I'm attempting to add a checkbox to a field settings form in D9. I have the following code:

function my_module_field_formatter_third_party_settings_form(\Drupal\Core\Field\FormatterInterface $plugin, \Drupal\Core\Field\FieldDefinitionInterface $field_definition, $view_mode, $form, \Drupal\Core\Form\FormStateInterface $form_state) {
  $element = array();
  print '<h1>HERE</h1>';

  if ($plugin
    ->getPluginId() == 'text_textarea_with_summary') {
    $element['my_setting'] = array(
      '#type' => 'checkbox',
      '#title' => t('test'),
      '#default_value' => $plugin
        ->getThirdPartySetting('my_module', 'my_setting'),
  return $element;

I then edit an instance of a body field (admin/structure/types/manage/article/fields/node.article.body), and the hook doesn't fire...no debug text nor stopping at the breakpoint on that same line.

  • Hopefully a silly question, but did you clear the cache after writing the hook function?
    – Clive
    Oct 21, 2020 at 18:41
  • Yup. And I also have hook_field_widget_form_alter and it breaks at a breakpoint, so it’s not the module file or the xdebug setup.
    – JAyenGreen
    Oct 21, 2020 at 18:44

1 Answer 1


There are two problems.

/admin/structure/types/manage/article/fields/node.article.body is the path of a field setting. To trigger the hook you need to visit /admin/structure/types/manage/article/display.

The plugin ID is wrong, too. text_textarea_with_summary is the plugin ID of a widget. What you are looking for is probably the formatter text_summary_or_trimmed.

If this is neither formatter nor widget, but the content type specific field definition, then use a normal form alter hook, because there is no specific hook to add third party settings:

use Drupal\Core\Form\FormStateInterface;

 * Implements hook_form_FORM_ID_form_alter().
function my_module_form_field_config_edit_form_alter(array &$form, FormStateInterface $form_state) {
  /** @var \Drupal\Core\Field\FieldConfigInterface $field */
  $field = $form_state->getFormObject()->getEntity();
  if ($field->getType() == 'text_with_summary') {
    $form['third_party_settings']['my_module']['my_setting'] = [
      '#type' => 'checkbox',
      '#title' => t('test'),
      '#default_value' => $field->getThirdPartySetting('my_module', 'my_setting'),

Edit: The form keys $form['third_party_settings']['my_module']['my_setting'] are important. They are used to submit the third party settings.

  • So with adding to the form settings form being the goal, I’m barking up the wrong tree?
    – JAyenGreen
    Oct 22, 2020 at 12:37
  • This depends on whether the field settings should be stored for a field instance in general, specific for a content type or more specific for a view/form mode. Your question somehow makes all of this possible.
    – 4uk4
    Oct 22, 2020 at 12:58
  • It would be for a field instance, to give the user adding the field instance an option in addition to Required, etc. I was under the impression that doing so from a custom module was a third-party setting.
    – JAyenGreen
    Oct 22, 2020 at 13:17
  • OK, then use a form alter hook. See the edited answer.
    – 4uk4
    Oct 22, 2020 at 13:48
  • Thank you, once again!
    – JAyenGreen
    Oct 22, 2020 at 14:17

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