Open Source Grammarly Alternatives
A curated collection of the 2 best open source alternatives to Grammarly.
The best open source alternative to Grammarly is Harper. If that doesn't suit you, we've compiled a ranked list of other open source Grammarly alternatives to help you find a suitable replacement. Other interesting open source alternative to Grammarly is LanguageTool.
Grammarly alternatives are mainly Browsers & Extensions. Browse these if you want a narrower list of alternatives or looking for a specific functionality of Grammarly.
An English grammar checker that runs entirely on your machine, built for writers and developers who want suggestions without a cloud round trip.
Harper is an English grammar checker written by someone tired of the alternatives. Paid cloud checkers send everything you write to a remote server and add a network round trip to every revision, while heavyweight local tools ask for gigabytes of memory and a sixteen gigabyte n-gram dataset. Harper lints a document in milliseconds and uses less than a fiftieth of the memory LanguageTool needs.
Everything stays on your machine, and the core is small enough to ship as WebAssembly, so the same checker can run inside a browser. The project treats slow linting as a defect and asks people to file significant performance problems as bugs.
Harper reaches writers through several front ends rather than one application.
- harper-ls: a language server that plugs the checker into Visual Studio Code, Neovim, Helix, Emacs and Zed.
- harper.js: a JavaScript package for embedding grammar checking in web pages and applications.
- Obsidian support: documented integration for checking notes without leaving the editor.
- Nothing leaves the device: no text is sent to a third party for analysis, so private drafts stay private.
- English only for now: the core is extensible to other languages, and contributions adding them are welcome.
The project suits anyone who drafts prose inside an editor rather than a web application, and who would rather not trade privacy or memory for correction. Documentation covers each editor integration, and the contribution guide is the starting point for fixes and for language support beyond English.
An open source proofreading engine for more than 25 languages, for writers and developers who want checking on a server they control.
LanguageTool catches the mistakes a spell checker cannot see, the ones that need grammar and style rules instead of a dictionary lookup. It covers English, Spanish, French, German, Portuguese, Polish and Dutch, plus more than twenty other languages.
The core in this repository is a Java library, usable in three shapes: called directly through the Java API, run as an HTTP server of your own, or reached through the project's public server for light use. Detection rules come from contributors, and the development documentation explains how to write new ones.
Installation offers several routes depending on what you want.
- Install script: a shell script installs or builds, with flags for a quiet run, a chosen package and clean removal.
- Packages: standalone, Wikipedia and an office extension for LibreOffice and OpenOffice build separately.
- Run modes: the same install runs as a graphical app, a command line checker or a server.
- Docker: no official image, though three community-maintained ones are listed.
- Building: Java 17 and Maven, with a shallow clone advised since a full one pulls more than 500 MiB.
The core is distributed under LGPL 2.1 or later. Running your own instance is the point for anyone who cannot send drafts to a third party, and the HTTP API is documented the same way for a private server and the public one, so an editor integration written against either keeps working.
