Website & Development · Chrome Extensions & Browser Tools

Harper Grammar Checker

Free, open-source English grammar and spell checker from Automattic that runs entirely on your device, 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.

Best forPrivate grammar checks

ReviewedOct 2026Free

7.65 criteria · see breakdown

Try HarperFree, open source

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.

Our score

Reviewed by the Conversion Gems editorial team. Hover a facet to focus it; click to pin.Tap a facet to focus it.

What it is, and why we rate it

One line each. Open a row for detail.

What it really isA free, rule-based English grammar and spell checker that runs locally in browsers, code editors and on macOS.

Our takeHarper 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 itIt gives private, fast grammar checks at no cost in many of the places people write.

The catchEnglish only, no AI rewriting, and the desktop app is macOS only.

Best / not good for

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

Trade-offs

Friction report

Trade-offs to know before signing up.

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.

Still a fit?

If none of these block you, start on the free plan.

Try Harper

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

Is the Harper grammar checker free?

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.

Does Harper use AI?

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.

Is Harper safe to use?

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.

Does Harper work with Google Docs?

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.

Is Harper better than Grammarly?

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.

Is Harper available on Windows?

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.