Imported from ShawnDelaineBellazanLoop/PMCR-O-Marketplace (.pmcro/skills-staging/dotnet-msbuild/msbuild-antipatterns/SKILL.md). Install upstream with npx skills add ShawnDelaineBellazanLoop/PMCR-O-Marketplace --skill msbuild-antipatterns. Copyright stays with the author (MIT).

MSBuild Anti-Pattern Catalog

A numbered catalog of common MSBuild anti-patterns. Each entry follows the format:

• Smell: What to look for
• Why it's bad: Impact on builds, maintainability, or correctness
• Fix: Concrete transformation

Use this catalog when scanning project files for improvements.

AP-01: <Exec> for Operations That Have Built-in Tasks

Smell: <Exec Command="mkdir ..." />, <Exec Command="copy ..." />, <Exec Command="del ..." />

Why it's bad: Built-in tasks are cross-platform, support incremental build, emit structured logging, and handle errors consistently. <Exec> is opaque to MSBuild.

<!-- BAD -->
<Target Name="PrepareOutput">
  <Exec Command="mkdir $(OutputPath)logs" />
  <Exec Command="copy config.json $(OutputPath)" />
  <Exec Command="del $(IntermediateOutputPath)*.tmp" />
</Target>

<!-- GOOD -->
<Target Name="PrepareOutput">
  <MakeDir Directories="$(OutputPath)logs" />
  <Copy SourceFiles="config.json" DestinationFolder="$(OutputPath)" />
  <Delete Files="@(TempFiles)" />
</Target>

Built-in task alternatives:

AP-02: Unquoted Condition Expressions

Smell: Condition="$(Foo) == Bar" — either side of a comparison is unquoted.

Why it's bad: If the property is empty or contains spaces/special characters, the condition evaluates incorrectly or throws a parse error. MSBuild requires single-quoted strings for reliable comparisons.

<!-- BAD -->
<PropertyGroup Condition="$(Configuration) == Release">
  <Optimize>true</Optimize>
</PropertyGroup>

<!-- GOOD -->
<PropertyGroup Condition="'$(Configuration)' == 'Release'">
  <Optimize>true</Optimize>
</PropertyGroup>

Rule: Always quote both sides of == and != comparisons with single quotes.

AP-03: Hardcoded Absolute Paths

Smell: Paths like C:\tools\, D:\packages\, /usr/local/bin/ in project files.

Why it's bad: Breaks on other machines, CI environments, and other operating systems. Not relocatable.

<!-- BAD -->
<PropertyGroup>
  <ToolPath>C:\tools\mytool\mytool.exe</ToolPath>
</PropertyGroup>
<Import Project="C:\repos\shared\common.props" />

<!-- GOOD -->
<PropertyGroup>
  <ToolPath>$(MSBuildThisFileDirectory)tools\mytool\mytool.exe</ToolPath>
</PropertyGroup>
<Import Project="$(RepoRoot)eng\common.props" />

Preferred path properties:

AP-04: Restating SDK Defaults

Smell: Properties set to values that the .NET SDK already provides by default.

Why it's bad: Adds noise, hides intentional overrides, and makes it harder to identify what's actually customized. When defaults change in newer SDKs, the redundant properties may silently pin old behavior.

<!-- BAD: All of these are already the default -->
<PropertyGroup>
  <OutputType>Library</OutputType>
  <EnableDefaultItems>true</EnableDefaultItems>
  <EnableDefaultCompileItems>true</EnableDefaultCompileItems>
  <RootNamespace>MyLib</RootNamespace>       <!-- matches project name -->
  <AssemblyName>MyLib</AssemblyName>         <!-- matches project name -->
  <AppendTargetFrameworkToOutputPath>true</AppendTargetFrameworkToOutputPath>
</PropertyGroup>

<!-- GOOD: Only non-default values -->
<PropertyGroup>
  <TargetFramework>net8.0</TargetFramework>
</PropertyGroup>

AP-05: Manual File Listing in SDK-Style Projects

Smell: <Compile Include="File1.cs" />, <Compile Include="File2.cs" /> in SDK-style projects.

Why it's bad: SDK-style projects automatically glob **/*.cs (and other file types). Explicit listing is redundant, creates merge conflicts, and new files may be accidentally missed if not added to the list.

<!-- BAD -->
<ItemGroup>
  <Compile Include="Program.cs" />
  <Compile Include="Services\MyService.cs" />
  <Compile Include="Models\User.cs" />
</ItemGroup>

<!-- GOOD: Remove entirely — SDK includes all .cs files by default.
     Only use Remove/Exclude when you need to opt out: -->
<ItemGroup>
  <Compile Remove="LegacyCode\**" />
</ItemGroup>

Exception: Non-SDK-style (legacy) projects require explicit file includes. If migrating, see msbuild-modernization skill.

Exception (F# / .fsproj): F# compilation is order-dependent — the compiler processes <Compile Include> items sequentially and a file can only reference types/modules declared in files listed above it. .fsproj files must therefore list every source file explicitly, in dependency order (utility/leaf modules at the top, the entry point such as Program.fs at the bottom). If a .fsi signature file is used, it must appear immediately before its companion .fs implementation file.

AP-06: Using <Reference> with HintPath for NuGet Packages

Smell: <Reference Include="..." HintPath="..\packages\SomePackage\lib\..." />

Why it's bad: This is the legacy packages.config pattern. It doesn't support transitive dependencies, version conflict resolution, or automatic restore. The packages/ folder must be committed or restored separately.

<!-- BAD -->
<ItemGroup>
  <Reference Include="Newtonsoft.Json">
    <HintPath>..\packages\Newtonsoft.Json.13.0.3\lib\netstandard2.0\Newtonsoft.Json.dll</HintPath>
  </Reference>
</ItemGroup>

<!-- GOOD -->
<ItemGroup>
  <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
</ItemGroup>

Note: <Reference> without HintPath is still valid for .NET Framework GAC assemblies like WindowsBase, PresentationCore, etc.

AP-07: Missing PrivateAssets="all" on Analyzer/Tool Packages

Smell: <PackageReference Include="StyleCop.Analyzers" Version="..." /> without PrivateAssets="all".

Why it's bad: Without PrivateAssets="all", analyzer and build-tool packages flow as transitive dependencies to consumers of your library. Consumers get unwanted analyzers or build-time tools they didn't ask for.

See references/private-assets.md for BAD/GOOD examples and the full list of packages that need this.

AP-08: Copy-Pasted Properties Across Multiple .csproj Files

Smell: The same <PropertyGroup> block appears in 3+ project files.

Why it's bad: Maintenance burden — a change must be made in every file. Inconsistencies creep in over time.

<!-- BAD: Repeated in every .csproj -->
<!-- ProjectA.csproj, ProjectB.csproj, ProjectC.csproj all have: -->
<PropertyGroup>
  <Nullable>enable</Nullable>
  <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
  <ImplicitUsings>enable</ImplicitUsings>
</PropertyGroup>

<!-- GOOD: Define once in Directory.Build.props at the repo/src root -->
<!-- Directory.Build.props -->
<Project>
  <PropertyGroup>
    <Nullable>enable</Nullable>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>
</Project>

See directory-build-organization skill for full guidance on structuring Directory.Build.props / Directory.Build.targets.

AP-09: Scattered Package Versions Without Central Package Management

Smell: <PackageReference Include="X" Version="1.2.3" /> with different versions of the same package across projects.

Why it's bad: Version drift — different projects use different versions of the same package, leading to runtime mismatches, unexpected behavior, or diamond dependency conflicts.

<!-- BAD: Version specified in each project, can drift -->
<!-- ProjectA.csproj -->
<PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
<!-- ProjectB.csproj -->
<PackageReference Include="Newtonsoft.Json" Version="13.0.3" />

Fix: Use Central Package Management. See https://learn.microsoft.com/en-us/nuget/consume-packages/central-package-management for details.

AP-10: Monolithic Targets (Too Much in One Target)

Smell: A single <Target> with 50+ lines doing multiple unrelated things.

Why it's bad: Can't skip individual steps via incremental build, hard to debug, hard to extend, and the target name becomes meaningless.

<!-- BAD -->
<Target Name="PrepareRelease" BeforeTargets="Build">
  <WriteLinesToFile File="version.txt" Lines="$(Version)" Overwrite="true" />
  <Copy SourceFiles="LICENSE" DestinationFolder="$(OutputPath)" />
  <Exec Command="signtool sign /f cert.pfx $(OutputPath)*.dll" />
  <MakeDir Directories="$(OutputPath)docs" />
  <Copy SourceFiles="@(DocFiles)" DestinationFolder="$(OutputPath)docs" />
  <!-- ... 30 more lines ... -->
</Target>

<!-- GOOD: Single-responsibility targets -->
<Target Name="WriteVersionFile" BeforeTargets="CoreCompile"
        Inputs="$(MSBuildProjectFile)" Outputs="$(IntermediateOutputPath)version.txt">
  <WriteLinesToFile File="$(IntermediateOutputPath)version.txt" Lines="$(Version)" Overwrite="true" />
</Target>

<Target Name="CopyLicense" AfterTargets="Build">
  <Copy SourceFiles="LICENSE" DestinationFolder="$(OutputPath)" SkipUnchangedFiles="true" />
</Target>

<Target Name="SignAssemblies" AfterTargets="Build" DependsOnTargets="CopyLicense"
        Condition="'$(SignAssemblies)' == 'true'">
  <Exec Command="signtool sign /f cert.pfx %(AssemblyFiles.Identity)" />
</Target>

AP-11: Custom Targets Missing Inputs and Outputs

Smell: <Target Name="MyTarget" BeforeTargets="Build"> with no Inputs / Outputs attributes.

Why it's bad: The target runs on every build, even when nothing changed. This defeats incremental build and slows down no-op builds.

See references/incremental-build-inputs-outputs.md for BAD/GOOD examples and the full pattern including FileWrites registration.

See incremental-build skill for deep guidance on Inputs/Outputs, FileWrites, and up-to-date checks.

AP-12: Setting Defaults in .targets Instead of .props

Smell: <PropertyGroup> with default values inside a .targets file.

Why it's bad: .targets files are imported late (after project files). By the time they set defaults, other .targets files may have already used the empty/undefined value. .props files are imported early and are the correct place for defaults.

<!-- BAD: custom.targets -->
<PropertyGroup>
  <MyToolVersion>2.0</MyToolVersion>
</PropertyGroup>
<Target Name="RunMyTool">
  <Exec Command="mytool --version $(MyToolVersion)" />
</Target>

<!-- GOOD: Split into .props (defaults) + .targets (logic) -->
<!-- custom.props (imported early) -->
<PropertyGroup>
  <MyToolVersion Condition="'$(MyToolVersion)' == ''">2.0</MyToolVersion>
</PropertyGroup>

<!-- custom.targets (imported late) -->
<Target Name="RunMyTool">
  <Exec Command="mytool --version $(MyToolVersion)" />
</Target>

Rule: .props = defaults and settings (evaluated early). .targets = build logic and targets (evaluated late).

AP-13: Import Without Exists() Guard

Smell: <Import Project="some-file.props" /> without a Condition="Exists('...')" check.

Why it's bad: If the file doesn't exist (not yet created, wrong path, deleted), the build fails with a confusing error. Optional imports should always be guarded.

<!-- BAD -->
<Import Project="$(RepoRoot)eng\custom.props" />

<!-- GOOD: Guard optional imports -->
<Import Project="$(RepoRoot)eng\custom.props" Condition="Exists('$(RepoRoot)eng\custom.props')" />

<!-- ALSO GOOD: Sdk attribute imports don't need guards (they're required by design) -->
<Project Sdk="Microsoft.NET.Sdk">

Exception — required imports: Imports that are required for the build to work correctly should fail fast — don't guard those. Guard imports that are optional or environment-specific (e.g., local developer overrides, CI-specific settings).

Exception — NuGet package forwarders: .props/.targets files inside a NuGet package's per-TFM build/ or buildTransitive/ folder routinely import a sibling file under buildTransitive/<tfm>/… without an Exists() guard. These are a package contract: the target file is guaranteed to be present in the restored package, even if it doesn't appear in the source tree at that relative path. The package layout is typically produced by:

• A custom .nuspec with per-TFM <file> entries — e.g. <file src="buildTransitive\common\MyAdapter.props" target="buildTransitive\net8.0\MyAdapter.props" /> — that copy files from a single source folder (such as buildTransitive/common/) into per-TFM subfolders at pack time, or
• <None Update="..."> / <Content Include="..."> items in the .csproj with a per-TFM <PackagePath> (e.g. <PackagePath>buildTransitive/net8.0/</PackagePath>), declared once per target TFM, or
• SDK conventions (e.g. IncludeBuildOutput, BuildOutputTargetFolder) that place built outputs under build/<tfm>/.

Before flagging an unguarded <Import> inside a build/ or buildTransitive/ folder, resolve it against the packed layout — read every *.nuspec in the project directory and its immediate parent directory (shared nuspecs are common in mono-repos; do not walk further up), and any <PackagePath> metadata on <None>/<Content> items in the .csproj. Only flag if the target path is missing from both the source tree and the projected package layout. The dotnet-msbuild/extension-points skill — Source tree vs packed layout — documents the full cross-check procedure.

Forwarding buildTransitive/ → build/: forward through the sibling build/*.props / build/*.targets file (not directly to buildMultiTargeting/); when build/ is per-TFM (build/<tfm>/), include the TFM segment derived from the file's own folder (not $(TargetFramework)), or transitive consumers hit MSB4019. See the extension-points skill — Forwarding chain — for the rule and derivation expression.

AP-14: Backslashes in Paths — Where It Matters

Smell: Backslash path separators in .props/.targets files meant to run cross-platform.

Where this is a real bug (🔴 Error) — paths that MSBuild does not route through its path normalizer:

• Raw shell strings inside <Exec Command="...\tools\foo.exe ..." /> — passed verbatim to bash/sh on Unix, which treats \ as an escape.
• Backslash-delimited paths inside CDATA blocks, embedded in source files written by <WriteLinesToFile>, or constructed for non-MSBuild consumers (custom scripts, response files, environment variables).
• Paths handed to custom tasks that call OS file APIs directly without going through MSBuild path utilities.

Where this is only a style preference (🔵 Style) — paths that go through MSBuild's evaluator (<Import Project="...">, file-path properties consumed by built-in tasks like <Copy>/<MakeDir>/<Delete>, item Include=/Exclude= globs):

MSBuild's evaluator normalizes \ → / on Unix-like systems before resolving the path. See FileUtilities.MaybeAdjustFilePath and ConvertToUnixSlashes in microsoft/msbuild src/Framework/FileUtilities.cs. So <Import Project="$(MSBuildThisFileDirectory)..\..\build\common.props" /> resolves correctly on Linux/macOS today. Forward slashes are still preferred for consistency, but the import will not break and existing backslash-style imports should not be flagged as 🔴 Error.

<!-- 🔴 Error: \ in raw shell string breaks on Linux/macOS -->
<Exec Command="$(MSBuildThisFileDirectory)tools\release\sign.exe $(OutputPath)" />

<!-- 🔵 Style: \ in Import is normalized on Unix, but / is nicer -->
<Import Project="$(MSBuildThisFileDirectory)..\..\build\common.props" />

<!-- ✅ Recommended in new code -->
<Import Project="$(MSBuildThisFileDirectory)../../build/common.props" />

Verification rule: Before flagging a backslash path as 🔴 Error, ask "does this string flow through MSBuild's evaluator, or is it handed verbatim to a non-MSBuild consumer?" Only the second case is a correctness defect.

Note: $(MSBuildThisFileDirectory) already ends with a platform-appropriate separator, so $(MSBuildThisFileDirectory)tools/mytool works on both platforms.

AP-15: Unconditional Property Override in Multiple Scopes

Smell: A property set unconditionally in both Directory.Build.props and a .csproj — last write wins silently.

Why it's bad: Hard to trace which value is actually used. Makes the build fragile and confusing for anyone reading the project files.

<!-- BAD: Directory.Build.props sets it, csproj silently overrides -->
<!-- Directory.Build.props -->
<PropertyGroup>
  <OutputPath>bin\custom\</OutputPath>
</PropertyGroup>
<!-- MyProject.csproj -->
<PropertyGroup>
  <OutputPath>bin\other\</OutputPath>
</PropertyGroup>

<!-- GOOD: Use a condition so overrides are intentional -->
<!-- Directory.Build.props -->
<PropertyGroup>
  <OutputPath Condition="'$(OutputPath)' == ''">bin\custom\</OutputPath>
</PropertyGroup>
<!-- MyProject.csproj can now intentionally override or leave the default -->

For additional anti-patterns (AP-16 through AP-23) and a quick-reference checklist, see additional-antipatterns.md.