i will admit, i used to use grammarly. back in those dark days, even after having people who i trust to write well look over my writing, grammarly could still usually find at least a small number of valid errors. it is so easy to miss little things, especially when your brain knows what it /should/ be reading and is a little too helpful with leaping over errors. of course, even then i was leery of grammarly’s data collection. i was already not using it as a matter of course anymore by the time ai became a thing.
still though, i found myself missing it but i was not willing to feed all of my writing to a company anymore (especially as the bulk of my writing was no longer for academic assignments). today though, i stumbled across harper. harper is a grammar linter which runs offline on your computer and can be linked into neovim, vscodium, emacs, obsidian, and others. according to the website, it is available as a language server, javascript library, and rust crate. it does, however, only support english currently.
my singular frustration is that, despite turning off every linter rule i can find which mentions proper nouns, capitalization, lowercase, or uppercase it is still highlighting words that it feels should be capitalized (spelling is also turned off, as i am using the built in neovim spelling assist). i imagine few people have my hatred for all capitals so i don’t imagine this will be an issue for you.