How can to make required the fields keywords and description of the metatags module?
You can use code similar to the following in a custom module/theme:

function MYMODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if (isset($form['metatags'])) {
    if (isset($form['metatags']['description']['value'])) {
      $form['metatags']['description']['value']['#required'] = TRUE;
    }
    if (isset($form['metatags']['keywords']['value'])) {
      $form['metatags']['keywords']['value']['#required'] = TRUE;
    }
  }
}