diff --git a/marketing/analytics-access.md b/marketing/analytics-access.md
index 834bf24..abcbd73 100644
--- a/marketing/analytics-access.md
+++ b/marketing/analytics-access.md
@@ -27,6 +27,10 @@ one-time setup.
 
 ## GA4 events
 
+Both apps load `gtag.js` only when the page hostname is `rdlabo.dev` or one of its subdomains.
+Local development (`localhost`, `127.0.0.1`) and preview hosts define the `gtag` stub but never
+load the tag, so their page views and clicks do not reach the property.
+
 The site emits these events from article pages:
 
 | Event                  | Meaning                                               |
diff --git a/projects/docs/src/index.html b/projects/docs/src/index.html
index 2e415dd..dcb1fa1 100644
--- a/projects/docs/src/index.html
+++ b/projects/docs/src/index.html
@@ -12,15 +12,20 @@
     <meta name="theme-color" content="#fffaf7" />
     <link rel="icon" type="image/svg+xml" href="/assets/brand/rdlabo-logo.svg" />
     <link rel="apple-touch-icon" href="/assets/brand/apple-touch-icon.png" />
-    <!-- Google tag (gtag.js) -->
-    <script async src="https://www.googletagmanager.com/gtag/js?id=G-EXVGMHNGJG"></script>
+    <!-- Google tag (gtag.js): loaded only on production hosts -->
     <script>
       window.dataLayer = window.dataLayer || [];
       function gtag() {
         dataLayer.push(arguments);
       }
-      gtag('js', new Date());
-      gtag('config', 'G-EXVGMHNGJG', { send_page_view: false });
+      if (/(^|\.)rdlabo\.dev$/.test(window.location.hostname)) {
+        var gtagScript = document.createElement('script');
+        gtagScript.async = true;
+        gtagScript.src = 'https://www.googletagmanager.com/gtag/js?id=G-EXVGMHNGJG';
+        document.head.appendChild(gtagScript);
+        gtag('js', new Date());
+        gtag('config', 'G-EXVGMHNGJG', { send_page_view: false });
+      }
     </script>
   </head>
   <body>
diff --git a/projects/web-site/src/index.html b/projects/web-site/src/index.html
index f01d780..c1c3462 100644
--- a/projects/web-site/src/index.html
+++ b/projects/web-site/src/index.html
@@ -18,15 +18,20 @@
     <link rel="icon" type="image/png" href="/assets/brand/apple-touch-icon.png" />
     <link rel="icon" type="image/svg+xml" href="/assets/brand/rdlabo-logo.svg" />
     <link rel="apple-touch-icon" href="/assets/brand/apple-touch-icon.png" />
-    <!-- Google tag (gtag.js) -->
-    <script async src="https://www.googletagmanager.com/gtag/js?id=G-EXVGMHNGJG"></script>
+    <!-- Google tag (gtag.js): loaded only on production hosts -->
     <script>
       window.dataLayer = window.dataLayer || [];
       function gtag() {
         dataLayer.push(arguments);
       }
-      gtag('js', new Date());
-      gtag('config', 'G-EXVGMHNGJG', { send_page_view: false });
+      if (/(^|\.)rdlabo\.dev$/.test(window.location.hostname)) {
+        var gtagScript = document.createElement('script');
+        gtagScript.async = true;
+        gtagScript.src = 'https://www.googletagmanager.com/gtag/js?id=G-EXVGMHNGJG';
+        document.head.appendChild(gtagScript);
+        gtag('js', new Date());
+        gtag('config', 'G-EXVGMHNGJG', { send_page_view: false });
+      }
     </script>
   </head>
   <body>
