LanguageTool

LanguageTool is open-source proofreading software for English, Spanish, French, German, Portuguese, Polish, Dutch, and more than 20 other languages. It finds many errors that a simple spell checker cannot detect, covering grammar, punctuation, spelling, and style issues for multilingual writing.

It can be used through a public HTTP API, run as your own LanguageTool server, or embedded from Java. The core software is available for source builds with Java 17 and Apache Maven, and the service exposes an HTTP check endpoint for integrations that need automated text checking.

The LanguageTool core is freely available under LGPL 2.1 or later. Community-contributed Docker files and images are available, while the core source build requires Java 17 and Maven. Self-hosting is supported through the LanguageTool server.