Great! If you don't like sending your data to a third party network you can use this add on with a locally hosted instance on your computer or on a private network.

I simply run language tool from the command line like this:

languagetool --http --allow-origin "*"
default port is 8081 but you can specify another one by adding this : --port 666

then in the add on preferences simply change the LanguageTool API Server URL to:
http://localhost:8081/v2/