LanguageTool is an AI-based grammar, style, and spell-checker tool that checks text for errors and provides suggestions for corrections. It is available as a browser add-on, desktop app, and email add-on, and supports multiple languages and dialects. The tool helps improve writing by suggesting corrections for grammar, punctuation, style, and word choice. It also includes a paraphrasing feature to help reword sentences and makes text sound more professional and fluent. LanguageTool offers both free and premium versions, with the latter providing more advanced features for error checking and text analysis.