I am trying to integrate a custom CKEditor 5 plugin (LanguageTool) into Drupal 10 using a custom module. The plugin builds successfully, but when Drupal loads the editor, the browser console shows:

CKEditorError: plugincollection-plugin-not-found {"plugin": null}

The editor loads, but the custom plugin does not initialize.

🟩 What I Have Done (Summary)

• Created a CKEditor 5 custom build with the plugin included.

• Ran npm install and npm run build.

• Copied the generated build/ckeditor.js into my Drupal custom module.

• Created a Drupal CKEditor5 plugin class:

/**
 * @CKEditor5Plugin(
 *   id = "ckeditor5_languagetool_plugin",
 *   label = @Translation("LanguageTool")
 * )
 */
class LanguageTool extends CKEditor5PluginBase {
  public function getPlugins() {
    return [ 'LanguageTool' ]; // JS pluginName
  }
}

• Added library in my_module.libraries.yml

• Enabled plugin in text format

• Cleared caches (drush cr)

🟥 Current Problem

The error indicates that Drupal is requesting a CKEditor plugin with name "null", which usually means:

• Plugin ID mismatch

• Plugin name in text format config does not match PHP annotation

• JS pluginName does not match getPlugins() return value

But after checking, I still see the error.

🟦 Code / Config Samples

PHP plugin class

/**
 * @CKEditor5Plugin(
 *   id = "ckeditor5_languagetool_plugin"
 * )
 */
class LanguageTool extends CKEditor5PluginBase {
  public function getPlugins() {
    return [ 'LanguageTool' ];
  }
}

JS plugin

export default class LanguageTool extends Plugin {
  static get pluginName() {
    return 'LanguageTool';
  }
}

Text format config

ckeditor5.plugin.ckeditor5_languagetool_plugin:
  enabled: true

🟧 What I Want to Know

1. Should the Drupal plugin ID (ckeditor5_languagetool_plugin) match directly with the JS pluginName or only with the text format entry?

2. Are there any known issues about custom plugin loading with Drupal CKEditor 5 integration?

3. Is there a debugging method to see which plugin name Drupal is sending to CKEditor?

4. Am I missing any step in mapping the Drupal plugin to CKEditor’s pluginName?

🟩 Environment

• Drupal 10.x

• CKEditor 5 custom build

• Custom Drupal module

• PHP 8.1

• Browser: Chrome