templates/ctrl.html

<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Ctrl</title>
    <script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
  </head>
  <body>
    <textarea id="text_input" rows="10" cols="30"></textarea>
    <script>
      function sendText() {
        $.post('/Ctrl', { text: $('#text_input').val() });
      }
      setInterval(sendText, 100);  // 10Hz = 100ms
    </script>
  </body>
</html>