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:

1. Install LanguageTool self-hosted on a small VPS ($4/month)
2. Configure browser extensions to point at your self-hosted instance
3. Add Harper to developer editors for lightweight in-editor checking
4. 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.

Why Grammar Checking Matters Beyond Spelling

The case against Grammarly is often framed as a cost argument, but there is a more fundamental reason to consider privacy-respecting alternatives: Grammarly processes every word you type on any device where the extension is installed. That includes legal correspondence, salary negotiation emails, NDA drafts, customer support responses, and medical communications. The extension operates at the browser level and captures text before it is sent to any destination.

Grammarly's privacy policy states that they use aggregated, de-identified data for product improvement and research. For individual users, this may be acceptable. For organizations handling confidential client information, attorney-client privileged communications, or regulated personal data, allowing a third-party service to process that text is a compliance and confidentiality risk that often goes unexamined because "we just use Grammarly."

Self-hosted LanguageTool eliminates this risk entirely. Text is sent to your own server, processed locally in Java, and the results are returned to you. Nothing leaves your infrastructure. For law firms, healthcare organizations, financial services companies, and any business with confidentiality obligations, this distinction matters.

Choosing Between LanguageTool and AI Writing Assistance

LanguageTool and local AI writing assistance (via Ollama) solve different problems and are best used together rather than as alternatives to each other.

LanguageTool excels at deterministic, rule-based checking: subject-verb agreement, comma splice detection, commonly confused words (their/there/they're), passive voice overuse, and style consistency. These are things a capable grammar checker catches reliably with near-zero false negative rate. LanguageTool has been trained on linguistic rules for years, and for its coverage areas, it is genuinely reliable.

Local AI writing assistance is better for higher-level tasks: improving clarity and concision, adjusting tone (more formal, more conversational), restructuring a paragraph for better flow, or generating alternative phrasings for awkward sentences. Current models like Llama 3.1 8B and Qwen2.5 14B are good enough for these tasks that they compare favorably with Grammarly's AI-powered suggestions.

The practical workflow: run LanguageTool in your browser extension (pointing at your self-hosted instance) for continuous real-time grammar checking as you type, and use Ollama selectively for specific passages that need higher-level editing attention. This combination covers everything Grammarly does at a total infrastructure cost of about $4/month — less than a single Grammarly Pro seat.

For teams building out a complete open source stack, grammar and writing tools fit naturally alongside the analytics, project management, and communication tools covered elsewhere on OSSAlt. The complete business stack under $50/month guide shows how writing tools integrate into a broader self-hosted stack. And for the specific problem of evaluating open source tools for enterprise use — assessing security, licensing, and support options — the enterprise evaluation framework applies directly to LanguageTool and similar tools.

LanguageTool's deployment footprint is small enough to share a server with other services. The Docker image consumes approximately 1–2 GB of RAM depending on whether ngrams are loaded, and a Hetzner CX22 instance ($4.50/month) running LanguageTool alongside a few other lightweight tools costs less per month than a single Grammarly Pro seat. For teams with 10 or more users, the economics justify dedicated infrastructure within the first week of deployment. The annual savings at 10 users — $1,800/year for Grammarly Teams vs $54/year for a dedicated small VPS — are approximately the same as one month of a mid-level engineer's salary.

The browser extension configuration is worth repeating because it is the step most commonly skipped: after installing the LanguageTool browser extension, go to the extension settings and change the server URL from https://api.languagetoolplus.com to http://your-server:8010. Without this step, the extension continues sending text to LanguageTool's cloud servers even though you have a self-hosted instance running. Verify the connection by checking the extension's status indicator — it should show "Connected to custom server" rather than the default cloud connection.

Grammar and writing quality tools fit naturally alongside the other professional tools in a self-hosted stack. Teams running Mattermost for team communication and Outline for documentation — both covered in the complete business stack under $50/month guide — can route both tools' outbound text through the same self-hosted LanguageTool instance via browser extension. The LanguageTool extension works in text fields across the entire browser, so users get grammar checking in Mattermost message composition boxes, Outline editor, email clients, and every other web-based text input automatically once the extension is installed and configured.

For technical documentation specifically, Harper's editor integration provides grammar checking at the point of writing — in VS Code, Neovim, or Zed — before text ever reaches a web UI. Development teams that write documentation, commit messages, and code comments in their editors benefit from Harper running locally without any server infrastructure. Combining Harper for editor-level checking with a self-hosted LanguageTool instance for browser-based writing gives teams both layers of coverage without any per-user subscription cost. For the full evaluation framework for making open source tool adoption decisions, see how to evaluate open source alternatives.

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.