LanguageTool
LGPL-2.1 proofreading with explainable rules, run as your own HTTP server with an API, from the command line, or inside LibreOffice.
Know firstNo rewriting or tone changes, and a full build needs Java and over 1.5 GB of disk.
Writing and grammar5 projects, checked September 17, 2026
Open-source alternatives to Grammarly
The open-source alternatives to Grammarly are LanguageTool, Harper, Writing Tools, Vale and LTeX+. LanguageTool checks grammar in more than 25 languages and can run as your own server. Harper checks English in your editor in milliseconds. Writing Tools rewrites selected text in any application with a model you choose, including a local one. Vale enforces a team's own style guide in editors and continuous integration, and LTeX+ checks LaTeX and Markdown. All five can run without sending your writing anywhere.
- Grammar in more than 25 languages
- LanguageTool
- Fast English checking in your editor
- Harper
- AI rewriting anywhere on screen
- Writing Tools
5 of 5 carry an OSI licence. 5 of 5 run on your own machines. Figures read from GitHub on September 17, 2026.
Pick by need
One project per need, with the reason from its own README and the one thing to know before you choose it.
Harper
Apache-2.0 from Automattic, linting in milliseconds inside VS Code, Neovim, Helix, Emacs, Zed and Obsidian, or in the browser through WebAssembly.
Know firstEnglish only for now, and it checks rather than rewrites.
Writing Tools
GPL-3.0 system-wide assistant that proofreads, rewrites or changes tone in any app with one hotkey, using a local model through Ollama or a cloud one.
Know firstResults depend entirely on the model you choose, and Linux support is a work in progress.
Vale
MIT prose linter that turns writing guidelines into checks in editors and CI, understanding Markdown, AsciiDoc and code comments, entirely offline.
Know firstIt enforces the rules you give it, so it needs setting up, and it does not rewrite.
LTeX+ LS
MPL-2.0 language server checking 16 markup formats in 20+ languages with LanguageTool bundled, offline, in any editor that speaks the protocol.
Know firstNeeds an editor with language server support, and does no AI rewriting.
What to take away
- All five can run without sending your writing to a service.
- Only Writing Tools uses an AI model; the rest apply rules you can inspect.
- Vale is the one built for a team's own style guide, in editors and in CI.
- Grammarly still wins on checking and rewriting together in the browser and every app.
The projects, side by side
The facts that decide most choices. Each project's page carries the full panel.
| Project | Best for | Openness | Licence | Runs as | Own machines | Stars |
|---|---|---|---|---|---|---|
| LanguageTool | Grammar in more than 25 languages | OSI | LGPL-2.1 | Install script, HTTP server, Java API, Office extension | Yes | 15,046 |
| Harper | Fast English checking in your editor | OSI | Apache-2.0 | Language server (harper-ls), npm package (harper.js), Editor plugins, WebAssembly in the browser | Yes | 15,492 |
| Writing Tools | AI rewriting anywhere on screen | OSI | GPL-3.0 | Desktop app | Yes | 2,452 |
| Vale | A team's own style guide, enforced | OSI | MIT | Command line, CI, Editor integrations, Docker | Yes | 6,109 |
| LTeX+ LS | LaTeX, Markdown and Typst | OSI | MPL-2.0 | Language server, Command line | Yes | 256 |
Licence and star figures read from GitHub on September 17, 2026. Stars are shown as a dated fact and were not used to rank this page.
Each project, in turn
An LGPL-2.1 proofreading engine for English, Spanish, French, German, Portuguese, Polish, Dutch and more than 20 other languages, which you can run as your own HTTP server with an API, or inside LibreOffice.
LGPL-2.1 proofreading with explainable rules, run as your own HTTP server with an API, from the command line, or inside LibreOffice.
Know firstNo rewriting or tone changes, and a full build needs Java and over 1.5 GB of disk.
- Licence
- LGPL-2.1
- Runs as
- Install script, HTTP server, Java API, Office extension
- Platforms
- Anywhere Java 17 runs
- Hosted option
- Sold by the maintainers
- Last release
- No tagged release
An Apache-2.0 English grammar checker from Automattic that lints a document in milliseconds, uses a fraction of LanguageTool's memory by its own measure, runs privately in your editor or in the browser through WebAssembly.
Apache-2.0 from Automattic, linting in milliseconds inside VS Code, Neovim, Helix, Emacs, Zed and Obsidian, or in the browser through WebAssembly.
Know firstEnglish only for now, and it checks rather than rewrites.
- Licence
- Apache-2.0
- Runs as
- Language server (harper-ls), npm package (harper.js), Editor plugins, WebAssembly in the browser
- Platforms
- VS Code, Neovim, Helix, Emacs, Zed, Obsidian, Browser
- Hosted option
- None from the maintainers
- Last release
- v2.11.0, Sep 16, 2026
A GPL-3.0 system-wide writing assistant for Windows, Linux and macOS that rewrites, proofreads or summarises selected text anywhere with one hotkey, using a local model through Ollama or a cloud model with your own key.
GPL-3.0 system-wide assistant that proofreads, rewrites or changes tone in any app with one hotkey, using a local model through Ollama or a cloud one.
Know firstResults depend entirely on the model you choose, and Linux support is a work in progress.
- Licence
- GPL-3.0
- Runs as
- Desktop app
- Platforms
- Windows, Linux (work in progress), macOS 14 or later
- Hosted option
- None from the maintainers
- Last release
- Win_v9+mac_OS_v6.1, May 10, 2026
An MIT command-line prose linter that turns a team's writing guidelines into checks that run in an editor, in CI and beside code, offline, understanding Markdown, AsciiDoc and code comments rather than plain text.
MIT prose linter that turns writing guidelines into checks in editors and CI, understanding Markdown, AsciiDoc and code comments, entirely offline.
Know firstIt enforces the rules you give it, so it needs setting up, and it does not rewrite.
- Licence
- MIT
- Runs as
- Command line, CI, Editor integrations, Docker
- Platforms
- macOS, Windows, Linux, Docker
- Hosted option
- Sold by the maintainers
- Last release
- v3.22.0, Sep 17, 2026
An MPL-2.0 language server that checks grammar and spelling in LaTeX, Markdown, Typst, AsciiDoc and 12 other markup formats with LanguageTool, in more than 20 languages, offline, with Java and LanguageTool bundled.
MPL-2.0 language server checking 16 markup formats in 20+ languages with LanguageTool bundled, offline, in any editor that speaks the protocol.
Know firstNeeds an editor with language server support, and does no AI rewriting.
- Licence
- MPL-2.0
- Runs as
- Language server, Command line
- Platforms
- Any editor that speaks the Language Server Protocol, VS Code through the LTeX+ extension
- Hosted option
- None from the maintainers
- Last release
- 18.7.0, Jun 13, 2026
How to choose
The questions that settle it, in the order they usually come up.
Do you want corrections or rewriting?
LanguageTool, Harper, Vale and LTeX+ correct with explainable rules. Writing Tools rewrites with a model.
Which language do you write in?
LanguageTool covers 25+ and LTeX+ 20+. Harper is English only. Writing Tools follows its model.
Where do you write?
In an editor: Harper or LTeX+. In any app: Writing Tools. In documentation with a house style: Vale.
Where Grammarly is still the better choice
Grammarly, in the vendor's own words, is a service that "makes AI writing convenient" with "personalized AI guidance and text generation on any app or website", by its own description. grammarly.com. The cases below are where that still wins.
- You want checking and AI rewriting in one product, in the browser and every app, with nothing to set up.
- You want tone, clarity and plagiarism features together under one subscription.
- You want a browser extension maintained for every website you use.
- You want one vendor's suggestions rather than rules or a model you have to choose.
How this page was checked
Numbers from GitHub, dated
Stars, licence, last commit and last release are read from the GitHub API by a script every week and carry the date they were read. Nobody types them.
Claims from the README
What each project does is written from its own README and LICENSE, read in full on the date shown, and phrased as the project's claim. The sources are listed at the end.
What is never said
That a project is faster, better or cheaper than Grammarly. A price for anyone. A user count. A roadmap. If a fact is not on this page, it was not in the source.
- OSI Open source (OSI licence)
- The code, and the weights where the project is a model, carry a licence on the OSI approved list.
- Source available Source available
- The code is public, and the licence limits what you may do with it. Read the LICENSE file before commercial use.
- Open weights Open weights
- The model weights can be downloaded and run. The training data or code is closed, or the weights carry a restriction the code does not.
Questions people ask
What is the best open-source alternative to Grammarly?
It depends what you want from it. LanguageTool (LGPL-2.1) for grammar in 25+ languages, self-hosted. Harper (Apache-2.0) for fast English checking in editors. Writing Tools (GPL-3.0) for AI rewriting in any app. Vale (MIT) for enforcing a house style guide. LTeX+ (MPL-2.0) for LaTeX and Markdown.
Which ones rewrite text, rather than just flagging errors?
Writing Tools: select text anywhere, press a hotkey, and it proofreads, rewrites or changes tone with the model you choose, local or hosted. The others are rule-based, so they mark errors and suggest fixes, which makes each correction explainable and repeatable.
Can I check my writing privately?
Yes, all five run locally. Harper runs in the editor or the browser, Vale is a local binary that uploads nothing, LTeX+ bundles its checker and Java for offline use, LanguageTool can run as your own server, and Writing Tools can use a local model through Ollama.
Which support languages other than English?
LanguageTool covers more than 25 languages, LTeX+ more than 20 using the same engine, and Writing Tools works in any language its model handles. Harper is English only for now, by its README. Vale checks against rules you write, in any language.
Is there one for a documentation team?
Vale. It turns a team's writing guidelines into checks that run in editors and in continuous integration, understands Markdown, AsciiDoc and code comments, and ships published style guides from Microsoft, Google and Red Hat alongside your own terms.
Sources
- Grammarly homepage, the vendor's own description, read September 17, 2026
- LanguageTool README, read September 17, 2026
- Harper README, read September 17, 2026
- Writing Tools README, read September 17, 2026
- Vale README, read September 17, 2026
- LTeX+ README, read September 17, 2026
Running one of these inside your own environment, with your own data and your own security rules, is the kind of work Reveneau does. Read how a forward deployed engagement works.