This is magnificent. Proper grammar & spell-checking in #emacs #orgmode with https://github.com/valentjn/ltex-ls.
It takes maybe 10 seconds to run on my Master’s thesis file (M-x count words: 13453 words and 117566 characters), but it’s totally worth it. And it’s much faster on smaller files.
The good thing is that it supports markup syntaxes like Org and Markdown. #languagetool by itself produces a lot of false positives on these files.