diff --git a/.ai/mcp/mcp.json b/.ai/mcp/mcp.json
new file mode 100644
index 0000000..e69de29
diff --git a/content/register.php b/content/register.php
index 78df41d..37d75ee 100644
--- a/content/register.php
+++ b/content/register.php
@@ -4,6 +4,8 @@ require_once "includes/UserDAO.php";
 
 $dao = new UserDAO();
 
+$error = null;
+
 /*
     Verarbeitung des Registrierungs-Formulars
     Funktion: Erstellt neuen Benutzer (Dummy) und speichert ihn im DAO + Session
@@ -15,16 +17,22 @@ if ($_SERVER["REQUEST_METHOD"] === "POST") {
     $nachname = $_POST["nachname"];
     $password = $_POST["password"];
 
-    // Benutzer im DAO speichern (Dummy-Daten)
-    $dao->addUser($email, $vorname . " " . $nachname, $password);
+    // Prüfen, ob die E-Mail bereits registriert ist
+    if ($dao->findUser($email)) {
+        $error = "Diese E-Mail-Adresse ist bereits registriert.";
+    } else {
 
-    // Session setzen = User ist eingeloggt
-    $_SESSION["user"] = $vorname . " " . $nachname;
-    $_SESSION["user_email"] = $email;
+        // Benutzer im DAO speichern (JSON-Dummy-Daten)
+        $dao->addUser($email, $vorname . " " . $nachname, $password);
 
-    // Weiterleitung zum Profil
-    header("Location: index.php?pfad=profile");
-    exit();
+        // Session setzen = User ist eingeloggt
+        $_SESSION["user"] = $vorname . " " . $nachname;
+        $_SESSION["user_email"] = $email;
+
+        // Weiterleitung zum Profil
+        header("Location: index.php?pfad=profile");
+        exit();
+    }
 }
 ?>
 
@@ -37,6 +45,11 @@ if ($_SERVER["REQUEST_METHOD"] === "POST") {
 
         <h1>Jetzt Registrieren!</h1>
 
+        <!-- Fehlermeldung anzeigen -->
+        <?php if ($error): ?>
+            <p style="color:red;"><?php echo $error; ?></p>
+        <?php endif; ?>
+
         <form method="post" action="index.php?pfad=register">
 
             <p class="input-label">Email:</p>
diff --git a/data/users.json b/data/users.json
new file mode 100644
index 0000000..fc1d1a9
--- /dev/null
+++ b/data/users.json
@@ -0,0 +1,7 @@
+[
+  {
+    "email": "test@test.de",
+    "username": "test",
+    "password": "1234"
+  }
+]
\ No newline at end of file
diff --git a/includes/UserDAO.php b/includes/UserDAO.php
index 40e6412..a0d60ce 100644
--- a/includes/UserDAO.php
+++ b/includes/UserDAO.php
@@ -2,39 +2,62 @@
 
 class UserDAO {
 
-    private static array $users = [
-        [
-            "email" => "test@test.de",
-            "username" => "test",
-            "password" => "1234"
-        ]
-    ];
+    private string $file = "data/users.json";
+
+    private function loadUsers() {
+        if (!file_exists($this->file)) {
+            return [];
+        }
+
+        $json = file_get_contents($this->file);
+        $users = json_decode($json, true);
+
+        return is_array($users) ? $users : [];
+    }
+
+    private function saveUsers($users) {
+        file_put_contents(
+            $this->file,
+            json_encode($users, JSON_PRETTY_PRINT)
+        );
+    }
 
     public function findUser($email) {
-        foreach (self::$users as $user) {
+        $users = $this->loadUsers();
+
+        foreach ($users as $user) {
             if ($user["email"] === $email) {
                 return $user;
             }
         }
+
         return null;
     }
 
     public function addUser($email, $username, $password) {
-        self::$users[] = [
+        $users = $this->loadUsers();
+
+        $users[] = [
             "email" => $email,
             "username" => $username,
             "password" => $password
         ];
+
+        $this->saveUsers($users);
     }
 
     public function deleteUser($email) {
-        foreach (self::$users as $i => $user) {
+        $users = $this->loadUsers();
+
+        foreach ($users as $i => $user) {
             if ($user["email"] === $email) {
-                unset(self::$users[$i]);
-                self::$users = array_values(self::$users);
+                unset($users[$i]);
+                $users = array_values($users);
+                $this->saveUsers($users);
                 return true;
             }
         }
+
         return false;
     }
 }
\ No newline at end of file