type_is_apparent = true:suggestion
dotnet_style_require_accessibility_modifiers = always:warning
csharp_style_prefer_pattern_matching = true:suggestion
csharp_style_prefer_switch_expression = true:suggestion
csharp_using_directive_placement = outside_namespace:warning
dotnet_sort_system_directives_first = true

dotnet_naming_rule.private_fields_should_be_camel_case.symbols = private_fields
dotnet_naming_rule.private_fields_should_be_camel_case.style = camel_case_underscore
dotnet_naming_rule.private_fields_should_be_camel_case.severity = warning
dotnet_naming_symbols.private_fields.applicable_kinds = field
dotnet_naming_symbols.private_fields.applicable_accessibilities = private
dotnet_naming_style.camel_case_underscore.required_prefix = _
dotnet_naming_style.camel_case_underscore.capitalization = camel_case

---

global.json - SDK Version Pinning

{
  "sdk": {
    "version": "9.0.200",
    "rollForward": "latestFeature"
  }
}

Roll Forward Policies

Policy	Behavior
disable	Exact version required
patch	Same major.minor, latest patch
feature	Same major, latest minor.patch
latestFeature	Same major, latest feature band
minor	Same major, latest minor
latestMinor	Same major, latest minor
major	Latest SDK (not recommended)

Recommended: latestFeature - Allows patch updates within the same feature band.

---

nuget.config

Configure package sources and security:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <solution>
    <add key="disableSourceControlIntegration" value="true" />
  </solution>

  <packageSources>
    <clear />
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
  </packageSources>

  <packageSourceMapping>
    <packageSource key="nuget.org">
      <package pattern="*" />
    </packageSource>
  </packageSourceMapping>
</configuration>

The <clear /> + explicit sources + <packageSourceMapping> pattern prevents supply-chain attacks.

For private feeds:

<packageSources>
  <clear />
  <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
  <add key="internal" value="https://pkgs.dev.azure.com/myorg/_packaging/myfeed/nuget/v3/index.json" />
</packageSources>
<packageSourceMapping>
  <packageSource key="nuget.org">
    <package pattern="*" />
  </packageSource>
  <packageSource key="internal">
    <package pattern="MyCompany.*" />
  </packageSource>
</packageSourceMapping>

---

NuGet Audit

.NET 9+ enables NuGetAudit by default:

<PropertyGroup>
  <NuGetAudit>true</NuGetAudit>
  <NuGetAuditLevel>low</NuGetAuditLevel>
  <NuGetAuditMode>all</NuGetAuditMode>
</PropertyGroup>

---

Lock Files

Enable deterministic restores:

<PropertyGroup>
  <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile>
</PropertyGroup>

In CI:

dotnet restore --locked-mode

---

SourceLink and Deterministic Builds

For libraries published to NuGet:

<PropertyGroup>
  <PublishRepositoryUrl>true</PublishRepositoryUrl>
  <EmbedUntrackSources>true</EmbedUntrackSources>
  <DebugType>embedded</DebugType>
  <ContinuousIntegrationBuild Condition="'$(CI)' == 'true'">true</ContinuousIntegrationBuild>
</PropertyGroup>
<ItemGroup>
  <PackageReference Include="Microsoft.SourceLink.GitHub" PrivateAssets="all" />
</ItemGroup>

---

Version Management with RELEASE_NOTES.md

#### 1.2.0 January 15th 2025 ####

- Added new feature X
- Fixed bug in Y

#### 1.1.0 December 10th 2024 ####

- Initial release

CI/CD Integration

- name: Update version from release notes
  shell: pwsh
  run: ./build.ps1

- name: Build
  run: dotnet build -c Release

- name: Pack with tag version
  run: dotnet pack -c Release /p:PackageVersion=${{ github.ref_name }}

---

Quick Reference

File	Purpose
MySolution.slnx	Modern XML solution file
Directory.Build.props	Centralized build properties
Directory.Packages.props	Central package version management
global.json	SDK version pinning
NuGet.Config	Package source configuration
RELEASE_NOTES.md	Version history
.editorconfig	Code style enforcement
.config/dotnet-tools.json	Local .NET tools

---

References

• .NET Library Design Guidance
• Central Package Management
• .slnx Format
• Directory.Build.props
• SourceLink
• NuGet Audit