The LanguageTool browser add-on uses the account linked to your languagetool.org login. To check with which account you’re logged in in the browser add-on, take the following steps:
Click the LanguageTool icon in your browser toolbar.
Select the gear icon to open the settings menu.
In the "Account" section, you’ll see the email address currently associated with the add-on.
This is the account being used to access your LanguageTool features, including any Premium access.
If you'd like to update the email address linked to your LanguageTool account, you can find instructions here.