dotnet-nuget-authoring

NuGet package authoring for .NET library authors: SDK-style .csproj package properties (PackageId, PackageTags, PackageReadmeFile, PackageLicenseExpression), source generator NuGet packaging with analyzers/dotnet/cs/ folder layout and buildTransitive targets, multi-TFM packages, symbol packages (snupkg) with deterministic builds, package signing (author signing with certificates, repository signing), package validation (EnablePackageValidation, Microsoft.DotNet.ApiCompat.Task for API compatibility), and NuGet versioning strategies (SemVer 2.0, pre-release suffixes, NBGV integration).

Version assumptions: .NET 8.0+ baseline. NuGet client bundled with .NET 8+ SDK. Microsoft.DotNet.ApiCompat.Task 8.0+ for API compatibility validation.

Scope boundary: This skill owns NuGet package authoring for library consumers -- the properties, metadata, packaging layout, signing, and validation. Project-level NuGet configuration (Central Package Management, SourceLink, nuget.config, NuGet Audit, lock files) is owned by [skill:dotnet-project-structure]. CI/CD publish workflows (NuGet push to feeds, container image push) are owned by [skill:dotnet-gha-publish] and [skill:dotnet-ado-publish]. CLI tool packaging (Homebrew, apt, winget, Scoop, dotnet tool) is owned by [skill:dotnet-cli-packaging].

Out of scope: Central Package Management, SourceLink, nuget.config, NuGet Audit -- see [skill:dotnet-project-structure]. CI/CD NuGet push workflows -- see [skill:dotnet-gha-publish] and [skill:dotnet-ado-publish]. CLI tool packaging and distribution -- see [skill:dotnet-cli-packaging]. Roslyn analyzer authoring (Roslyn API, diagnostic descriptors) -- see [skill:dotnet-roslyn-analyzers]. Release lifecycle and NBGV setup -- see [skill:dotnet-release-management].

Cross-references: [skill:dotnet-project-structure] for CPM, SourceLink, nuget.config, [skill:dotnet-gha-publish] for CI NuGet push workflows, [skill:dotnet-ado-publish] for ADO NuGet push workflows, [skill:dotnet-cli-packaging] for CLI tool distribution formats, [skill:dotnet-csharp-source-generators] for Roslyn source generator authoring, [skill:dotnet-release-management] for release lifecycle and NBGV setup, [skill:dotnet-roslyn-analyzers] for Roslyn analyzer authoring.

SDK-Style Package Properties

Every NuGet package starts with MSBuild properties in the .csproj. SDK-style projects produce NuGet packages with dotnet pack -- no .nuspec file required.

Essential Package Metadata

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <PackageId>MyCompany.Widgets</PackageId>
    <Version>1.0.0</Version>
    <Authors>My Company</Authors>
    <Description>A library for managing widgets with fluent API support.</Description>
    <PackageTags>widgets;fluent;dotnet</PackageTags>
    <PackageLicenseExpression>MIT</PackageLicenseExpression>
    <PackageProjectUrl>https://github.com/mycompany/widgets</PackageProjectUrl>
    <RepositoryUrl>https://github.com/mycompany/widgets</RepositoryUrl>
    <RepositoryType>git</RepositoryType>

    <!-- README displayed on nuget.org package page -->
    <PackageReadmeFile>README.md</PackageReadmeFile>

    <!-- Package icon (128x128 PNG recommended) -->
    <PackageIcon>icon.png</PackageIcon>

    <!-- Generate XML docs for IntelliSense -->
    <GenerateDocumentationFile>true</GenerateDocumentationFile>

    <!-- Deterministic builds for reproducibility -->
    <ContinuousIntegrationBuild Condition="'$(CI)' == 'true'">true</ContinuousIntegrationBuild>
  </PropertyGroup>

  <!-- Include README and icon in the package -->
  <ItemGroup>
    <None Include="README.md" Pack="true" PackagePath="\" />
    <None Include="icon.png" Pack="true" PackagePath="\" />
  </ItemGroup>
</Project>

Property Reference

Directory.Build.props for Shared Metadata

For multi-project repos, set common properties in Directory.Build.props:

<!-- Directory.Build.props (repo root) -->
<Project>
  <PropertyGroup>
    <Authors>My Company</Authors>
    <PackageLicenseExpression>MIT</PackageLicenseExpression>
    <PackageProjectUrl>https://github.com/mycompany/widgets</PackageProjectUrl>
    <RepositoryUrl>https://github.com/mycompany/widgets</RepositoryUrl>
    <RepositoryType>git</RepositoryType>
    <Copyright>Copyright 2024 My Company</Copyright>
  </PropertyGroup>
</Project>

Individual .csproj files then only set package-specific properties (PackageId, Description, PackageTags).

Source Generator NuGet Packaging

Source generators and analyzers require a specific NuGet package layout. The generator DLL must be placed in the analyzers/dotnet/cs/ folder, not the lib/ folder. For Roslyn source generator authoring (IIncrementalGenerator, syntax/semantic analysis), see [skill:dotnet-csharp-source-generators]. This section covers NuGet packaging of generators only.

Project Setup for Source Generator Package

<!-- MyCompany.Generators.csproj -->
<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
    <EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
    <IsRoslynComponent>true</IsRoslynComponent>

    <!-- Package metadata -->
    <PackageId>MyCompany.Generators</PackageId>
    <Description>Source generators for widget auto-registration.</Description>

    <!-- Do NOT include generator DLL in lib/ folder -->
    <IncludeBuildOutput>false</IncludeBuildOutput>
    <SuppressDependenciesWhenPacking>true</SuppressDependenciesWhenPacking>

    <!-- Generator must target netstandard2.0 for Roslyn host compat -->
    <IsPackable>true</IsPackable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.8.0" PrivateAssets="all" />
  </ItemGroup>

  <!-- Place generator DLL in analyzers folder -->
  <ItemGroup>
    <None Include="$(OutputPath)$(AssemblyName).dll"
          Pack="true"
          PackagePath="analyzers/dotnet/cs"
          Visible="false" />
  </ItemGroup>
</Project>

Adding Build Props/Targets

When a source generator needs to set MSBuild properties in consuming projects, use the buildTransitive folder:

<!-- build/MyCompany.Generators.props -->
<Project>
  <PropertyGroup>
    <MyCompanyGeneratorsEnabled>true</MyCompanyGeneratorsEnabled>
  </PropertyGroup>
  <ItemGroup>
    <!-- Example: add additional files for generator to consume -->
    <CompilerVisibleProperty Include="MyCompanyGeneratorsEnabled" />
  </ItemGroup>
</Project>

Include buildTransitive content in the package:

<!-- In the .csproj -->
<ItemGroup>
  <!-- buildTransitive ensures props/targets flow through transitive dependencies -->
  <None Include="build\MyCompany.Generators.props"
        Pack="true"
        PackagePath="buildTransitive\MyCompany.Generators.props" />
  <None Include="build\MyCompany.Generators.targets"
        Pack="true"
        PackagePath="buildTransitive\MyCompany.Generators.targets" />
</ItemGroup>

Multi-Target Analyzer Package (Analyzer + Library)

When shipping both an analyzer and a runtime library in the same package:

<!-- MyCompany.Widgets.csproj (ships both runtime lib + analyzer) -->
<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFrameworks>net8.0;netstandard2.0</TargetFrameworks>
    <PackageId>MyCompany.Widgets</PackageId>
  </PropertyGroup>

  <!-- Reference generator project, but suppress its output from lib/ -->
  <ItemGroup>
    <ProjectReference Include="..\MyCompany.Widgets.Generators\MyCompany.Widgets.Generators.csproj"
                      OutputItemType="Analyzer"
                      ReferenceOutputAssembly="false" />
  </ItemGroup>
</Project>

NuGet Package Folder Layout

MyCompany.Generators.1.0.0.nupkg
  analyzers/
    dotnet/
      cs/
        MyCompany.Generators.dll          <-- generator/analyzer assembly
  buildTransitive/
    MyCompany.Generators.props            <-- auto-imported MSBuild props
    MyCompany.Generators.targets          <-- auto-imported MSBuild targets
  lib/
    netstandard2.0/
      _._                                <-- empty marker (no runtime lib)

Multi-TFM Packages

Multi-targeting produces a single NuGet package with assemblies for each target framework. Consumers automatically get the best-matching assembly.

When to Multi-Target

Multi-TFM Configuration

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFrameworks>netstandard2.0;net8.0;net9.0</TargetFrameworks>
  </PropertyGroup>

  <!-- API differences per TFM -->
  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
    <PackageReference Include="System.Memory" Version="4.6.0" />
    <PackageReference Include="System.Text.Json" Version="8.0.5" />
  </ItemGroup>
</Project>

Conditional Compilation

public static class StringExtensions
{
    public static bool ContainsIgnoreCase(this string source, string value)
    {
#if NET8_0_OR_GREATER
        return source.Contains(value, StringComparison.OrdinalIgnoreCase);
#else
        return source.IndexOf(value, StringComparison.OrdinalIgnoreCase) >= 0;
#endif
    }
}

NuGet Package Folder Layout (Multi-TFM)

MyCompany.Widgets.1.0.0.nupkg
  lib/
    netstandard2.0/
      MyCompany.Widgets.dll
    net8.0/
      MyCompany.Widgets.dll
    net9.0/
      MyCompany.Widgets.dll

Symbol Packages and Deterministic Builds

Symbol packages (.snupkg) enable source-level debugging for package consumers via the NuGet symbol server.

Enabling Symbol Packages

<PropertyGroup>
  <!-- Generate .snupkg alongside .nupkg -->
  <IncludeSymbols>true</IncludeSymbols>
  <SymbolPackageFormat>snupkg</SymbolPackageFormat>

  <!-- Deterministic builds (required for reproducible packages) -->
  <Deterministic>true</Deterministic>
  <ContinuousIntegrationBuild Condition="'$(CI)' == 'true'">true</ContinuousIntegrationBuild>

  <!-- Embed source in PDB for debugging without source server -->
  <EmbedUntrackedSources>true</EmbedUntrackedSources>
</PropertyGroup>

The snupkg is pushed alongside the nupkg automatically when using dotnet nuget push:

# Push both .nupkg and .snupkg to nuget.org
dotnet nuget push "bin/Release/*.nupkg" \
  --source https://api.nuget.org/v3/index.json \
  --api-key "$NUGET_API_KEY"

SourceLink integration: For source-level debugging with links to the actual source repository, configure SourceLink in your project. See [skill:dotnet-project-structure] for SourceLink setup -- do not duplicate that configuration here.

Embedded PDB Alternative

For packages where a separate symbol package is undesirable:

<PropertyGroup>
  <DebugType>embedded</DebugType>
</PropertyGroup>

This embeds the PDB directly in the assembly DLL. The tradeoff is larger package size but simpler distribution.

Package Signing

NuGet supports author signing (proving package origin) and repository signing (proving it came from a specific feed).

Author Signing with a Certificate

# Sign a package with a PFX certificate
dotnet nuget sign "MyCompany.Widgets.1.0.0.nupkg" \
  --certificate-path ./signing-cert.pfx \
  --certificate-password "$CERT_PASSWORD" \
  --timestamper http://timestamp.digicert.com

# Sign with a certificate from the certificate store (Windows)
dotnet nuget sign "MyCompany.Widgets.1.0.0.nupkg" \
  --certificate-fingerprint "ABC123..." \
  --timestamper http://timestamp.digicert.com

Certificate Requirements

Repository Signing

Repository signing is applied by feed operators (e.g., nuget.org signs all packages). Package authors do not need to configure repository signing -- it is applied automatically by the feed infrastructure.

Verifying Package Signatures

# Verify a signed package
dotnet nuget verify "MyCompany.Widgets.1.0.0.nupkg"

# Verify with verbose output
dotnet nuget verify "MyCompany.Widgets.1.0.0.nupkg" --verbosity detailed

Package Validation

Package validation catches API breaks, invalid package layouts, and compatibility issues before publishing.

Built-in Pack Validation

<PropertyGroup>
  <!-- Enable package validation on dotnet pack -->
  <EnablePackageValidation>true</EnablePackageValidation>
</PropertyGroup>

This validates:

• All TFMs have compatible API surface
• No accidental API removals between package versions
• Package layout follows NuGet conventions

API Compatibility with Baseline Version

Compare the current package against a previously published baseline version to detect breaking changes:

<PropertyGroup>
  <EnablePackageValidation>true</EnablePackageValidation>
  <!-- Compare against last released version -->
  <PackageValidationBaselineVersion>1.0.0</PackageValidationBaselineVersion>
</PropertyGroup>

Microsoft.DotNet.ApiCompat.Task

For advanced API compatibility checking across assemblies:

<ItemGroup>
  <PackageReference Include="Microsoft.DotNet.ApiCompat.Task" Version="8.0.0" PrivateAssets="all" />
</ItemGroup>

<PropertyGroup>
  <!-- Enable API compat analysis -->
  <ApiCompatEnableRuleAttributesMustMatch>true</ApiCompatEnableRuleAttributesMustMatch>
  <ApiCompatEnableRuleCannotChangeParameterName>true</ApiCompatEnableRuleCannotChangeParameterName>
</PropertyGroup>

Suppressing Known Breaks

When intentional API changes are made, generate and commit a suppression file:

# Generate suppression file for known breaks
dotnet pack /p:GenerateCompatibilitySuppressionFile=true

This creates CompatibilitySuppressions.xml:

<!-- CompatibilitySuppressions.xml (committed to source control) -->
<?xml version="1.0" encoding="utf-8"?>
<Suppressions xmlns:ns="https://learn.microsoft.com/dotnet/fundamentals/package-validation/diagnostic-ids">
  <Suppression>
    <DiagnosticId>CP0002</DiagnosticId>
    <Target>M:MyCompany.Widgets.Widget.OldMethod</Target>
    <Left>lib/net8.0/MyCompany.Widgets.dll</Left>
    <Right>lib/net8.0/MyCompany.Widgets.dll</Right>
  </Suppression>
</Suppressions>

Reference the suppression file:

<ItemGroup>
  <ApiCompatSuppressionFile Include="CompatibilitySuppressions.xml" />
</ItemGroup>

NuGet Versioning Strategies

SemVer 2.0 for NuGet

NuGet follows Semantic Versioning 2.0:

Pre-release Suffixes

<!-- Stable release -->
<Version>1.2.3</Version>

<!-- Pre-release with SemVer 2.0 dot-separated suffix -->
<Version>1.2.3-beta.1</Version>

<!-- CI build with commit height (NBGV pattern) -->
<!-- Produces: 1.2.3-beta.42+abcdef -->

NBGV Integration

Nerdbank.GitVersioning (NBGV) calculates versions from git history. For NBGV setup and version.json configuration, see [skill:dotnet-release-management]. This skill covers how NBGV-generated versions interact with NuGet packaging:

<PropertyGroup>
  <!-- NBGV sets Version, PackageVersion, AssemblyVersion automatically -->
  <!-- Do NOT set Version explicitly when using NBGV -->
</PropertyGroup>

NBGV produces versions like 1.2.42-beta+abcdef where:

• 1.2 comes from version.json
• 42 is git commit height
• -beta is the pre-release suffix from version.json
• +abcdef is the git commit hash (build metadata, ignored by NuGet resolution)

Version Properties Reference

Packing and Local Testing

Building the Package

# Pack in Release configuration
dotnet pack --configuration Release

# Pack with specific version override
dotnet pack --configuration Release /p:Version=1.2.3-beta.1

# Output to specific directory
dotnet pack --configuration Release --output ./artifacts

Local Feed Testing

Test a package locally before publishing:

# Create a local feed directory
mkdir -p ~/local-nuget-feed

# Add the package to the local feed
dotnet nuget push "bin/Release/MyCompany.Widgets.1.0.0.nupkg" \
  --source ~/local-nuget-feed

# In the consuming project, add the local feed
dotnet nuget add source ~/local-nuget-feed --name LocalFeed

Package Content Inspection

# List package contents (nupkg is a zip file)
unzip -l MyCompany.Widgets.1.0.0.nupkg

# Verify analyzer placement
unzip -l MyCompany.Generators.1.0.0.nupkg | grep analyzers/

Agent Gotchas

1. Do not set both PackageLicenseExpression and PackageLicenseFile -- they are mutually exclusive. Use PackageLicenseExpression for standard SPDX identifiers, PackageLicenseFile for custom licenses only.

2. Source generators MUST target netstandard2.0 -- the Roslyn host requires this. Do not multi-target generators themselves; multi-target the runtime library that references the generator project.

3. Do not set IncludeBuildOutput to false on library projects -- only on pure analyzer/generator projects that should not contribute runtime assemblies.

4. buildTransitive vs build folder -- use buildTransitive for props/targets that should flow through transitive PackageReference dependencies. The build folder only affects direct consumers.

5. Package validation suppression uses ApiCompatSuppressionFile with CompatibilitySuppressions.xml -- not a PackageValidationSuppression MSBuild item. Generate the file with /p:GenerateCompatibilitySuppressionFile=true.

6. SDK-style projects auto-include all *.cs files -- adding TFM-conditional Compile Include without a preceding Compile Remove causes NETSDK1022 duplicate items.

7. Never hardcode API keys in CLI examples -- always use environment variable placeholders ($NUGET_API_KEY) with a note about CI secret storage.

8. ContinuousIntegrationBuild must be conditional on CI -- setting it unconditionally breaks local debugging by making PDBs non-reproducible with local file paths.