| LanguageTool | |
|---|---|
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 LanguageTool WikiCheck | |
| Developers | Daniel Naber and Marcin Miłkowski |
| Initial release | 15 August 2005; 20 years ago (2005-08-15) |
| Stable release | 6.7[1]  / 10 October 2025 |
| Repository | |
| Written in | Java |
| Platform | Java SE |
| Size | |
| Type | Grammar checker |
| License | GNU LGPL v2.1+ |
| Website | languagetool |
LanguageTool is afree and open-sourcegrammar,style, andspell checker, and all its features are available for download.[4][5] The LanguageTool website connects to aproprietary sister project calledLanguageTool Premium (formerlyLanguageTool Plus), which provides improved error detection for English and German, as well as easier revision of longer texts, following theopen-core model.
LanguageTool was started by Daniel Naber for hisdiploma thesis[6] in 2003 (then written inPython). It now supports 31 languages, each developed by volunteer maintainers, usually native speakers of each language.[7] Based on error detection patterns, rules are created and then tested for a given text.The core app itself is free and open-source and can be downloaded for offline use. Some languages use 'n-gram' data,[8] which is massive and requires considerable processing power and I/O speed, for some extra detections. As such, LanguageTool is also offered as a web service that does the processing of 'n-grams' data on the server-side. LanguageTool "Premium" also usesn-grams as part of itsfreemium business model.
LanguageTool web service can be used via aweb interface in aweb browser, or via a specializedclient-sideplug-ins forMicrosoft Office,LibreOffice,TeXstudio,Apache OpenOffice,Vim,Emacs,Firefox,Thunderbird, andGoogle Chrome.[5]
LanguageTool does not check a sentence for grammatical correctness, but whether it contains typical errors. Therefore, it is easy to invent ungrammatical sentences that LanguageTool will still accept. Error detection succeeds with a variety of rules based on XML or written in Java.[9] XML-based rules can be created using an online form.[10]
More recent developments rely on large n-gram libraries that offer suggestions for improving misspellings with the help ofartificial neural networks.[11]
In April 2023Learneo acquired LanguageTool.[12][13][14][15]
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