strong2026
Massive HN reception — 645pts, highest in categoryOverwhelming demand for privacy-first, open-source Grammarly alternative. Highest engagement of any tool in the content-writing category on HN.
645pts / 162 commentsHN developer community
← All solutions
Harper
activeOpen-source, privacy-first grammar checker built in Rust + WebAssembly. Sub-10ms on-device processing. Browser extensions (Chrome, Firefox), editor plugins (VS Code, Neovim, Obsidian, WordPress). Backed by Automattic. Apache 2.0.
Score 85
Where it wins
10,111 GitHub stars — nearly 2x Vale's stars
HN: 645pts/162 comments — highest engagement in entire content-writing category
Backed by Automattic (WordPress parent company)
Sub-10ms on-device processing via Rust + WebAssembly — best performance in category
Browser extensions: Chrome, Firefox. Editor plugins: VS Code, Neovim, Obsidian, WordPress
Apache 2.0 license — fully open-source
Where to be skeptical
English-only — no multilingual support (LanguageTool wins here)
Grammar checking only — no style guides, no tone analysis, no AI rewriting
Different tool than Vale — grammar vs style enforcement, not a replacement
358 open issues — growing maintenance load
Editorial verdict
Best privacy-first grammar checker for developers. 10,111 stars (2x Vale), HN 645pts (highest in entire content-writing category). Backed by Automattic. English-only, grammar-only — no style guides, no AI rewriting. Different tool than Vale: grammar vs style enforcement.
Related
LanguageTool
84Open-source multilingual grammar and style checker supporting 30+ languages. Self-hostable, SOC 2 compliant, GDPR-friendly. Free tier + Premium from $4.99/mo. Written in Java. 14,184 GitHub stars — highest in content-writing category.
Vale
80Open-source prose linter for docs-as-code pipelines. Markup-aware (Markdown, reStructuredText, AsciiDoc, HTML), CI/CD-native, extensible style packages (Microsoft, Google, write-good). Written in Go.
proselint
72Prose linter based on advice from world-class writers and editors. 4,519 GitHub stars but 247 open issues signals maintenance debt. Vale has a proselint-compatible package.
Copy.ai
45AI-powered marketing workflow automation platform. Moves beyond single-shot copy generation into multi-step automated pipelines — chain AI actions, web scraping, CRM updates, and third-party integrations.
Public evidence
strong2026
XDA Developers endorsement'I've ditched Grammarly for this open-source alternative and it's amazing.' High-profile endorsement from trusted tech publication.
Major tech publication featureXDA Developers
strongSelf-reported2026
Performance claim — sub-10ms on-deviceHarper runs entirely on-device using Rust and WebAssembly and returns suggestions in under 10 milliseconds. Privacy + speed are core value props.
README documentationAutomattic/Harper team
moderate2026
Limited to English, no AI rewritingHarper skips many premium features: tone analysis, genre-specific style guides, AI-powered rewrites. Grammar only, not full writing assistant.
Independent open-source publicationIt's FOSS (independent)
Raw GitHub source
GitHub README peek
Constrained peek so you can sanity-check the source material without leaving the site.
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<img src="https://raw.githubusercontent.com/Automattic/harper/master/logo.svg" width="400px" />
<h1>Harper</h1>
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View on GitHub →
Harper is an English grammar checker designed to be just right. I created it after years of dealing with the shortcomings of the competition.
Grammarly was too expensive and too overbearing. Its suggestions lacked context, and were often just plain wrong. Not to mention: it's a privacy nightmare. Everything you write with Grammarly is sent to their servers. Their privacy policy claims they don't sell the data, but that doesn't mean they don't use it to train large language models and god knows what else. Not only that, but the round-trip-time of the network request makes revising your work all the more tedious.
LanguageTool is great, if you have gigabytes of RAM to spare and are willing to download the ~16GB n-gram dataset. Besides the memory requirements, I found LanguageTool too slow: it would take several seconds to lint even a moderate-size document.
That's why I created Harper: it is the grammar checker that fits my needs. Not only does it take milliseconds to lint a document, take less than 1/50th of LanguageTool's memory footprint, but it is also completely private.
Harper is even small enough to load via WebAssembly.
Language Support
Harper currently only supports English, but the core is extensible to support other languages, so we welcome contributions that allow for other language support.
Performance Issues
We consider long lint times bugs. If you encounter any significant performance issues, please create an issue on the topic.
If you find a fix to any performance issue, we would appreciate the contribution. Just please make sure to read our contribution guidelines first.
Links
- Frequently Asked Questions
- Obsidian Documentation
harper-lsDocumentation- Supported Editors' Documentation
- Visual Studio Code
- Neovim
- Helix
- Emacs
- Zed
harper.jsDocumentation- Official Discord Server
Huge Thanks
This project would not be possible without the hard work from those who contribute.
<a href="https://github.com/automattic/harper/graphs/contributors"> <img src="https://contrib.rocks/image?repo=automattic/harper" /> </a>Harper's logo was designed by Lukas Werner.