If you aren't ready to pay for Grammarly, this is your grammar checker of choice. Free versions of these two services are more or less similar, and both are good

However, the premium version of Grammarly is just better. Outrageously expensive and English-only -- yes. But in terms of convenience, accuracy, and usefulness, LanguageTool is not on the same level (yet?), unfortunately

(I use LanguageTool, by the way)