diff --git a/tests/test_skill_eval_optional_dependencies.py b/tests/test_skill_eval_optional_dependencies.py
new file mode 100644
index 00000000..3a243090
--- /dev/null
+++ b/tests/test_skill_eval_optional_dependencies.py
@@ -0,0 +1,83 @@
+"""Lightweight controllers must remain usable without the optional skills parser."""
+
+import subprocess
+import sys
+import textwrap
+import unittest
+from pathlib import Path
+
+
+class OptionalSkillsDependencyTests(unittest.TestCase):
+    def run_without_yaml(self, source):
+        root = Path(__file__).resolve().parents[1]
+        script = (
+            f"import sys; sys.path[:0] = {[str(root), str(root / 'src')]!r}\n"
+            "sys.modules['yaml'] = None\n"
+            + textwrap.dedent(source)
+        )
+        result = subprocess.run(
+            [sys.executable, "-I", "-S", "-c", script],
+            capture_output=True, text=True, check=False,
+        )
+        self.assertEqual(result.returncode, 0, result.stderr)
+
+    def test_comparison_reporting_without_yaml(self):
+        self.run_without_yaml("""
+            from tools.skill_eval_compare import condition_summary, read_report
+
+            summary = condition_summary([])
+            assert set(summary) == {'baseline', 'candidate'}
+            assert all(item['input_tokens'] is None for item in summary.values())
+            assert callable(read_report)
+            assert 'inferrsi.skill_catalog' not in sys.modules
+        """)
+
+    def test_checkpoint_without_yaml(self):
+        self.run_without_yaml("""
+            from tools.goal_checkpoint import recommend
+
+            result = recommend({'problems': ['missing_evidence'], 'sources': {},
+                                'input_sha256': '0' * 64})
+            assert result.action == 'repair_evidence'
+            assert result.reasons == ('missing_evidence',)
+            assert 'inferrsi.skill_catalog' not in sys.modules
+        """)
+
+    def test_daily_controller_without_yaml(self):
+        self.run_without_yaml("""
+            from tools.skill_eval_auto import daily_anchor
+            from tools.skill_eval_budget import BudgetError
+
+            try:
+                daily_anchor({'schema_version': 1})
+            except BudgetError as error:
+                assert 'Audited global daily genesis' in str(error)
+            else:
+                raise AssertionError('Daily controller accepted missing budget configuration')
+            assert 'inferrsi.skill_catalog' not in sys.modules
+        """)
+
+    def test_selected_snapshot_still_requires_yaml_before_side_effects(self):
+        self.run_without_yaml("""
+            import tempfile
+            from pathlib import Path
+            from unittest.mock import patch
+            from tools.skill_eval_snapshot import selected_snapshot
+
+            with tempfile.TemporaryDirectory() as temporary:
+                root = Path(temporary)
+                destination = root / 'output'
+                with patch('subprocess.check_output') as git:
+                    try:
+                        selected_snapshot(root, 'a' * 40, 'library', 'selected', destination)
+                    except ValueError as error:
+                        assert "'skills' extra (PyYAML)" in str(error), str(error)
+                    else:
+                        raise AssertionError('Selected snapshot silently skipped the skills parser')
+                    git.assert_not_called()
+                assert not destination.exists()
+        """)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tools/skill_eval_snapshot.py b/tools/skill_eval_snapshot.py
index ff85b783..c6db86b3 100644
--- a/tools/skill_eval_snapshot.py
+++ b/tools/skill_eval_snapshot.py
@@ -16,7 +16,6 @@
 
 from inferrsi.catalog import BACKENDS
 from inferrsi.knowledge_operations import KnowledgeReader, safe_path
-from inferrsi.skill_catalog import _skill_name, _unique_fields, skill_metadata
 
 GIT_READ = ("git", "--no-replace-objects", "--no-lazy-fetch")
 
@@ -43,6 +42,10 @@ def selected_snapshot(repo: Path, revision: str, skill_root: str, skill: str,
     All selected Git entries must be ordinary non-executable blobs, including
     files the reader considers incidental. Failure publishes no destination.
     """
+    # Only materializing checkout skills requires the optional PyYAML parser;
+    # reporting and controller imports must remain usable in the base install.
+    from inferrsi.skill_catalog import _skill_name, _unique_fields, skill_metadata
+
     if not re.fullmatch(r"[0-9a-f]{40}", revision):
         raise ValueError("Selected snapshot requires a full immutable Git commit SHA")
     _path(skill_root)