LanguageTool

LanguageTool is an open-source grammar, style, and spell-checking tool that stands out for its exceptional multilingual support, covering over 30 languages including English, German, French, Spanish, Portuguese, Dutch, Polish, Russian, and many more with deep, native-quality rule sets for each. Unlike competitors that treat non-English languages as an afterthought with superficial coverage, LanguageTool provides genuinely thorough checking for each supported language with thousands of language-specific rules developed and maintained by professional linguists and an active open-source community. The tool is available as a browser extension for Chrome, Firefox, Safari, and Edge, plus dedicated add-ins for Microsoft Word, Google Docs, LibreOffice, Apple Mail, and a full-featured web editor for standalone use. A key differentiator is its privacy-first approach — the core engine is completely open source under LGPL, and organizations can self-host it on their own servers to ensure sensitive text never leaves their infrastructure, a critical requirement for legal firms, government agencies, and healthcare organizations. The Premium version adds advanced style suggestions, picky mode for refined and polished writing, word frequency analysis to catch repetition, an extended personal dictionary, and team features for organizational deployment. LanguageTool detects commonly confused words in context, flags false friends between languages for multilingual writers, and identifies register mismatches where formal and informal language are inappropriately mixed. The AI-powered paraphrasing feature suggests alternative phrasings for entire sentences, helping writers find clearer or more concise ways to express their ideas. With pricing starting at just $4.99 per month for Premium, it is one of the most affordable comprehensive grammar tools available. The enterprise API allows seamless integration into custom applications, CMS platforms, and internal tools with flexible per-request pricing.