diff --git a/app.js b/app.js
index 6e85528..932932e 100644
--- a/app.js
+++ b/app.js
@@ -126,11 +126,44 @@ window.addEventListener('resize', () => {
   renderer.setSize(window.innerWidth, window.innerHeight);
 });
 
+// === PERFORMANCE MONITOR ===
+const PERF = {
+  frameTimeLimit: 33, // ms — ~30fps minimum
+  slowFrameThreshold: 5, // consecutive slow frames before alerting
+  slowFrameCount: 0,
+  lastTime: performance.now(),
+  warned: false,
+};
+
+const perfWarning = document.getElementById('perf-warning');
+
+function checkFrameTime(now) {
+  const frameTime = now - PERF.lastTime;
+  PERF.lastTime = now;
+
+  if (frameTime > PERF.frameTimeLimit) {
+    PERF.slowFrameCount++;
+    if (PERF.slowFrameCount >= PERF.slowFrameThreshold && !PERF.warned) {
+      PERF.warned = true;
+      console.warn(`[Nexus] Performance regression: frame time ${frameTime.toFixed(1)}ms exceeds ${PERF.frameTimeLimit}ms limit`);
+      if (perfWarning) perfWarning.hidden = false;
+    }
+  } else {
+    PERF.slowFrameCount = 0;
+    if (PERF.warned) {
+      PERF.warned = false;
+      if (perfWarning) perfWarning.hidden = true;
+    }
+  }
+}
+
 // === ANIMATION LOOP ===
 const clock = new THREE.Clock();
 
 function animate() {
   requestAnimationFrame(animate);
+  const now = performance.now();
+  checkFrameTime(now);
   const elapsed = clock.getElapsedTime();
 
   // Slow auto-rotation
diff --git a/index.html b/index.html
index 2006413..70ea233 100644
--- a/index.html
+++ b/index.html
@@ -36,6 +36,8 @@
     <audio id="ambient-sound" src="ambient.mp3" loop></audio>
   </div>
 
+  <div id="perf-warning" hidden>SLOW FRAME</div>
+
   <script type="module" src="app.js"></script>
 </body>
 </html>
diff --git a/style.css b/style.css
index 948c916..17a4277 100644
--- a/style.css
+++ b/style.css
@@ -56,6 +56,23 @@ canvas {
   background-color: var(--color-text-muted);
 }
 
+/* === PERFORMANCE WARNING === */
+#perf-warning {
+  position: fixed;
+  bottom: 12px;
+  left: 50%;
+  transform: translateX(-50%);
+  background: rgba(255, 60, 60, 0.85);
+  color: #fff;
+  font-family: var(--font-body);
+  font-size: 11px;
+  letter-spacing: 0.1em;
+  padding: 4px 12px;
+  border-radius: 4px;
+  z-index: 100;
+  pointer-events: none;
+}
+
 /* === DEBUG MODE === */
 #debug-toggle {
   margin-left: 8px;