Hi, languagetool.org, languagetoolplus.com, and community.languagetool.org might not be available tonight (2018-01-10) from 21:00 to 09:00 CET next morning, due to maintenance work at the hosting company.
The browser add-on should not be affected. If it doesn’t work tonight, make sure the add-on settings point to https://api.languagetool.org/v2 as the LanguageTool server.