Alternatives / Grammarly
Looking for an open source Grammarly alternative? We compared 2 open source grammar checkers by license, languages, privacy, self-hosting, and editor integrations. Harper is a fast, offline English checker, and LanguageTool supports 25+ languages but needs more resources.
Written by Maxime DERAME
Last updated:
| Alternative | Best for | License |
|---|---|---|
| Harper | Fast, offline, private English checking | Apache-2.0 |
| LanguageTool | Many languages and a self-hosted server | LGPL-2.1 |
We looked for open-source tools that overlap with Grammarly's core: checking grammar, spelling, and style as you write, in your editor or browser. We verified each project's license, recent activity, stars, languages, and self-hosting in its repository. Only two projects are mature enough to compare, and neither matches Grammarly's AI rewriting and tone suggestions. See our methodology for the full criteria.
Harper and LanguageTool are rule-based grammar and spelling checkers. They catch errors and style issues, but they do not rewrite paragraphs, adjust tone, or generate text the way Grammarly's AI features do. LanguageTool's AI-based suggestions are part of its paid premium service.
Harper is a Rust grammar checker that runs locally and lints a document in milliseconds with a small memory footprint. It supports English only. It integrates with Visual Studio Code, Neovim, Helix, Emacs, Zed, and Obsidian, and can also run in the browser through WebAssembly. Nothing you write leaves your device.
LanguageTool checks grammar, spelling, and style in 25+ languages and offers browser extensions and an HTTP server you can run yourself, so text stays on your infrastructure. Its best accuracy for some languages relies on large n-gram datasets of about 16 GB, and it needs far more memory than Harper. Its premium service adds AI-based and extra features that are not part of the open-source core.
Harper is licensed under Apache-2.0. LanguageTool is licensed under LGPL-2.1, and you can self-host the server for free, while the paid LanguageTool Premium offers additional proprietary features.
Both projects were updated within days of this update. Harper released v2.12.0 on October 1, 2026, and LanguageTool had a commit on October 2, 2026.
Grammarly is a proprietary cloud service: everything you write is sent to its servers, its best features need a paid subscription, and its suggestions can be intrusive. Open-source alternatives let you check text offline or on your own server, avoid subscriptions, and keep drafts private, at the cost of fewer AI features such as full-sentence rewriting and tone detection.
| Alternative | Languages | License | Self-hosted | Best for |
|---|---|---|---|---|
| Harper | English | Apache-2.0 | Yes (offline) | Private, fast checking |
| LanguageTool | 25+ languages | LGPL-2.1 | Yes (HTTP server) | Multilingual writing |
Write in English and want instant, private checking
Harper runs offline in milliseconds with a small memory footprint, and works in VS Code, Neovim, Obsidian, and the browser.
Write in several languages
LanguageTool supports 25+ languages with browser extensions and a server you can host yourself, though it needs more memory.