diff --git a/.github/workflows/test-tools.yml b/.github/workflows/test-tools.yml
index c792dc7..6b675c3 100644
--- a/.github/workflows/test-tools.yml
+++ b/.github/workflows/test-tools.yml
@@ -6,18 +6,26 @@
 # all: PR #131 reported zero. That left every runner regression test inert, including the
 # one added in #131 to stop the System.Drawing.Common reference being dropped as unused.
 #
-# Two jobs, deliberately separate.
+# Two jobs and two ComplianceRunner test projects, deliberately separate.
 #
 #   dotnet-tests       Hermetic. Checkout, SDK, run. No network beyond NuGet, no BHoM.
+#                      SerialiserRunner, VersioningRunner and Compliance.Unit.Tests.
 #   compliance-tests   Resolves the Test_Toolkit dependency graph first, so Compliance.Tests
 #                      can compile and its entry-point tests can run.
 #
+# Why the ComplianceRunner suite is split across two projects. Compliance.Unit.Tests compiles
+# Annotation.cs, ArgParser.cs, FileFilter.cs and SarifBuilder.cs directly instead of
+# project-referencing Compliance.Shared, so it pulls in no BHoM assembly and runs in the
+# hermetic job with nothing installed. Compliance.Tests holds everything that cannot: the three
+# unit files that take a BHoM type as a parameter, and the integration files that invoke the
+# built runner executables.
+#
 # Why Compliance.Tests needs the second job. Compliance.Shared HintPaths five assemblies out
 # of C:\ProgramData\BHoM\Assemblies. Measured on a machine carrying the BHoM installer, four
 # resolve and only CodeComplianceTest_oM.dll is missing, because it is built by
 # BHoM/Test_Toolkit (CodeCompliance_oM/CodeComplianceTest_oM.csproj) rather than shipped in
 # the installer payload. AnnotationConvert.cs then fails CS0234 on BH.oM.Test.CodeCompliance
-# and takes the whole project down, which is why all nine of its test files were inert.
+# and takes the whole project down.
 #
 # resolve-dependencies in mode: seeds with seed BHoM/Test_Toolkit is exactly what ci-compliance
 # already does before prepare-runner publishes ComplianceRunner, and ComplianceRunner.csproj
@@ -58,10 +66,14 @@ jobs:
       - name: Checkout
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
+      # Two versions: the Serialiser and Versioning suites target net8.0-windows, matching
+      # their runners; Compliance.Unit.Tests targets net10.0, matching ComplianceRunner.
       - name: Set up .NET
         uses: actions/setup-dotnet@c2fa09f4bde5ebb9d1777cf28262a3eb3db3ced7 # v5
         with:
-          dotnet-version: '8.0'
+          dotnet-version: |
+            8.0
+            10.x
 
       - name: SerialiserRunner tests
         run: dotnet test tools/SerialiserRunner/src/SerialiserRunner.Tests --nologo
@@ -69,6 +81,9 @@ jobs:
       - name: VersioningRunner tests
         run: dotnet test tools/VersioningRunner/src/VersioningRunner.Tests --nologo
 
+      - name: ComplianceRunner unit tests (BHoM-free)
+        run: dotnet test tools/ComplianceRunner/tests/Compliance.Unit.Tests --nologo
+
   # ComplianceRunner's own suite, including the entry-point characterisation tests. Needs
   # CodeComplianceTest_oM.dll, so it builds the Test_Toolkit graph first. See the header.
   compliance-tests:
diff --git a/tools/ComplianceRunner/Platform.slnx b/tools/ComplianceRunner/Platform.slnx
index da5e1f2..2470a6a 100644
--- a/tools/ComplianceRunner/Platform.slnx
+++ b/tools/ComplianceRunner/Platform.slnx
@@ -3,4 +3,5 @@
   <Project Path="src/DatasetComplianceRunner/DatasetComplianceRunner.csproj" Id="073f2c91-6a2b-4af2-91f8-a6b1fffe5c91" />
   <Project Path="src/Shared/Compliance.Shared/Compliance.Shared.csproj" Id="a2ff49f5-c2db-4687-b981-e48539def63f" />
   <Project Path="tests/Compliance.Tests/Compliance.Tests.csproj" />
+  <Project Path="tests/Compliance.Unit.Tests/Compliance.Unit.Tests.csproj" />
 </Solution>
diff --git a/tools/ComplianceRunner/tests/Compliance.Tests/Compliance.Tests.csproj b/tools/ComplianceRunner/tests/Compliance.Tests/Compliance.Tests.csproj
index ca84fae..a5bd949 100644
--- a/tools/ComplianceRunner/tests/Compliance.Tests/Compliance.Tests.csproj
+++ b/tools/ComplianceRunner/tests/Compliance.Tests/Compliance.Tests.csproj
@@ -20,11 +20,30 @@
     <ProjectReference Include="..\..\src\Shared\Compliance.Shared\Compliance.Shared.csproj" />
   </ItemGroup>
 
+  <!--
+    This project holds the BHoM-DEPENDENT half of the suite. It runs in test-tools.yml's
+    compliance-tests job, which resolves the Test_Toolkit dependency graph first so that
+    CodeComplianceTest_oM.dll exists and this project can compile. The BHoM-free half moved
+    to ../Compliance.Unit.Tests, which runs in the hermetic dotnet-tests job instead and
+    needs nothing installed.
+
+    What is left here and why each item cannot move:
+      Unit/CheckMetadataTests.cs    CheckMetadata.GetOutput takes a BH.oM.Test.TestStatus.
+      Unit/OutputEmitterTests.cs    OutputEmitter.Write takes a BH.oM.Test.TestStatus.
+      Unit/AnnotationConvertTests.cs  Constructs BH.oM.Test.CodeCompliance.Error and
+                                      exercises the ITestInformation conversion path.
+      Integration/*                 Invoke the built runner executables against real engines.
+
+    Note the boundary is NOT unit-versus-integration: three of the six original unit test
+    files are BHoM-dependent. For CheckMetadata and OutputEmitter the whole dependency is a
+    single enum parameter, which is thin but real, and narrowing it would mean changing
+    production signatures.
+  -->
+
   <ItemGroup>
     <!--
       BHoM assemblies required at compile-time (for TestStatus in CheckMetadataTests)
       and by integration tests that invoke the runner executables against real BHoM engines.
-      Structural unit tests (SarifBuilder, ArgParser, FileFilter) do not need BHoM at runtime.
     -->
     <Reference Include="BHoM">
       <HintPath>$(ProgramData)\BHoM\Assemblies\BHoM.dll</HintPath>
diff --git a/tools/ComplianceRunner/tests/Compliance.Tests/Integration/PathspecFilterPairingTests.cs b/tools/ComplianceRunner/tests/Compliance.Tests/Integration/PathspecFilterPairingTests.cs
index d27bd03..a96dc1d 100644
--- a/tools/ComplianceRunner/tests/Compliance.Tests/Integration/PathspecFilterPairingTests.cs
+++ b/tools/ComplianceRunner/tests/Compliance.Tests/Integration/PathspecFilterPairingTests.cs
@@ -11,7 +11,8 @@
 ///   2. ComplianceRunner then asks FileFilter.IsRelevantFile of every file it was handed.
 ///
 /// Each half has tests. `.github/scripts/tests/test-changed-file-patterns.sh` asserts the
-/// pathspec behaviour against real git, and FileFilterTests asserts the predicate. Neither
+/// pathspec behaviour against real git, and FileFilterTests, which lives in the sibling
+/// Compliance.Unit.Tests project, asserts the predicate. Neither
 /// asserts that the two agree, and they do not: the pathspec token `*AssemblyInfo.cs` selects
 /// any file whose name ENDS with that string, while FileFilter.cs:24 requires the name to
 /// EQUAL it. A file in between is selected, counted into the skip decision, handed to the
@@ -20,9 +21,9 @@
 /// These tests are written to PASS against today's behaviour. They record the disagreement so
 /// it is visible in the suite. Whether the fix narrows the pathspec or widens the filter is
 /// open: BHoMBot used EndsWith("AssemblyInfo.cs") (ProjectCompliance.cs:33), so widening the
-/// filter restores the older semantics, and FileFilterTests.cs:20 currently asserts the
-/// narrower one deliberately. Where an assertion would change under one of those two answers,
-/// the comment says what it should become and under which answer.
+/// filter restores the older semantics, and line 20 of that same FileFilterTests file asserts
+/// the narrower one deliberately. Where an assertion would change under one of those two
+/// answers, the comment says what it should become and under which answer.
 /// </summary>
 [TestFixture]
 [Category("Integration")]
diff --git a/tools/ComplianceRunner/tests/Compliance.Unit.Tests/Compliance.Unit.Tests.csproj b/tools/ComplianceRunner/tests/Compliance.Unit.Tests/Compliance.Unit.Tests.csproj
new file mode 100644
index 0000000..d40cb78
--- /dev/null
+++ b/tools/ComplianceRunner/tests/Compliance.Unit.Tests/Compliance.Unit.Tests.csproj
@@ -0,0 +1,57 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <!--
+    The BHoM-free half of the ComplianceRunner test suite, split out so it can run in CI.
+
+    Compliance.Tests cannot compile without a BHoM install AND a built Test_Toolkit: its
+    ProjectReference to Compliance.Shared drags in AnnotationConvert.cs, which needs
+    BH.oM.Test.CodeCompliance from CodeComplianceTest_oM.dll. That assembly ships with
+    Test_Toolkit, not with the installer payload, so even a machine with BHoM installed
+    cannot build it. Result: every test in that project has been inert since it was written.
+
+    This project deliberately has NO ProjectReference to Compliance.Shared. It compiles the
+    four source files that reference no BHoM type directly into the test assembly, so it
+    builds and runs on a bare runner with no BHoM install and no Test_Toolkit.
+
+    Those four files were verified free of BHoM types by reading them, not by their names:
+    every "BHoM" occurrence in them is a comment or a string literal (e.g. the "BHoM.<check>"
+    SARIF ruleId prefix). The three excluded source files have real dependencies:
+    CheckMetadata and OutputEmitter take a BH.oM.Test.TestStatus parameter, and
+    AnnotationConvert consumes BH.oM.Test.CodeCompliance.Error and ITestInformation.
+
+    NUnit rather than the xUnit used by SerialiserRunner.Tests and VersioningRunner.Tests.
+    The three test files here were moved verbatim from Compliance.Tests, which is an NUnit
+    project; rewriting ~350 lines of assertions into xUnit would risk changing what they
+    assert, and the point of this change is to find out what they do assert. Harmonising the
+    two frameworks is a separate decision.
+  -->
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <RootNamespace>Compliance.Tests</RootNamespace>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="NUnit"                  Version="3.14.0" />
+    <PackageReference Include="NUnit3TestAdapter"      Version="4.6.0" />
+    <PackageReference Include="NUnit.Analyzers"        Version="3.6.1" />
+    <PackageReference Include="coverlet.collector"     Version="6.0.2" />
+  </ItemGroup>
+
+  <!--
+    Source under test, linked rather than project-referenced. Keep this list in step with
+    Compliance.Shared: a new file there that references no BHoM type belongs here too, and
+    one that does must not be added or this project stops building on a bare runner.
+  -->
+  <ItemGroup>
+    <Compile Include="..\..\src\Shared\Compliance.Shared\Annotation.cs"   Link="Linked\Annotation.cs" />
+    <Compile Include="..\..\src\Shared\Compliance.Shared\ArgParser.cs"    Link="Linked\ArgParser.cs" />
+    <Compile Include="..\..\src\Shared\Compliance.Shared\FileFilter.cs"   Link="Linked\FileFilter.cs" />
+    <Compile Include="..\..\src\Shared\Compliance.Shared\SarifBuilder.cs" Link="Linked\SarifBuilder.cs" />
+  </ItemGroup>
+
+</Project>
diff --git a/tools/ComplianceRunner/tests/Compliance.Tests/Unit/ArgParserTests.cs b/tools/ComplianceRunner/tests/Compliance.Unit.Tests/Unit/ArgParserTests.cs
similarity index 100%
rename from tools/ComplianceRunner/tests/Compliance.Tests/Unit/ArgParserTests.cs
rename to tools/ComplianceRunner/tests/Compliance.Unit.Tests/Unit/ArgParserTests.cs
diff --git a/tools/ComplianceRunner/tests/Compliance.Tests/Unit/FileFilterTests.cs b/tools/ComplianceRunner/tests/Compliance.Unit.Tests/Unit/FileFilterTests.cs
similarity index 100%
rename from tools/ComplianceRunner/tests/Compliance.Tests/Unit/FileFilterTests.cs
rename to tools/ComplianceRunner/tests/Compliance.Unit.Tests/Unit/FileFilterTests.cs
diff --git a/tools/ComplianceRunner/tests/Compliance.Tests/Unit/SarifBuilderTests.cs b/tools/ComplianceRunner/tests/Compliance.Unit.Tests/Unit/SarifBuilderTests.cs
similarity index 100%
rename from tools/ComplianceRunner/tests/Compliance.Tests/Unit/SarifBuilderTests.cs
rename to tools/ComplianceRunner/tests/Compliance.Unit.Tests/Unit/SarifBuilderTests.cs