diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index fcfca4e..5d62d63 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -1331,6 +1331,11 @@ public sealed class GameWindow : IDisposable
         _capturedMouse = isFlyMode ? mouse : null;
     }
 
+    // Performance overlay state — updated every ~0.5s and written to the
+    // window title so there's zero rendering cost (no font/overlay needed).
+    private double _perfAccum;
+    private int _perfFrameCount;
+
     private void OnRender(double deltaSeconds)
     {
         _gl!.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
@@ -1340,12 +1345,40 @@ public sealed class GameWindow : IDisposable
         if (_animatedEntities.Count > 0)
             TickAnimations((float)deltaSeconds);
 
+        int visibleLandblocks = 0;
+        int totalLandblocks = 0;
+
         if (_cameraController is not null)
         {
             var camera = _cameraController.Active;
             var frustum = AcDream.App.Rendering.FrustumPlanes.FromViewProjection(camera.View * camera.Projection);
             _terrain?.Draw(camera, frustum);
             _staticMesh?.Draw(camera, _worldState.LandblockEntries, frustum);
+
+            // Count visible vs total for the perf overlay.
+            foreach (var entry in _worldState.LandblockEntries)
+            {
+                totalLandblocks++;
+                if (AcDream.App.Rendering.FrustumCuller.IsAabbVisible(frustum, entry.AabbMin, entry.AabbMax))
+                    visibleLandblocks++;
+            }
+        }
+
+        // Update the window title with performance stats every ~0.5s.
+        _perfAccum += deltaSeconds;
+        _perfFrameCount++;
+        if (_perfAccum >= 0.5)
+        {
+            double avgFrameTime = _perfAccum / _perfFrameCount * 1000.0;
+            double fps = _perfFrameCount / _perfAccum;
+            int entityCount = _worldState.Entities.Count;
+            int animatedCount = _animatedEntities.Count;
+
+            _window!.Title = $"acdream | {fps:F0} fps | {avgFrameTime:F1} ms | " +
+                             $"lb {visibleLandblocks}/{totalLandblocks} visible | " +
+                             $"ent {entityCount} | anim {animatedCount}";
+            _perfAccum = 0;
+            _perfFrameCount = 0;
         }
     }