# Harper

> Harper is an offline grammar and spell checker for English only (US, UK, Canadian, Australian and Indian English), written in Rust and maintained at Automattic (v2.12.0, October 2026). It ships as Chrome and Firefox extensions, an Obsidian plugin, a language server for VS Code, Neovim, Helix, Emacs and Zed, a CLI and a WebAssembly library. Apache-2.0. Every check runs on your device with no LLM involved, so it does no AI rewriting, tone changes or plagiarism checks, and it does not support other languages yet.

- Repository: https://github.com/Automattic/harper
- Official docs: https://writewithharper.com/docs/integrations/language-server
- Checked: 2026-10-15

## What it replaces
- Grammarly: Grammar and spelling checks, Works in the browser and other apps (partial). English grammar and spelling in the browser and editors, fully offline; no AI rewrite, tone or plagiarism check.

## Facts, with sources

| Question | Status | Answer | Source | Checked |
|---|---|---|---|---|
| Runs on my machine? | Confirmed | Yes, every check runs on your device | https://writewithharper.com | 2026-10-15 |
| Code licence | Confirmed | Apache-2.0 | https://writewithharper.com | 2026-10-15 |
| Model weights licence | Confirmed | No separate model weights | https://writewithharper.com | 2026-10-15 |
| Commercial use | Confirmed | Yes, Apache-2.0 | https://github.com/Automattic/harper/blob/master/LICENSE | 2026-10-15 |
| Paid services needed? | Confirmed | None required | https://writewithharper.com | 2026-10-15 |
| Hardware | Unknown | Not documented; the README claims under 1/50th of LanguageTool's memory footprint | https://github.com/Automattic/harper#readme | 2026-10-15 |
| Operating systems | Confirmed | Windows, macOS and Linux binaries (x64 and ARM), plus Chrome and Firefox extensions | https://github.com/Automattic/harper/releases/tag/v2.12.0 | 2026-10-15 |
| Setup effort | Confirmed | Easy; browser extension, editor extension or prebuilt binary | https://github.com/Automattic/harper#links | 2026-10-15 |

GitHub: 16470 stars, 741 forks, last push 2026-10-16, archived: no.
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Source: RepoQuarry (https://repoquarry.dev/projects/harper). Data licence: CC BY 4.0. Quotes are from project documentation and belong to their authors.