diff --git a/index-b.html b/index-b.html
index ec4a95d..c4c803b 100644
--- a/index-b.html
+++ b/index-b.html
@@ -654,5 +654,17 @@
 <script>
 if (window.lucide) lucide.createIcons();
 </script>
+
+<!-- Dev toggle — visible only when ?dev=1 -->
+<script>
+(function(){
+    if(!location.search.includes('dev=1')) return;
+    const btn = document.createElement('a');
+    btn.href = '/?dev=1';
+    btn.textContent = '← Design A';
+    btn.style.cssText = 'position:fixed;bottom:20px;right:20px;z-index:9999;font-family:monospace;font-size:11px;padding:6px 12px;background:rgba(255,255,255,0.9);color:#2D9B6B;border:1px solid #2D9B6B;border-radius:6px;text-decoration:none;box-shadow:0 2px 8px rgba(0,0,0,0.12);';
+    document.body.appendChild(btn);
+})();
+</script>
 </body>
 </html>
diff --git a/index.html b/index.html
index 3fc21b7..a7a0c9f 100644
--- a/index.html
+++ b/index.html
@@ -592,5 +592,17 @@ if ('serviceWorker' in navigator) {
 }
 if (window.lucide) lucide.createIcons();
 </script>
+
+<!-- Dev toggle — visible only when ?dev=1 -->
+<script>
+(function(){
+    if(!location.search.includes('dev=1')) return;
+    const btn = document.createElement('a');
+    btn.href = '/index-b.html?dev=1';
+    btn.textContent = 'Design B →';
+    btn.style.cssText = 'position:fixed;bottom:20px;right:20px;z-index:9999;font-family:monospace;font-size:11px;padding:6px 12px;background:rgba(0,0,0,0.7);color:#6EE7B7;border:1px solid #6EE7B7;border-radius:6px;text-decoration:none;backdrop-filter:blur(8px);';
+    document.body.appendChild(btn);
+})();
+</script>
 </body>
 </html>