Best Open Source Alternatives to Grammarly in 2026
Grammarly's Subscription Cost
Grammarly Pro costs $30/month on the monthly plan, or $12/month billed annually ($144/year). Teams plans run $15/user/month billed annually. For a 10-person writing team, that's $1,800/year.
Beyond cost, Grammarly processes everything you type through their servers. Every email draft, every document, every message — analyzed on Grammarly's infrastructure. For organizations handling confidential content, this is a concern.
Open source alternatives, especially self-hosted LanguageTool, provide robust grammar and style checking with no per-user fees and no data leaving your infrastructure.
TL;DR
- LanguageTool (14K+ stars): Best open source grammar and style checker. Self-hostable, 31 languages, LGPL licensed. The closest open source equivalent to Grammarly.
- Harper: Newer, extremely lightweight grammar checker designed for developer tools. Rust-based, embeds in Neovim, VS Code, Zed.
- Local AI with writing prompts: Using Ollama + a capable model (Llama 3.1, Qwen) as a writing assistant can exceed Grammarly's AI suggestions.
- LanguageTool Premium: At $4.99/month, the paid version is half Grammarly's price and still privacy-friendly.
LanguageTool — Best Open Source Grammar Checker
LanguageTool (14K+ GitHub stars) is the most complete open source grammar and style checker. It supports 31 languages — more than any commercial competitor — and the core server is LGPL licensed and fully self-hostable.
What Makes It Stand Out
Self-hosted for privacy: Run LanguageTool on your own server, and your text never leaves your infrastructure. This is the key differentiator for privacy-conscious organizations.
31 languages: English, German, French, Spanish, Portuguese, Polish, Dutch, Russian, and 22 more. Better multilingual support than Grammarly.
Grammar and style rules: Checks for grammar errors, punctuation, common style issues, repetition, passive voice overuse, and other writing quality indicators.
Open rules: LanguageTool's rules are open and extensible — add custom rules specific to your organization's writing guidelines.
Integrations: Browser extension (Chrome, Firefox, Safari), LibreOffice plugin, VS Code extension, and HTTP API for custom integrations.
Self-Hosting
LanguageTool's server is a Java application. The easiest deployment is Docker:
docker run -d \
-p 8010:8010 \
--name languagetool \
erikvl87/languagetool
Or with ngrams for enhanced English checking:
# Download ngrams (improves false positive rate)
# 3GB download - put in /tmp/languagetool-ngrams
docker run -d \
-p 8010:8010 \
-v /tmp/languagetool-ngrams:/ngrams \
-e Java_Xmx=1g \
erikvl87/languagetool \
--languageModel /ngrams
Then configure your browser extension to point at http://localhost:8010/v2 instead of LanguageTool's cloud servers.
API Usage
curl -d "language=en-US&text=Your text to check hear." \
http://localhost:8010/v2/check
Returns JSON with detected errors, their positions, and suggestions.
The Extensions Caveat
An important technical note: while the LanguageTool server is open source (LGPL), the browser extensions are closed source. When you self-host, you configure the extensions to point at your server — but the extension code that captures your text and sends it to your server is closed source. This is a meaningful distinction for truly paranoid privacy requirements.
For maximum privacy, use LanguageTool's API directly in your application rather than through the extensions.
LanguageTool Premium vs Grammarly
At $4.99/month, LanguageTool Premium is half the price of Grammarly Premium/Pro. It adds style rules, phrasing suggestions, and synonym suggestions beyond the open source core.
Best for: Organizations that need robust grammar checking with privacy requirements, multilingual teams, and anyone who wants to avoid Grammarly's subscription cost.
Harper — Best Lightweight Developer Tool
Harper is a newer grammar checker written in Rust, designed to be embedded in developer tools. It's smaller, faster, and more focused than LanguageTool.
What Makes It Stand Out
Extremely lightweight: Harper is ~7MB in size. Compare this to LanguageTool's Java server requiring 500MB+ RAM. Harper is designed to run locally within an editor process.
Editor integration: First-class support for:
- Neovim (via lsp)
- VS Code (extension)
- Zed (built-in)
- Harper Web (for web-based integration)
Instant feedback: Because it runs in-process with your editor, suggestions appear as you type with no network latency.
Offline: Completely offline — no network requests, no configuration, just install and run.
Focused on technical writing: Designed for developers writing documentation, comments, commit messages, and README files.
Best for: Developers who want grammar checking in their code editor without leaving the terminal or browser.
Using Local AI for Writing Assistance
For Grammarly's AI-powered writing improvement features (rephrasing, tone adjustment, clarity improvements), a local LLM can be surprisingly effective.
With Ollama
Set up a writing assistant with any capable model:
ollama pull llama3.1:8b
# Quick writing check
echo "Your text here" | ollama run llama3.1:8b \
"Please check this text for grammar errors, clarity, and style. Suggest improvements:"
Prompts for Specific Grammarly Features
Grammar and clarity check:
Review the following text for grammar errors, clarity, and readability. List specific issues and suggest corrections:
[YOUR TEXT]
Professional tone adjustment:
Rewrite the following to sound more professional and concise, while preserving the original meaning:
[YOUR TEXT]
Email improvement:
Improve this email for clarity, professional tone, and conciseness. Keep the same meaning:
[YOUR TEXT]
A local Llama 3.1 8B or Qwen2.5 14B model can produce suggestions comparable to Grammarly's AI features for most writing tasks.
Best for: Teams already running local AI for other purposes who want to add writing assistance without additional subscriptions.
LibreOffice + Grammar Extensions
For users who primarily need grammar checking in documents (not emails or browser):
LibreOffice is free and open source. Its built-in spell checker covers basic errors. Add:
- LanguageTool extension: Install the LibreOffice extension, point it at your self-hosted instance
- After the Deadline: Plugin with advanced style checking
This gives you a complete free office suite with privacy-respecting grammar checking for document work.
Cost Comparison
Grammarly Annual Costs
| Plan | Monthly (annual billing) | Annual |
|---|---|---|
| Free | $0 | $0 |
| Pro | $12 | $144 |
| Teams (10 users) | $15/user | $1,800 |
| Enterprise | Custom | Custom |
Open Source Alternatives
| Tool | Monthly | Annual |
|---|---|---|
| LanguageTool self-hosted (Hetzner CAX11) | $4 | $48 |
| Harper (embedded in editor) | $0 | $0 |
| Local Ollama for AI writing | $0-4 | $0-48 |
| LanguageTool Premium (cloud) | $4.99 | $59.88 |
Practical Recommendation
For a team currently paying for Grammarly Pro:
- Install LanguageTool self-hosted on a small VPS ($4/month)
- Configure browser extensions to point at your self-hosted instance
- Add Harper to developer editors for lightweight in-editor checking
- Set up Ollama for AI writing improvement tasks
Total cost: ~$4-8/month for the entire team. Compare to $1,800+/year for Grammarly Teams.
The main thing you lose: Grammarly's seamless browser integration and polished UI. LanguageTool's browser extension is functional but less polished. For teams where convenience matters more than cost, Grammarly's pricing may still be justified.
Find Your Writing Assistant
Browse all Grammarly alternatives on OSSAlt — compare LanguageTool, Harper, and every other open source writing and grammar tool with deployment guides and feature comparisons.