Self-hosted LanguageTool server[0] with browser addon. 18 gigabytes of n-gram data plus machine learning models. You can catch tpyos on 64K of RAM, but not any deep grammar mistakes, un-idiomatic phrases, or mistakes in common proper names.
Sounds like a lot of heavy lifting for something that is maybe slightly better than spell checking 25 years ago.
consider harper instead. I'm using it right now and it highlighted first two words of this comment. https://writewithharper.com/
Grammatik ran in 64K of RAM on a Z80 running CP/M. (The binary included a Forth interpreter so there was a lot of straight up code compaction.) So yeah, you could catch a lot of common English-language infelicities in a startlingly resource constrained environment... in 1983. Certainly a lot more than typos.
(The reason I remember this bright and shiny data point is I spent a week or three reverse engineering it and getting access to the inner interpreter; the office staff actually used it, though.)