diff --git a/public/index.html b/public/index.html
index 37c8f73..734948c 100644
--- a/public/index.html
+++ b/public/index.html
@@ -92,6 +92,9 @@
   <span id="trk">—</span>
   <span id="cnt">—</span>
 </div>
+<pre id="dbg" style="position:fixed;top:8px;left:8px;margin:0;padding:6px 8px;z-index:9998;
+  background:rgba(6,8,15,.72);color:#8fffd0;font:11px/1.45 monospace;border-radius:6px;
+  pointer-events:none;white-space:pre;display:none"></pre>
 <button id="shutter" class="hidden" aria-label="Take photo"></button>
 <div id="flash"></div>
 <div id="toast"></div>