OpenGrammar is the free, open-source Grammarly alternative. 40+ grammar rules run offline. Plug in your AI API key for advanced edits — no subscriptions, no data harvesting.
Built for developers, writers, and privacy advocates who want complete control over their writing tools.
No databases, no accounts, no tracking. The local engine runs fully offline. AI requests use a stateless edge function — text is never stored.
Paste your API key for OpenAI, Groq, OpenRouter, Together, or Ollama. Pay fractions of a cent — directly to the provider.
Deploy to Cloudflare Workers, Vercel Edge, Railway, Render, or Docker. One command. You own the infrastructure.
Offline checking for passive voice, repetition, spelling, punctuation, clichés, redundant phrases, double negatives, and more.
Rewrite text in 8 tones — Formal, Casual, Professional, Friendly, Concise, Detailed, Persuasive, and Neutral. Right-click or Ctrl+Shift+R.
Readability scores (Flesch, ARI), reading/speaking time, vocabulary diversity, and detailed analytics for every document.
Two engines work in parallel — fast local rules plus context-aware AI — then merge and rank results into a single clean list.
40+ regex rules run instantly in your browser. Passive voice, spelling, punctuation, clichés — all offline, all free.
For complex grammar and context-aware suggestions, text is sent to your chosen LLM via a stateless edge function.
Red, amber, and blue wavy underlines appear as you type. Click to apply, ignore, or add to your dictionary.
6 supported providers. From free to premium. From cloud to fully local.
Fastest inference with LPU technology. 100 free requests/day.
GPT-4o-mini for highest accuracy. ~$0.15/1K requests.
Run models on your own hardware. Complete privacy, works offline.
| Feature | Grammarly | OpenGrammar | LanguageTool |
|---|---|---|---|
| Price | $12/mo | Free | $4.99/mo |
| Open Source | Apache 2.0 | Partial | |
| Self-Hostable | Docker / CF Workers | ||
| Offline Mode | 40+ rules | Partial | |
| BYOK (Own AI Key) | 6 providers | ||
| Local LLM (Ollama) | |||
| Tone Rewriting | (Premium) | 8 tones | |
| Data Stored on Server | Yes | Stateless | Yes |
Clone, build, load. That's it.
# 1. Clone the repository git clone https://github.com/swadhinbiswas/opengrammar.git # 2. Build the extension cd opengrammar/opengrammar/extension bun install && bun run build # 3. Load in chrome://extensions → Load Unpacked → dist/ # 4. (Optional) Start local backend cd ../backend && bun run dev # Running at http://localhost:8787