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Harper
What it is
Harper is a free, open-source writing checker that flags spelling, capitalization, grammar errors, and awkward phrasing, with style suggestions also available. Its checks run locally; the maker says it has no cloud round-trips, telemetry, or LLM in the loop. Harper supports English and British, American, Canadian, Australian, and Indian English dialects. It can be used through browser and editor extensions, a language server, a JavaScript library, a Rust crate, and native apps. Listed integrations include Chrome, Brave, Edge, Firefox, VS Code, Cursor, Obsidian, WordPress, Neovim, Zed, Helix, Emacs, and Sublime Text. Harper Desktop lets users toggle rules, add dictionary entries, select an English dialect, and enable checking per app. The desktop app is listed as beta for macOS 14 or later on Apple Silicon and Intel; a Windows desktop beta is also available. The maker says suggestions arrive in under 10 ms. The free plan costs nothing, and no account or credit card is required.
For and against
For
- Checks spelling, grammar, capitalization, and phrasing.
- Processes checks locally.
- Supports multiple English dialects.
- Offers browser and editor integrations.
- No account or credit card required.
Against
- Language support is limited to English dialects.
- macOS and Windows desktop apps are labeled beta.
- Windows beta may show an unsigned-app warning.
- Does not run in Gmail unless its built-in checker is disabled.
The verdict
Harper offers grammar and spelling checks with style suggestions across browser, editor, and desktop options. Its listed language support is English dialects, and the desktop releases have beta limitations.
Who it suits
Harper suits students, journalists, and developers seeking writing checks with local processing. Its browser, editor, and desktop options offer several ways to use it.
Plans and prices
Free
all features · local processing · no credit card
Read 14 Oct 2026 · writewithharper.com
Harper
No account or credit card required · Apache-2.0 open source
Read 7 Oct 2026 · writewithharper.com
On the record
- API and SDKs
- Developers can integrate harper.js as a JavaScript library, harper-core as a Rust crate, or harper-ls through the Language Server Protocol.writewithharper.com · read 14 Oct 2026
- Apps
- Listed integrations include Chrome, Brave, Edge, Firefox, VS Code, Cursor, Obsidian, WordPress, Neovim, Zed, Helix, Emacs, and Sublime Text.writewithharper.com · read 7 Oct 2026
- Browser extension
- Yeswritewithharper.com · read 20 Sep 2026
- Chrome Web Store privacy
- The Chrome Web Store listing says the developer does not collect or use user data.chromewebstore.google.com · read 14 Oct 2026
- Customization
- Harper Desktop lets users toggle rules, add dictionary entries, choose an English dialect, and enable checking per app.writewithharper.com · read 7 Oct 2026
- Desktop app
- Yeswritewithharper.com · read 20 Sep 2026
- Desktop availability
- The Harper Desktop page lists macOS 14 or later on Apple Silicon and Intel and labels the app beta.writewithharper.com · read 7 Oct 2026
- Documentation depth
- Documentation includes integration guides, harper.js API material, Weir rule language documentation and contributor build/testing guides.writewithharper.com · read 14 Oct 2026
- Feature: code comments
- Harper can lint comments and documentation in many programming and markup languages through harper-ls.writewithharper.com · read 14 Oct 2026
- Feature: custom rules
- The Weir language lets users and organizations define custom linguistic rules and conventions.writewithharper.com · read 14 Oct 2026
- Feature: dictionaries
- The language-server integrations support custom dictionaries and code actions for adding words.writewithharper.com · read 14 Oct 2026
- Feature: grammar suggestions
- Harper underlines detected errors and offers suggested corrections while users write.writewithharper.com · read 14 Oct 2026
- GitHub project scale
- The public repository showed about 16.4 thousand stars, 720 forks and more than 800 open issues when accessed.github.com · read 14 Oct 2026
- Gmail limitation
- Harper will not run in Gmail unless Gmail’s built-in grammar checker is disabled.writewithharper.com · read 7 Oct 2026
- Integration: browsers
- Official browser integrations are available for Chrome, Brave, Microsoft Edge and Firefox.writewithharper.com · read 14 Oct 2026
- Integration: editors
- Official editor integrations include VS Code, Cursor, Neovim, Zed, Helix, Emacs and Sublime Text.writewithharper.com · read 14 Oct 2026
- Integrations
- The maker lists browser and editor extensions, a language server, a JavaScript library, a Rust crate, and native apps.writewithharper.com · read 7 Oct 2026
- Integration: writing apps
- Harper provides plugins or integrations for Obsidian, WordPress and a macOS desktop application.writewithharper.com · read 14 Oct 2026
