Open-source ProWritingAid alternatives

LanguageTool is open-source proofreading software that finds grammar and style errors a simple spell checker would miss. It supports English, Spanish, French, German, Portuguese, Polish, Dutch and more than 20 other languages. The core is written in Java and freely available under the LGPL 2.1 or later.

It can be used in several ways. The project documents how to run your own LanguageTool server, an HTTP API for sending text to a server, a public server that can be used over HTTP, and a Java API with Javadoc. Error detection works through rules, and the development overview explains how to contribute new rules for a language.

Community-contributed Docker files are listed for people who want to run a containerized server. Building from source needs Java 17 and Apache Maven, and the README offers a scripted install as well as a shallow clone option to reduce download size, since a complete clone is large. A forum is available for questions.

RedPen is a proofreading tool for people who write technical documents or manuals that must follow a writing standard. It automates verification of natural-language text so that style and consistency rules are applied the same way every time, like a linter for documentation.

It is language independent and highly customizable, runs on macOS, Windows and Linux, and understands several markup formats including wiki text, Markdown, Textile, AsciiDoc, LaTeX, Re:VIEW and reStructuredText. A plugin system lets users write extensions in JavaScript, errors can be suppressed through annotations, and there is a REST API and web UI.

The ecosystem includes a Docker image, a RubyGem and a Python client, plus editor integrations for Atom, Emacs, Vim, IntelliJ IDEA, SublimeLinter and Visual Studio Code, and a WordPress plugin. RedPen is written in Java, licensed under Apache-2.0 and supported by ATL, with docs in English and Japanese.