CKEditorError: plugincollection-plugin-not-found {"plugin": null} when integrating custom CKEditor5 plugin with Drupal 10

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.

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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)

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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.

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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

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

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

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

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

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Drupal 10.x

CKEditor 5 custom build

Custom Drupal module

PHP 8.1

Browser: Chrome