About LanguageTool
LanguageTool is a multilingual grammar and style checker that covers more than 30 languages. It began as an open-source grammar checker and is still best known for its rule-based engine, published under the LGPL on GitHub. The browser extension is a separate, closed-source product.
It checks spelling, grammar and style, and the free version works in most web text fields. Premium adds extra checks for several major languages, texts of up to 150,000 characters per field, AI paraphrasing and a custom style guide. The extension is made by LanguageTooler GmbH, a German company that Learneo bought in April 2023.
Know who owns it. Learneo is a US company that also owns QuillBot and Course Hero. Checking happens on LanguageTool's servers, so your text leaves your device. Its policy, updated 17 August 2026, says it does not use input from LanguageTool users to train its models, with no opt-out needed. That promise is specific to LanguageTool, and the same policy says its extensions may collect website content and metadata while you browse. The Chrome rating is a low 3.3. It suits multilingual writers, but turn it off on sites with sensitive text.
Pros and cons
- Supports more than 30 languages, far beyond English-only tools
- Free tier works on any site; Premium adds longer texts and AI paraphrasing
- Policy says LanguageTool users' inputs are not used to train its models
- Listed for Chrome, Firefox and Edge, and updated in October 2026
- Your text is sent to LanguageTool's servers to be checked
- Chrome rating is 3.3 from about 12,600 ratings, below Edge and Firefox
- The extension is closed source; only the core engine is open
Permissions
On Firefox it asks to read and change data on all websites, plus the active tab, scripting, alarms and context menus. It needs this to underline mistakes in any text field you type in.
