RedPen

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What RedPen is

RedPen is an open-source proofreading tool for writers and programmers creating technical documents or manuals that need to follow a writing standard. It checks natural-language text rather than source code, and validates markup in formats such as Markdown, Textile, AsciiDoc, reStructuredText, and LaTeX. The maker says it handles documents in languages including English, German, Japanese, and Chinese. Users select validators and add them to a configuration file; checks issue warnings. RedPen can run from the command line, and its REST API and user interface provide other ways to use validation. Integrations and packages cover Atom, Emacs, Vim, WordPress, IntelliJ IDEA, Sublime Text, and Visual Studio Code. The IntelliJ plugin adds validation as an editor inspection, while the WordPress plugin checks posts as they are written and can highlight errors. The WordPress plugin uses a public RedPen server by default, or can be configured for a user's own server. The project also supports JavaScript extensions, custom style guides, and terminology management. It runs on Linux, macOS, and Windows, and the maker links to a mailing list and chat room for support.

Who it suits

RedPen suits writers and programmers who need consistent style and terminology in technical documents or manuals. It is also relevant to people who want to run checks in a command-line or CI workflow, use an editor integration, or validate documents through the REST API.

What it does well

Open-source and free to use.
Checks natural-language text in several markup formats.
Supports custom style guides and terminology management.
Integrations include WordPress, IntelliJ IDEA, and Visual Studio Code.
JavaScript extensions and REST API are available.

What to know first

Checks issue warnings rather than describing an automatic correction action.
IntelliJ support for some formats requires relevant plugins.
Active configuration of validators uses a configuration file.

Getting started

Visit https://www.redpen.cc/ for the project.
Choose a supported platform: Linux, macOS, or Windows.
Select validators and add them to a configuration file.
Use the command line, REST API, user interface, or a listed editor integration.
For WordPress, use the plugin with the public server or configure your own RedPen Server.

Verdict

Choose RedPen if you need configurable style and terminology checks across technical documents and supported editors. Look elsewhere if you need a rule action beyond warnings or a proofreading tool focused on programming languages.

Questions

Does RedPen cost anything?

RedPen is listed as free and open source. Its repository identifies the license as Apache-2.0.

Which document formats does it validate?

Supported markup formats include Markdown, Textile, AsciiDoc, reStructuredText, and LaTeX. The editor support list also includes Re:VIEW and Wiki.

Which languages can RedPen check?

The maker says it works with documents in languages including English, German, Japanese, and Chinese.

Can I use RedPen in an editor?

Integrations or packages are listed for Atom, Emacs, Vim, WordPress, IntelliJ IDEA, Sublime Text, and Visual Studio Code. The IntelliJ plugin adds validation as an editor inspection.

Does RedPen offer an API?

Yes. RedPen has a REST API, and RedPen Server provides endpoints to validate documents with preset or user-supplied configuration.

Where can I get support?

The maker's site links to a mailing list and chat room for contact and support.

Facts from RedPen's own pages

API and UI: The project README links to a REST API and user interface. · github.com, 8 Oct 2026
Audience: RedPen is described as a tool for writers or programmers producing technical documents or manuals that must follow a writing standard. · redpen.cc, 8 Oct 2026
Command-line and CI: A maker blog describes running RedPen from the command line in a Travis CI workflow to check document quality. · blog.redpen.cc, 8 Oct 2026
Customization: Users can choose validators and add them to a configuration file. · redpen.cc, 8 Oct 2026
Document formats: It validates markup text including Markdown, Textile, AsciiDoc, reStructuredText, and LaTeX. · redpen.cc, 8 Oct 2026
Extensions: The project supports a plugin system that lets users write extensions with JavaScript. · github.com, 8 Oct 2026
External validation: The WordPress plugin blog says it uses a public RedPen server by default and can be configured to use the user's own RedPen Server instance. · blog.redpen.cc, 8 Oct 2026
Formats: The site lists Markdown, Textile, AsciiDoc, reStructuredText, and LaTeX as supported markup formats. · redpen.cc, 8 Oct 2026
Integrations: The project lists integrations or packages for Atom, Emacs, Vim, WordPress, IntelliJ IDEA, Sublime Text, and Visual Studio Code. · github.com, 8 Oct 2026
JetBrains integration: The RedPen IntelliJ IDEA plugin adds text validation as an editor inspection and supports plain text, properties and resource bundles, Markdown, and AsciiDoc when relevant plugins are installed. · blog.redpen.cc, 8 Oct 2026
Languages: The maker says RedPen works with documents in languages including English, German, Japanese, and Chinese. · redpen.cc, 8 Oct 2026
License: The project repository identifies its license as Apache-2.0. · github.com, 8 Oct 2026
Natural-language checking: It automates checks on documents written in natural languages, rather than programming languages. · redpen.cc, 8 Oct 2026
Platforms: The project README lists macOS, Windows, and Linux as supported platforms. · github.com, 8 Oct 2026
Purpose: RedPen is a proofreading tool for writers and programmers who write technical documents or manuals that must follow a writing standard. · redpen.cc, 8 Oct 2026
REST API: The RedPen Server provides REST endpoints for validating documents with preset or user-supplied configuration. · blog.redpen.cc, 8 Oct 2026
Support: The maker's site links to a mailing list and chat room for contact and support. · redpen.cc, 8 Oct 2026
WordPress integration: The RedPen WordPress plugin validates posts while users type and can highlight errors in the editor. · blog.redpen.cc, 8 Oct 2026

Where RedPen stands on Freedom251

Writing Style Checkers#27 of 29