diff --git a/tests/test_memory_query_router.py b/tests/test_memory_query_router.py
new file mode 100644
index 000000000..4a1b42d47
--- /dev/null
+++ b/tests/test_memory_query_router.py
@@ -0,0 +1,97 @@
+"""
+Tests for hybrid memory query router
+
+Issue: #663
+"""
+
+import unittest
+from tools.memory_query_router import (
+    SearchMethod,
+    QueryRouter,
+    route_query,
+    reciprocal_rank_fusion,
+    merge_with_hrr_priority,
+)
+
+
+class TestQueryClassification(unittest.TestCase):
+    
+    def setUp(self):
+        self.router = QueryRouter()
+    
+    def test_contradiction_routes_hrr(self):
+        c = self.router.classify("What contradicts this statement?")
+        self.assertEqual(c.method, SearchMethod.HRR)
+        self.assertGreater(c.confidence, 0.9)
+    
+    def test_compositional_routes_hrr(self):
+        c = self.router.classify("How does Python relate to machine learning?")
+        self.assertEqual(c.method, SearchMethod.HRR)
+        
+        c = self.router.classify("What is associated with quantum computing?")
+        self.assertEqual(c.method, SearchMethod.HRR)
+    
+    def test_exact_keywords_routes_fts5(self):
+        c = self.router.classify('Find documents containing "FastAPI tutorial"')
+        self.assertEqual(c.method, SearchMethod.FTS5)
+    
+    def test_short_query_routes_fts5(self):
+        c = self.router.classify("Python syntax")
+        self.assertEqual(c.method, SearchMethod.FTS5)
+    
+    def test_temporal_routes_fts5(self):
+        c = self.router.classify("Recent changes to the config")
+        self.assertEqual(c.method, SearchMethod.FTS5)
+    
+    def test_semantic_routes_vector(self):
+        c = self.router.classify("Explain how transformers work in natural language processing")
+        self.assertEqual(c.method, SearchMethod.VECTOR)
+
+
+class TestReciprocalRankFusion(unittest.TestCase):
+    
+    def test_basic_fusion(self):
+        results = {
+            "hrr": [("a", 0.9), ("b", 0.8)],
+            "vector": [("b", 0.85), ("c", 0.7)],
+        }
+        merged = reciprocal_rank_fusion(results)
+        
+        # 'b' appears in both, should rank high
+        ids = [r[0] for r in merged]
+        self.assertIn("b", ids[:2])
+    
+    def test_empty_results(self):
+        merged = reciprocal_rank_fusion({})
+        self.assertEqual(len(merged), 0)
+
+
+class TestHRRPriority(unittest.TestCase):
+    
+    def test_compositional_hrr_first(self):
+        hrr = [("a", 0.9), ("b", 0.8)]
+        vector = [("c", 0.85), ("d", 0.7)]
+        fts5 = [("e", 0.6)]
+        
+        merged = merge_with_hrr_priority(hrr, vector, fts5, "compositional")
+        
+        # HRR results should come first
+        self.assertEqual(merged[0][0], "a")
+        self.assertEqual(merged[1][0], "b")
+
+
+class TestHybridDecision(unittest.TestCase):
+    
+    def test_low_confidence_uses_hybrid(self):
+        from tools.memory_query_router import should_use_hybrid
+        # Ambiguous query
+        self.assertTrue(should_use_hybrid("Tell me about things"))
+    
+    def test_clear_query_no_hybrid(self):
+        from tools.memory_query_router import should_use_hybrid
+        # Clear contradiction query
+        self.assertFalse(should_use_hybrid("What contradicts X?"))
+
+
+if __name__ == "__main__":
+    unittest.main()