OpenGrammar is a free, privacy-first browser extension that gives you Grammarly-like writing help everywhere (Gmail, Google Docs, Notion, Reddit, etc.) without sending your data anywhere. Key points: • Core engine runs 100% locally in your browser (rule-based detection of passive voice, repetition, long sentences, readability). No internet needed. • Optional AI power: just paste your own OpenAI/Groq/OpenRouter/Ollama key. You pay only pennies for what you use. Your key never leaves the browser. • Tone rewriting (Formal, Casual, Professional, etc.) with one right-click. • Writing stats dashboard (Flesch score, reading time, vocabulary diversity). • Underlines suggestions in red/yellow/blue — click to apply. • Fully self-hostable backend (Cloudflare Workers or Vercel, one-command deploy).

I built this because I was tired of Grammarly storing everything I write and charging $30/month. Everything is open source (Apache 2.0), no accounts, no telemetry.

Demo video & screenshots coming soon. Right now you can try it in 2 minutes: 1. Clone the repo 2. Load the unpacked extension (chrome://extensions) 3. (Optional) add your API key

GitHub: https://github.com/swadhinbiswas/opengrammar

Would love feedback from writers, developers, and privacy enthusiasts. What grammar rules should I add next? Any features you miss from Grammarly?

(Also happy to take PRs — especially for more local rules!)