I use Harper as my spell checker everywhere. Not because it’s fancy - because it’s fast, not bloated, and open-source. It runs on my machine, checks a note in ~40 milliseconds, and doesn’t send my text anywhere.
It worked in my code editor and my browser. It didn’t work in Joplin - where I write most. So I built the plugin.
Harper for Joplin: spelling and grammar checking inside Joplin’s Markdown editor, on desktop and Android. Underlines as you type (squiggly or solid line - your choice), tap one for suggestions and one-tap fixes. Four English dialects.
Two things I care about most:
- Everything is local. The whole engine ships inside the plugin. No cloud, no account, works offline. That’s why the plugin file is ~21 MB - that’s the entire checker.
- One dictionary everywhere. Words you add are stored in a regular Joplin note, so they sync to all your devices. On desktop it can also mirror to a plain text file - the same file my code editor reads. Add a word on the phone, Zed learns it too.
Built with the help of Claude Code.
Install: Joplin → Tools → Options → Plugins → search Harper. On Android, enable plugin support first (it’s marked Beta). Source: github.com/pmslava/joplin-plugin-harper. The engine is Harper by Automattic - all credit for the checking itself goes there.
What does your spell checker do with your text - and do you know?