Harper is a free, open-source grammar and spell checker for English that runs entirely on your device. It suits writers and developers who want checks in their browser, code editor or Mac apps without sending text to a server. There is no paid plan, and Harper uses no large language model.
Harper is now part of Automattic
Automattic, the company behind WordPress.com, acquired Harper and brought its creator Elijah Potter onto the team. Matt Mullenweg announced the move on 21 November 2024.
Harper remains free and open source under the Apache-2.0 license, and development continues in the Automattic/harper repository on GitHub.
Checked October 4, 2026
The bottom line
The best free option for private grammar checks in English; not a full writing assistant.
7.6
Our score
7.6 / 10
Conversion Gems editorial verdict
Free, open source
Features6/10
6 - solid grammar and spelling checks in five English dialects, but no rewriting, tone or other languages per Harper's site.
Value10/10
10 - completely free and open source with no paid tier.
Ease of use8/10
8 - install an extension or plugin with no account; editor setups may need a language server.
Ecosystem8/10
8 - Chrome, Firefox, VS Code, Neovim, Helix, Emacs, Sublime, Zed, Obsidian, WordPress, harper.js and a language server.
Support5/10
5 - documentation and public GitHub issues; no support desk.
What it really is
A free, rule-based English grammar and spell checker that runs locally in browsers, code editors and on macOS.
Our take
Harper is an easy pick if privacy matters or you write in code editors and Markdown. It catches mechanical errors quickly but does not rewrite or restyle text, so heavy editors may still pair it with another tool.
Why we rate it
It gives private, fast grammar checks at no cost in many of the places people write.
The catch
English only, no AI rewriting, and the desktop app is macOS only.
Best for
Developers writing docs in code editors
Privacy-conscious writers
Obsidian and Markdown users
Not good for
Non-English writing
Users who want AI rewrites or tone suggestions
Friction report
Time to value
Install the browser extension or editor plugin and it works in minutes.
Scale breakpoint
No paid tiers or seat limits; teams wanting central admin or style guides have no managed option.
Walled garden
None: open source, local, no account.
Where Harper works
Surface
Options
Notes
Browsers
Chrome, Firefox, Edge
Includes Google Docs through a bridge script
Code editors
VS Code, Neovim, Helix, Emacs, Sublime Text, Zed
Via plugins or the Harper language server
Apps
Obsidian, WordPress
Plugin integrations
Desktop
Harper Desktop for macOS
macOS 14 or later; Windows on the roadmap
Developers
harper.js, language server
Embed Harper in your own tools
From Harper's website and documentation, checked 4 October 2026. All options are free.
Frequently Asked Questions
Yes. Harper is free and open source under the Apache-2.0 license, with no account or credit card needed (checked 4 October 2026). The macOS desktop app is free too.
Harper's site says there is no LLM in the loop. It is a rule-based checker written in Rust that runs on your device.
Harper states that every check happens locally, with no cloud round-trips and no telemetry, so your text does not leave your device. The code is public on GitHub under Automattic.
Yes, through the browser extension. Harper's docs explain it uses a bridge to Google Docs' internal text APIs; some users have reported issues such as fixes not applying automatically.
It depends on what you need. Harper is free and keeps text on your device, but it is English only and has no AI rewriting. Grammarly's plans add AI prompts, tone detection and, on Pro, plagiarism checks.
The browser extensions and editor plugins work on Windows, but Harper Desktop is macOS only for now. Harper says other platforms are on the roadmap.
Harper Grammar Checker alternatives
Other writing checkers to compare:
Grammarly: Writing assistant with grammar, tone and AI writing features on free and paid plans.
QuillBot: Paraphrasing and grammar tools in the browser.
Hemingway Editor: Readability-focused editor that highlights hard-to-read sentences.
Sapling.ai: AI writing assistant aimed at support and sales teams.
