Mostly decent, but British English is not listed as a mother tongue or preferred language, so I was constantly get 'corrections' from British English to American.
I CANNOT have English 'no variant' as ONLY option shows US flag for both mother tongue and preferred language. The only place where English British is available is variants which doesn't seem to ever come into play when I was using this as it only ever flagged up British spellings wanting to change them to American.
I'd post screenshots but i cant seem to be able to.

Macht einen sehr guten Eindruck.

Fabulous extension. Works in many situations. Hours of fun. Highly recommended.

Edit: It didn't detect a single grammar mistake in these test sentences:
"Me typing sentences with the worst grammar for demonstration purposes"
"Me like drink banana smoothies"
"Me confused as to why LanguageTool not detecting simple grammar mistake like these"

Très bon correcteur mais il n'identifie pas automatiquement la langue de l'utilisateur ce qui est très énervent car je doit changer a chaque fois langue de correction qu'il ne mémorise pas.

Must have - und ich habe nur wenige Tools instaliert. Das hilft mir beim Texten von Webseiten und Post wirklich weiter. Cool und Danke

классное расширение, очень помогает в работе

Uma mão na roda, sempre me ajuda.

AMO!O CORRETOR TOOL COM ELE MELHOREI MINHA ESCRITA

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)

Ce module a tendance à vous imposer des virgules qui n'ont rien d'indispensable.