AI Grammar Checker 2026: LanguageTool (15k Stars) - The Free Open Source Alternative to Grammarly

Grammarly Premium costs $12/month and your writing flows through their servers. LanguageTool gives you grammar checking in 30+ languages, open source and self-hostable - here is the honest 2026 comparison.

## The short answer **LanguageTool** (14,757 stars) is the leading open-source grammar checker in 2026: rule-based engine plus AI models, 30+ languages, browser extensions, desktop apps, and a self-hostable server. For privacy-conscious writers and non-English speakers, it beats Grammarly on coverage and price. ## What LanguageTool offers - **30+ languages**: real grammar checking in German, French, Spanish, Chinese, and more - not just English. - **Rule-based + AI**: traditional language rules catch what LLMs miss (style consistency, punctuation), while their AI adds context-aware rephrasing. - **Everywhere**: browser extensions (Chrome, Firefox, Edge), Word/Google Docs add-in, desktop app, and a REST API. - **Self-hostable**: the community server runs on your own infrastructure - your text never leaves your network. - **Free tier is genuinely useful**: grammar and spelling corrections are free; style suggestions need Premium. ## Quick start (self-host) ```bash docker run --rm -p 8081:8081 --name languagetool -e langtool_languageModel=/ngrams erosmariandri/languagetool # then POST text to http://localhost:8081/v2/check ``` Or just install the browser extension and use the free public server. ## Grammarly vs LanguageTool (2026) | Aspect | LanguageTool | Grammarly | |:-------|:-------------|:----------| | Price | Free / Premium $4.99-7.49 | Free / $12/mo | | Languages | 30+ | English only | | Privacy | Self-host option | Cloud only | | Open source | Yes | No | ## FAQ **Is the free version enough?** For grammar and spelling: yes. Style and tone suggestions need Premium, but the free tier covers most everyday writing. **How accurate is it?** Very good on grammar rules; comparable to Grammarly on common errors, better on non-English text. **Can I use it with sensitive documents?** Self-host the server and your text never leaves your machine. ## Related - [AI Writing Tool Free 2026](/post/ai-writing-tool-free-2026-6-best) - [AI Translation Tools 2026](/post/ai-translation-tools-2026-20260802)