diff --git a/app/webui/404.html b/app/webui/404.html
new file mode 100644
index 0000000..77e9539
--- /dev/null
+++ b/app/webui/404.html
@@ -0,0 +1,29 @@
+<!doctype html>
+<html lang="de">
+<head>
+    <meta charset="utf-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <title>404 – Seite nicht gefunden</title>
+
+    <script src="https://cdn.tailwindcss.com"></script>
+    <link rel="stylesheet" href="/css/app.css" />
+    <script defer src="https://cdn.jsdelivr.net/npm/alpinejs@3.14.1/dist/cdn.min.js"></script>
+</head>
+<body class="min-h-screen flex items-center justify-center bg-slate-50 p-4">
+
+    <div class="crm-card text-center max-w-md" x-data="{}">
+        <h1 class="text-6xl font-bold text-slate-900 mb-2">404</h1>
+        <p class="text-xl text-slate-700 mb-2">Seite nicht gefunden</p>
+        <p class="text-sm text-slate-500 mb-6">
+            Die angeforderte URL existiert nicht oder du bist nicht berechtigt.
+        </p>
+        <a href="/dashboard.html" class="btn-primary inline-block mb-2">Zum Dashboard</a>
+        <a href="/app.html" class="btn-secondary inline-block">Oder zur App-Startseite</a>
+
+        <p class="text-xs text-slate-400 mt-6">
+            Falls du eine bestimmte Page suchst: Accounts, Contacts, Pipeline oder Activities.
+        </p>
+    </div>
+
+</body>
+</html>
