diff --git a/today/book/index.html b/today/book/index.html
index 46e9e12..acce773 100644
--- a/today/book/index.html
+++ b/today/book/index.html
@@ -39,6 +39,13 @@
         </script>
         <!-- Start loading toc.js asap -->
         <script src="toc.js"></script>
+        <script type="text/javascript">
+            (function(c,l,a,r,i,t,y){
+                c[a]=c[a]||function(){(c[a].q=c[a].q||[]).push(arguments)};
+                t=l.createElement(r);t.async=1;t.src="https://www.clarity.ms/tag/"+i;
+                y=l.getElementsByTagName(r)[0];y.parentNode.insertBefore(t,y);
+            })(window, document, "clarity", "script", "s0drt9kmxf");
+        </script>
     </head>
     <body>
     <div id="mdbook-help-container">
