diff --git a/test_record_tool_usage.py b/test_record_tool_usage.py
new file mode 100644
index 00000000..22105c44
--- /dev/null
+++ b/test_record_tool_usage.py
@@ -0,0 +1,93 @@
+import pytest
+import copy
+from unittest.mock import patch, MagicMock
+
+import router.main
+
+# Save the original stats dictionary to reset it after each test
+_ORIGINAL_STATS = copy.deepcopy(router.main.stats)
+
+@pytest.fixture(autouse=True)
+def reset_stats(monkeypatch):
+    """Fixture to reset the stats dictionary before each test to ensure isolation."""
+    # We patch the stats dict with a fresh copy of the original
+    monkeypatch.setattr(router.main, "stats", copy.deepcopy(_ORIGINAL_STATS))
+    yield
+
+@pytest.fixture(autouse=True)
+def mock_persistence():
+    """Mock out disk writing functions to avoid side effects during tests."""
+    with patch("router.main._atomic_write_json_sync"), patch("router.main.save_persisted_stats"):
+        yield
+
+def test_record_tool_usage_basic():
+    """Test basic token recording for a standard tool."""
+    router.main.record_tool_usage(
+        tool_name="shell",
+        prompt_tokens=10,
+        completion_tokens=20,
+        model="gpt-4",
+        latency_ms=150.0
+    )
+
+    assert router.main.stats["tool_tokens"]["shell"] == 30
+    assert router.main.stats["prompt_tokens"] == 10
+    assert router.main.stats["completion_tokens"] == 20
+    assert router.main.stats["routing_paths"]["litellm_fallback"] == 1
+
+    assert len(router.main.stats["timeline"]) == 1
+    event = router.main.stats["timeline"][0]
+    assert event["tool"] == "shell"
+    assert event["model"] == "gpt-4"
+    assert event["route"] == "litellm_fallback"
+    assert event["tokens"] == 30
+    assert event["latency_ms"] == 150
+
+def test_record_tool_usage_none_mapping():
+    """Test that 'none' tool is correctly mapped to 'other'."""
+    router.main.record_tool_usage(
+        tool_name="none",
+        prompt_tokens=5,
+        completion_tokens=5,
+        model="gpt-4",
+        latency_ms=100.0
+    )
+
+    assert "none" not in router.main.stats["tool_tokens"] or router.main.stats["tool_tokens"].get("none") == 0
+    assert router.main.stats["tool_tokens"]["other"] == 10
+
+def test_record_tool_usage_accumulation():
+    """Test that tokens accumulate correctly over multiple calls."""
+    router.main.record_tool_usage("write", 10, 10, "model1", 50.0)
+    router.main.record_tool_usage("write", 20, 30, "model2", 60.0)
+
+    assert router.main.stats["tool_tokens"]["write"] == 70
+    assert router.main.stats["prompt_tokens"] == 30
+    assert router.main.stats["completion_tokens"] == 40
+    assert len(router.main.stats["timeline"]) == 2
+
+def test_record_tool_usage_timeline_limit():
+    """Test that the timeline buffer is capped at 15 events."""
+    # Add 20 events
+    for i in range(20):
+        router.main.record_tool_usage(f"tool_{i}", 1, 1, "model", 10.0)
+
+    assert len(router.main.stats["timeline"]) == 15
+    # The first 5 events should be popped off, so the oldest event in the timeline
+    # should be from tool_5 (since we started at tool_0).
+    assert router.main.stats["timeline"][0]["tool"] == "tool_5"
+    assert router.main.stats["timeline"][-1]["tool"] == "tool_19"
+
+def test_record_tool_usage_custom_route():
+    """Test recording tool usage with a custom route."""
+    router.main.record_tool_usage(
+        tool_name="tree",
+        prompt_tokens=5,
+        completion_tokens=5,
+        model="gpt-4",
+        latency_ms=100.0,
+        route="google_oauth_direct"
+    )
+
+    assert router.main.stats["routing_paths"]["google_oauth_direct"] == 1
+    assert router.main.stats["routing_paths"]["litellm_fallback"] == 0