Harper: open-source grammar checker that runs fully locally with sub-10ms suggestions
thisguyknowsai · x · 2026-11-10
Harper is a free, open-source grammar checker positioned as a privacy-respecting Grammarly alternative. Every check runs locally — no cloud round-trips, no telemetry, no LLM in the loop — with suggestions returned in under 10ms, so your writing never leaves your device.
It catches grammar and spelling mistakes, awkward phrasing, and capitalization errors. Integrations include Chrome/Firefox/Edge extensions, a native macOS desktop app (system-wide for every text field), VS Code, Obsidian, Neovim, Zed and WordPress, plus a JavaScript library and language server for developers, with custom dictionaries and grammar rules. English only for now; it's built for grammar checking, not AI rewriting.
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