CSpell is the thing everyone uses in VSCode, but they don't offer an LSP for other editors to use. Someone has made an LSP for it, but CSpell is also pretty slow since it's all in JavaScript. After spending way too much time[0] trying to find an alternative, I just wrote my own.
Codebook[1] is written in Rust, so it's very fast, and (IMO) is much less annoying than CSpell because it uses Tree Sitter to only find spelling issues that the developer has control over.
Codebook also comes with an LSP, so it could be used in other editors, but I haven't tried that yet.
I want to also shout out to Spellbook[2], which is the actual spell checking engine I used to make Codebook. The makers of Helix wrote it, and it's fantastic.
[0]: https://blopker.com/writing/09-survey-of-the-current-state-o... [1]: https://github.com/blopker/codebook [2]: https://github.com/helix-editor/spellbook
