head to head · open source
Harper vs LanguageTool
Harper has 15,469 GitHub stars, 632 forks, 896 open issues and last shipped yesterday. LanguageTool has 15,042 stars, 1,581 forks, 2,148 open issues and last shipped yesterday. Harper leads on adoption by 3% (15,469 vs 15,042 stars). Harper is written in Rust under Apache-2.0; LanguageTool is written in Java under LGPL-2.1. Harper has attracted 4% as many forks as stars, LanguageTool 11%. Harper was the more recently maintained of the two, and both are self-hostable with no licence fee.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| Harper | LanguageTool | |
|---|---|---|
| GitHub stars | ★ 15K | ★ 15K |
| License | Apache-2.0 | LGPL-2.1 |
| Written in | Rust | Java |
| Last push | 2026-09-17 | 2026-09-17 |
| Forks | ⑂ 632 | ⑂ 1.6K |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick Harper if
- You weight community size — 15K stars and counting
- You want the Apache-2.0 license terms
- Your stack matches Rust
- You value the larger contributor base for long-term maintenance
pick LanguageTool if
- You want the LanguageTool feature set and don't need the biggest community
- You prefer the LGPL-2.1 license terms
- Your stack matches Java
- You evaluated both and LanguageTool fits your workflow better
About Harper
Harper is offline, privacy first grammar checker for English. It lives in productivity, browser extension, developer tools, and text editing ecosystem. Project is open source under Apache 2.0. GitHub metadata shows 15373 stars, 627 forks, and 896 open issues. Last push is 2026 09 14. Category is Productivity & Utilities / Browsers & Extensions. It uses Rust for core, WebAssembly for browser loading, language server for editors, JavaScript package for web and Node.js apps. It solves slow, costly, network dependent grammar checking. It replaces Grammarly and LanguageTool as named in README. Grammarly sends writing …
read the full Harper overview →
About LanguageTool
LanguageTool is open source proofreading software for English, Spanish, French, German, Portuguese, Polish, Dutch, and more than 20 other languages. Its tagline describes it as an AI powered grammar checker for 30+ languages, while the repository description calls it a style and grammar checker for 25+ languages. The project lives in the natural language processing and productivity ecosystem, where it helps writers, editors, and applications detect errors that a simple spell checker cannot find.
read the full LanguageTool overview →
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Frequently asked questions
Is Harper or LanguageTool more popular?
Harper has 15,469 GitHub stars and LanguageTool has 15,042. Harper has the larger community by that measure.
Are Harper and LanguageTool free?
Both are open source. Harper is licensed under Apache-2.0 and LanguageTool under LGPL-2.1. Neither carries a licence fee.
What is the difference between Harper and LanguageTool?
Harper is written in Rust and LanguageTool in Java. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, Harper or LanguageTool?
Choose Harper if you want the larger community (15,469 stars) or its Apache-2.0 licence terms. Choose LanguageTool if its feature set, stack or LGPL-2.1 licence fits better. Both are self-hostable.