Getting started

Install

Mutato ships as a .NET global tool. Because .NET 10 packaging is platform-specific, the tool is installed per RID behind the dotnet-mutato manifest package:

dotnet tool install -g dotnet-mutato --prerelease

The optional test-side hooks live in a separate package (see Cooperative hooks):

# added for you by `mutato init`, or reference it manually
dotnet add test/YourProject.Tests package Mutato.Testing --prerelease

Build from source

To run against the current source tree instead of a published package:

git clone https://github.com/slang25/mutation-testing-play
cd mutation-testing-play

dotnet pack src/Mutato.Cli -c Release        # -> artifacts/dotnet-mutato.<rid>.*.nupkg
dotnet pack src/Mutato.Testing -c Release    # -> artifacts/Mutato.Testing.*.nupkg (+ Runtime)
dotnet tool install -g --add-source artifacts dotnet-mutato --prerelease

Run it

From the root of the repository you want to test:

mutato init      # discover the target/test pair, add the Mutato.Testing hooks,
                 # and write a mutation-config.json
mutato           # your first mutation score

mutato also works without init — the hooks package is optional, and there is nothing to deploy alongside your tests: the runtime is compiled into the instrumented target as injected source.

With no --project/--tests, Mutato reads ./mutation-config.json if present, otherwise auto-discovers the target and test project pair under the current directory (preferring test projects that reference Mutato.Testing).

Explicit invocation

You can also point Mutato at specific projects and narrow what it mutates:

mutato \
  --project src/Polly.Core/Polly.Core.csproj \
  --tests-project test/Polly.Core.Tests/Polly.Core.Tests.csproj \
  --filter Polly.Retry.RetryHelper \
  --workers 4 \
  --json report.json \
  --html report.html

• --filter scopes mutation to a type or namespace prefix — start narrow.
• --tests-project builds the test project and locates its assembly; pass a prebuilt --tests <tests.dll> to skip the build.
• --json / --html emit a Stryker-schema report you can open in the standard viewer.

See Configuration for the full set of options and the mutation-config.json file format.

From MSBuild

If your test project references the Mutato.Testing package, a run is also available as an MSBuild target:

dotnet build test/YourProject.Tests /t:Mutate