Your privacy-first writing assistant powered by Chrome on-device AI
Features • Why Proofly • Installation • Contributing • Privacy
Proofly is a free, open-source Chrome extension that brings professional-grade writing assistance directly to your browser—without compromising your privacy. Unlike cloud-based alternatives like Grammarly, LanguageTool, or QuillBot, Proofly uses Chrome's Built-in AI APIs to proofread your writing entirely on-device. Your keystrokes never leave your machine.
Traditional writing assistants require sending your text to remote servers:
- ❌ Your private data travels across the internet
- ❌ Your writing is stored on company servers
- ❌ Requires constant internet connectivity
- ❌ Subject to data breaches and privacy violations
- ❌ Injects excessive UI to the sites you visit
- ❌ Expensive subscription fees
Proofly runs 100% locally on your device:
- ✅ Zero data transmission - Everything stays on your machine
- ✅ Complete privacy - No servers, no logs, no tracking
- ✅ Works offline - No internet required after model download
- ✅ Free forever - Open source, no subscriptions
- ✅ Lightweight - Minimal script injection, zero dependencies
- ✅ User friendly - Introduces fresh, non-invasive UX patterns
- ✅ Customizable - Complete control on how you'd like to get assistance
- On-Device Processing: All AI proofreading happens locally using Chrome's Built-in AI models
- Zero Server Communication: Your text never leaves your browser
- No Telemetry: We don't collect any usage data or analytics
- Open Source: Complete transparency - audit the code yourself
- Multilingual: Supports all languages that the built-in Gemini Nano model provides
- Spelling Corrections: Catch typos and misspellings instantly
- Grammar Fixes: Subject-verb agreement, tense consistency, and more
- Punctuation: Proper comma usage, missing periods, quotation marks
- Capitalization: Sentence starts, proper nouns, title case
- Preposition Usage: Correct preposition selection
- Missing Words: Detect incomplete sentences
- Visual Highlights: Color-coded underlines for different issue types
- Inline Corrections: Click any highlight to see suggestions
- Keyboard Shortcuts: Quick access with customizable hotkeys (Cmd/Ctrl+Shift+P)
- Auto-Correct Mode: Real-time checking as you type
- Manual Mode: Check on-demand whenever you want
- Selection Correction: Proofread your own highlighted text on-demand
- Issues Sidebar: View issues, navigate through them and apply suggested corrections in a dedicated panel
- Undo/Redo Support: Full history management for corrections
- Lightweight: Minimal footprint (<5KB initial injection)
- Fast: Instant suggestions powered by local on-device AI
- Shadow DOM Isolation: No interference with host pages
- Works Everywhere: Input fields, textareas, contenteditable elements
- Web Standards Compliant: Ignores auto-correction on fields based on their semantics
- Configurable Correction Types: Enable/disable specific issue types
- Custom Colors: Personalize highlight colors for each issue type
- Underline Styles: Choose solid, wavy, or dotted underlines
- Keyboard Shortcuts: Customize your workflow with auto-fix or manual-fix options
- Autofix on Double-Click: Quick correction with double-click
| Feature | Proofly | Grammarly | LanguageTool | QuillBot |
|---|---|---|---|---|
| Privacy | ✅ On-device only | ❌ Cloud-based | ❌ Cloud-based | ❌ Cloud-based |
| Works Offline | ✅ Yes | ❌ No | ❌ No | ❌ No |
| Cost | ✅ Free forever | 💰 $12-30/mo | 💰 $5-20/mo | 💰 $8-20/mo |
| Open Source | ✅ Yes | ❌ No | ❌ No | |
| No Data Collection | ✅ Zero tracking | ❌ Collects data | ❌ Collects data | ❌ Collects data |
| Lightweight | ✅ <5KB initial | ❌ Heavy scripts | ❌ Heavy scripts | ❌ Heavy scripts |
| Browser Support | Chrome 141+ | All browsers | All browsers | All browsers |
- Privacy You Can Verify: Open-source code means no hidden data collection
- No Subscription Treadmill: Free forever, no artificial limitations
- True Offline Mode: Works on airplanes, remote locations, anywhere
- Lightning Fast: No network latency, instant corrections
- Resource Efficient: Minimal CPU and memory usage
- Non-Invasive: Minimal native code is injected to the sites only when needed
- No Account Required: No sign-up, no email, no personal info
- Future-Proof: Uses Chrome's standard Built-in AI API and modern web tech
Proofly is built with modern web technologies and best practices:
- TypeScript - Strict type safety, comprehensive type coverage
- Web Components - Custom components - no framework bloat
- Chrome Built-in AI API - On-device proofreading and language detection models
- Web Components - Standards-compliant custom elements with Shadow DOM
- Vanilla JavaScript and CSS - Zero framework dependencies for minimal bundle size
- Functional Programming - Pure functions, composition, immutability
- Dependency Injection - Testable, modular service architecture
- Event-Driven Communication - Loosely coupled components
- Shadow DOM - Complete style isolation, no CSS conflicts
- CSS Custom Properties - Design token system for theming
- CSS Highlights API - Native browser highlighting for performance
- Popover API - Native popup positioning and management
- Chrome Storage API - Sync settings across devices
- Chrome Side Panel API - Dedicated sidebar interface
- Chrome Context Menus API - Right-click integration
- Content Scripts - Page interaction and highlighting
- Service Workers - Background processing
- TypeScript Compiler - Type checking and transpilation
- Vite Plugin Ecosystem - Build optimization and bundling
- Chrome Web Store Packaging - Automated release builds
- Hot Module Replacement - Instant dev feedback
- Operating System: Windows 10/11, macOS 13+, Linux, or ChromeOS (Chromebook Plus)
- Chrome Version: Chrome 141+
- Storage: At least 22 GB free space (for AI model download)
- GPU: Recommended 4+ GB VRAM for optimal performance
- Network: Internet connection for initial model download (one-time)
Proofly requires Chrome 141 or later with the Built-in AI Proofreader API enabled.
Note: The Proofreader API is in origin trial and will be available in stable Chrome soon.
- Visit the Chrome Web Store listing
- Click "Add to Chrome"
- Follow the on-screen setup
- Download the latest release from GitHub
- Extract the ZIP file
- Open Chrome and navigate to
chrome://extensions/ - Enable "Developer mode" (toggle in top-right)
- Click "Load unpacked"
- Select the extracted
dist/folder - Click on the Proofly icon and follow the setup wizard
# Clone the repository
git clone https://github.com/onderceylan/proofly.git
cd proofly
# Install dependencies
npm install
# Start development server with hot reload
npm run dev
# Build for production
# The extension will be built to dist/
npm run build
# Load dist/ as an unpacked extension in chrome://extensions/ for testing the prod build
# Load dev/ as an unpacked extension in chrome://extensions/ for testing the HMR dev build- Node.js 18+ and npm
- Chrome Canary or Chrome Dev
- Git
# Install dependencies
npm install
# Start development server (auto-rebuilds on changes)
npm run dev
# Build the project
npm run build
# Type checking
npm run typecheck
# Linting
npm run lint
# Format checking and fixing
npm run format:check
npm run format
# Unit tests
npm run test
npm run test:watch
# Puppeteer tests
npm run test:e2e
npm run test:e2e:watch
# For setting up e2e test env, load extension in Chrome once for your test-focused puppeteer user profile
# 1. Download https://www.google.com/chrome/dev/
# 2. Run `npm run test:e2e:watch` to open the browser profile of puppeteer or launch the browser manually with `/Applications/Google\ Chrome\ Dev.app/Contents/MacOS/Google\ Chrome\ Dev \ --user-data-dir=$HOME/.cache/chrome-devtools-mcp/chrome-profile-canary --load-extension=./projects/proofly/dev --no-first-run --hide-crash-restore-bubble`
# 3. Open chrome://extensions/
# 4. Enable "Developer mode"
# 5. Click "Load unpacked"
# 6. Select the dev folder
# 7. Download the AI model onceSee AGENTS.md for comprehensive development guidelines, including:
- Architecture principles
- Code style conventions
- Testing workflows
- Chrome extension patterns
- Logging guidelines
We welcome contributions from the community! Whether you're fixing bugs, adding features, or improving documentation, your help is appreciated.
- Pick an Issue: Browse open issues or propose new features
- Fork & Branch: Create a feature branch from
main - Make Changes: Follow our coding standards and conventions
- Test Thoroughly: Verify your changes work as expected through automated e2e tests
- Submit PR: Open a pull request with a clear description
- Privacy First: No data collection, no tracking, no telemetry
- Minimal Footprint: Keep bundle sizes small
- Long-term Maintenance: Avoid dependencies, and keep building on native web standards
- Non-Invasive: Respect the user's page and experience, keep injections minimal and isolated
- Accessibility: Support all users, including those with disabilities
- Performance: Optimize for speed and efficiency
- Zero Data Collection: We don't collect, store, or transmit any user data
- On-Device Processing: All AI runs locally on your machine
- No Analytics: No telemetry, no usage tracking, no crash reports
- No Accounts: No sign-up, no user profiles, no personal information
- Open Source: Fully auditable codebase for transparency
- Minimal Permissions: Only requests essential Chrome APIs
- Content Security Policy: Strict CSP prevents code injection
- Shadow DOM Isolation: UI components that are injected to the sites are completely isolated
- No External Resources: All assets bundled with extension
- Regular Security Audits: Community-driven code reviews
Read our full Privacy Policy for more details.
This project is licensed under the MIT License - see the LICENSE file for details.
- Chrome Team - For developing the Built-in AI API and making on-device AI accessible
- Open Source Community - For the amazing tools and libraries that make this possible
- Contributors - Everyone who helps improve Proofly
- Users - For trusting us with your privacy and writing
- Documentation: AGENTS.md
- Privacy Policy: PRIVACY.md
- Chrome Built-in AI: developer.chrome.com/docs/ai/built-in-apis
- Issue Tracker: GitHub Issues
- Discussions: GitHub Discussions
- Bug Reports: Open an issue
- Feature Requests: Request a feature
- Questions: Start a discussion
If you find Proofly useful, please consider:
- ⭐ Starring the repo
- 🐛 Reporting bugs
- 💡 Suggesting features
- 🔀 Contributing code
- 📢 Spreading the word
Privacy-first writing assistance is possible. Let's prove it together.