Private Grammar Checker - Harper
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The private grammar checker for 21st Century English
The private grammar checker for 21st Century English
Meet Harper, the grammar-savvy sidekick that never snitches on your prose. I built Harper because I was sick of the false choice between data-hungry cloud tools and sloth-like offline checkers. Harper threads the needle—fast, lightweight, utterly private—so you can polish every clause without surrendering a single keystroke.
• Instant insight, zero latency: suggestions surface the moment you type, no spinners, no lag
• Stone-cold privacy: Harper lives entirely in your browser; your words never leave your machine
• Fluent in four dialects: American 🇺🇸, British 🇬🇧, Canadian 🇨🇦, and Australian 🇦🇺 English
• Markdown-friendly and developer-approved: flags slip-ups in READMEs, code comments, and docs without mangling syntax
• Clutter-free experience: no pop-ups, no subscription nags, no “premium” ransom notes—just quiet competence
• Open source, Rust-powered: inspect the code, fork it, or tweak it to match your workflow
• Ideal for writers who crave precision without paying a privacy tax
• Perfect for developers curating crystal-clear technical documentation
• A haven for minimalists who’d rather write than swat away ads
• Salvation for anyone fed up with bloated grammar behemoths
Install the extension and keep writing—Harper parses each sentence locally, flags awkward phrasing and rogue typos, then slips back into the shadows. No cloud pings, no data lakes—just you and your words, refined.
Latest reviews
- Phoenix
- Unusable. Nearly 100% false-positive rate, with no apparent way to tell it "Stop trying to apply this rule; it is broken". Any time you actually use it to make a change, it doesn't register it correctly, so you can't ctrl-z undo it (this is basic functionality that should be the absolute bare-minimum, and it can't manage that). Also, it's called "Harper" everywhere, except on the list of extensions, where it's nowhere near the "H", because for unknowable reasons the extension itself is PREFIXED with "Private Grammar Checker", as if THAT were its name. tl;dr: Offers no benefits and only wastes time. AVOID.
- Zhizhong
- Amazing open-source spell checker with many customization options