LanguageTool languagetool-org/languagetool

Rule-based grammar, spelling and style checker for 25+ languages; the core and HTTP server are open source (LGPL), Premium and AI rules are not.

Creator kit + Compare GitHub ↗ Install guide (official) ↗

LanguageTool at a glance

Checked 15 Oct 2026

LanguageTool checks grammar, spelling and style in English, Spanish, French, German, Portuguese, Polish, Dutch and 20+ other languages. The open-source core (LGPL-2.1+, latest tag v6.8) runs as a Java command-line tool, desktop GUI or local HTTP server that editor plugins can point at. A self-hosted server has no AI-based rules (cloud only) and no synonyms; Premium, the hosted service and the browser add-on are separate. Optional ~8GB n-gram data improves confusable-word checks. No AI rewriting or plagiarism check.

Cite this pageRepoQuarry. “LanguageTool.” Checked 15 Oct 2026. https://repoquarry.dev/projects/languagetool

How much of Grammarly does it replace?

2 of 5 jobs. Rule-based grammar, spelling and style checks in many languages; no AI rewrite, tone changes or plagiarism check when self-hosted.

Grammar and spelling checks Partial replacement

Style and clarity suggestions Partial replacement

AI rewriting and tone changes Not covered

Works in the browser and other apps Not covered

Plagiarism check Not covered

For AI rewriting and tone changes, works in the browser and other apps, plagiarism check, see other Grammarly alternatives. You may also need to build an interface, an API server and hosting yourself.

Facts, with sources

Every answer links to where we found it. We read the documentation; we did not install it.

Report a correction

QuestionAnswerSourceChecked

Runs on my machine? Yes, as a local Java server, CLI or desktop GUI; the hosted cloud service is separate LanguageTool comes with its own embedded HTTP server, so you can send a text to a local instance of LanguageTool. dev.languagetool.org · http-server ↗ 1d ago

Code licence LGPL-2.1 or later (the core in this repo); Premium is not open source The LanguageTool core (this repo) is freely available under the LGPL 2.1 or later. github.com · languagetool#readme ↗ 1d ago

Model weights licence No separate model weights in the open-source core; AI-based rules exist only in the cloud service This will give you a basic LanguageTool server without AI-based rules. The AI-based rules are only available in the cloud. dev.languagetool.org · http-server ↗ 1d ago

Commercial use Yes, LGPL conditions apply if you modify and distribute the core github.com · COPYING.txt ↗ 1d ago

Paid services needed? None required to self-host; AI-based rules and Premium features are paid cloud extras The AI-based rules are only available in the cloud. dev.languagetool.org · http-server ↗ 1d ago

Hardware Needs Java; optional n-gram data is ~8GB and should sit on an SSD; RAM needs not documented Make sure you have a fast disk, i.e. an SSD. dev.languagetool.org · finding-errors-using-n-gram-data ↗ 1d ago

Operating systems Java app for Linux, macOS (Homebrew) and Windows; on Windows fastText language detection is unavailable on Windows, fastText is not available and LanguageTool's language detection will not work that well dev.languagetool.org · http-server ↗ 1d ago

Setup effort Medium; unzip the snapshot and start the server with Java, or use a community Docker image This approach is only supposed to be used by advanced users who are familiar with using the command line. dev.languagetool.org · http-server ↗ 1d ago