How do I prevent dotnet:NETSDK1022 in CI?

Keep SDK-style project files minimal and rely on defaults where possible. Validate migrations in CI with a clean build rather than incremental state.

How can I manually validate dotnet:NETSDK1022?

Re-run the failing command and confirm the original code/message is gone. Confirm expected artifacts or outputs exist (packages restored, build/publish succeeds).

NETSDK1022: Duplicate items were included

Fix it fast

Most likely: The project explicitly includes files that SDK-style projects already include automatically, usually duplicate Compile, Content, or None items.

1. Confirm this is your error

error NETSDK1022: Duplicate 'Content' items were included. The duplicate items were: 'appsettings.json'

2. Check the cause

dotnet build -v minimal
grep -n "<Compile\|<Content\|<None\|EnableDefault" *.csproj
dotnet msbuild -preprocess:project.preprocessed.xml

3. Apply the safe fix

# Best fix: remove the explicit duplicate Include from the project file and rely on SDK defaults.
# Look for the duplicate filename from the NETSDK1022 message in .csproj, .props, or .targets files.

# Only if you intentionally manage every item manually, disable the relevant default item group.
# Example properties: EnableDefaultCompileItems=false, EnableDefaultContentItems=false, EnableDefaultNoneItems=false
dotnet build

4. Verify it works

dotnet build
dotnet msbuild -preprocess:project.preprocessed.xml

Don't use unsafe shortcuts

Do not disable all default items just to fix one duplicate unless the project intentionally manages every item manually.
Do not keep old explicit globs after migrating to an SDK-style project.
Do not fix only the visible project file if imported .props or .targets files add the duplicate.

What Broke in the Build

The project explicitly includes files that SDK-style projects already include by default, creating duplicate items.

Fix the underlying build failure

Remove redundant Compile or Content entries from the project file, which is usually the best fix, or disable the relevant defaults with EnableDefault*Items=false if you want full manual control, and rebuild with dotnet build.

Validation

Re-run the failing command and confirm the original code/message is gone, and confirm expected artifacts or outputs exist (packages restored, build/publish succeeds).

Why the Build Fails

Usually this comes down to leftover explicit globbing remains after migrating to an SDK-style project, custom includes overlap with the SDK defaults, or imported props or targets add the same items twice.

Prove the Build Path Is Clean

dotnet build succeeds without NETSDK1022.

The duplicated file appears only once in the evaluated build items or binlog.

Mechanism

SDK-style projects add Compile and Content items automatically from the project directory. Explicit ItemGroup entries that overlap those defaults trigger NETSDK1022.

Keep Build Prerequisites Consistent

To prevent this, keep SDK-style project files minimal and rely on defaults where possible, and validate migrations in CI with a clean build rather than incremental state.

Docs and source code

NETSDK1022 message template

User-facing message template explaining default includes. - GitHub

  <data name="DuplicateItemsError" xml:space="preserve">
    <value>NETSDK1022: Duplicate '{0}' items were included. The .NET SDK includes '{0}' items from your project directory by default. You can either remove these items from your project file, or set the '{1}' property to '{2}' if you want to explicitly include them in your project file. For more information, see {4}. The duplicate items were: {3}</value>
    <comment>{StrBegins="NETSDK1022: "}</comment>
  </data>