diff --git a/tests/test_config_drift.py b/tests/test_config_drift.py
new file mode 100644
index 00000000..265dd78b
--- /dev/null
+++ b/tests/test_config_drift.py
@@ -0,0 +1,149 @@
+"""
+Tests for scripts/config_drift.py — Config drift detection.
+"""
+
+import json
+import tempfile
+import unittest
+from pathlib import Path
+
+import sys
+sys.path.insert(0, str(Path(__file__).parent.parent / "scripts"))
+from config_drift import (
+    get_nested_value,
+    compare_configs,
+    parse_yaml_basic,
+    generate_report,
+)
+
+
+class TestGetNestedValue(unittest.TestCase):
+    def test_top_level(self):
+        config = {"provider": "openrouter"}
+        self.assertEqual(get_nested_value(config, "provider"), "openrouter")
+
+    def test_nested(self):
+        config = {"cron": {"enabled": True, "workers": 4}}
+        self.assertEqual(get_nested_value(config, "cron.enabled"), True)
+        self.assertEqual(get_nested_value(config, "cron.workers"), 4)
+
+    def test_missing_key(self):
+        config = {"provider": "openrouter"}
+        self.assertIsNone(get_nested_value(config, "missing"))
+
+    def test_missing_nested(self):
+        config = {"cron": {}}
+        self.assertIsNone(get_nested_value(config, "cron.enabled"))
+
+    def test_deep_nesting(self):
+        config = {"a": {"b": {"c": "value"}}}
+        self.assertEqual(get_nested_value(config, "a.b.c"), "value")
+
+
+class TestCompareConfigs(unittest.TestCase):
+    def test_no_diff(self):
+        canonical = {"provider": "openrouter", "model": "mimo"}
+        remote = {"provider": "openrouter", "model": "mimo"}
+        diffs = compare_configs(canonical, remote, ["provider", "model"])
+        self.assertEqual(diffs, [])
+
+    def test_single_diff(self):
+        canonical = {"provider": "openrouter"}
+        remote = {"provider": "anthropic"}
+        diffs = compare_configs(canonical, remote, ["provider"])
+        self.assertEqual(len(diffs), 1)
+        self.assertEqual(diffs[0][0], "provider")
+        self.assertEqual(diffs[0][1], "openrouter")
+        self.assertEqual(diffs[0][2], "anthropic")
+
+    def test_multiple_diffs(self):
+        canonical = {"provider": "openrouter", "model": "mimo"}
+        remote = {"provider": "anthropic", "model": "claude"}
+        diffs = compare_configs(canonical, remote, ["provider", "model"])
+        self.assertEqual(len(diffs), 2)
+
+    def test_nested_diff(self):
+        canonical = {"cron": {"enabled": True}}
+        remote = {"cron": {"enabled": False}}
+        diffs = compare_configs(canonical, remote, ["cron.enabled"])
+        self.assertEqual(len(diffs), 1)
+        self.assertEqual(diffs[0][0], "cron.enabled")
+
+    def test_missing_in_remote(self):
+        canonical = {"provider": "openrouter"}
+        remote = {}
+        diffs = compare_configs(canonical, remote, ["provider"])
+        self.assertEqual(len(diffs), 1)
+
+    def test_extra_in_remote(self):
+        canonical = {}
+        remote = {"provider": "openrouter"}
+        diffs = compare_configs(canonical, remote, ["provider"])
+        self.assertEqual(len(diffs), 1)
+
+
+class TestParseYamlBasic(unittest.TestCase):
+    def test_simple(self):
+        content = "provider: openrouter\nmodel: mimo-v2-pro\n"
+        result = parse_yaml_basic(content)
+        self.assertEqual(result["provider"], "openrouter")
+        self.assertEqual(result["model"], "mimo-v2-pro")
+
+    def test_boolean(self):
+        content = "enabled: true\ndisabled: false\n"
+        result = parse_yaml_basic(content)
+        self.assertEqual(result["enabled"], True)
+        self.assertEqual(result["disabled"], False)
+
+    def test_integer(self):
+        content = "workers: 4\nport: 8080\n"
+        result = parse_yaml_basic(content)
+        self.assertEqual(result["workers"], 4)
+        self.assertEqual(result["port"], 8080)
+
+    def test_comments_skipped(self):
+        content = "# This is a comment\nprovider: openrouter\n"
+        result = parse_yaml_basic(content)
+        self.assertNotIn("#", result)
+        self.assertEqual(result["provider"], "openrouter")
+
+    def test_quoted_values(self):
+        content = 'name: "hello world"\nother: \'single quotes\'\n'
+        result = parse_yaml_basic(content)
+        self.assertEqual(result["name"], "hello world")
+        self.assertEqual(result["other"], "single quotes")
+
+
+class TestGenerateReport(unittest.TestCase):
+    def test_all_ok(self):
+        results = {
+            "node1": {"status": "ok", "diffs": []},
+            "node2": {"status": "ok", "diffs": []},
+        }
+        report = generate_report(results, ["provider"])
+        self.assertIn("OK", report)
+        self.assertIn("2 ok", report)
+
+    def test_drift_reported(self):
+        results = {
+            "node1": {
+                "status": "drift",
+                "diffs": [("provider", "openrouter", "anthropic")]
+            },
+            "node2": {"status": "ok", "diffs": []},
+        }
+        report = generate_report(results, ["provider"])
+        self.assertIn("DRIFT DETECTED", report)
+        self.assertIn("openrouter", report)
+        self.assertIn("anthropic", report)
+
+    def test_unreachable_reported(self):
+        results = {
+            "node1": {"status": "unreachable", "diffs": []},
+        }
+        report = generate_report(results, ["provider"])
+        self.assertIn("UNREACHABLE", report)
+
+
+if __name__ == "__main__":
+    unittest.main()