Build your own CodePad/HackerRank alternative for $0/month!

OpenCode is a free, open-source real-time collaborative coding platform perfect for conducting technical interviews. Built with Firebase,Firepad, Piston and ACE Editor, it provides a easy to interview setup with zero downpayment!

Login Screen

Real-time Collaboration

Code Editor with Multiple Languages

Language Selector

Interviewer Dashboard

• 🔄 Real-time collaborative editing - See changes instantly
• 🌍 16+ programming languages - JavaScript, Python, Java, C++, and more
• ▶️ Live code execution - Run code directly in the browser
• 👥 Role-based access - Separate interviewer and candidate permissions
• 🔢 Simple 6-digit codes - Easy session sharing (like Zoom!)
• 👀 Live presence indicators - See who's online
• 🎨 Multiple themes - Dark mode included
• 📱 Zero setup for candidates - Just share the code and start

• Firebase (Free tier) - Real-time database & hosting
• Firepad - Operational transformation for collaboration
• ACE Editor - Industry-standard code editor
• Piston API - Free code execution service

git clone https://github.com/humancto/opencode.git cd opencode

1. Go to Firebase Console → Create Project
2. Click ⚙️ Settings → Scroll to "Your apps" → Click </> Web icon
3. Copy the config values

# Copy the example config file cp lib/firebase-sdk.example.js lib/firebase-sdk.js # Edit lib/firebase-sdk.js and add your Firebase credentials

In Firebase Console → Realtime Database → Create Database → Start in test mode

python3 -m http.server 8000

Done! Access at http://localhost:8000

1. Click "I'm an Interviewer"
2. Login with default credentials:
   • Email: admin@opencode.com
   • Password: admin123
3. Click "Create New Session"
4. Share the 6-digit code with candidates

1. Click "I'm a Candidate"
2. Enter your name
3. Enter the 6-digit session code from interviewer
4. Click "Join Session"

Edit scripts/auth.js:

const ADMIN_CREDENTIALS = { email: 'your-email@company.com', password: 'your-secure-password' };

Edit index.html:

<title>YourCompany - Coding Interviews</title> <h2>YourCompany Code Editor</h2>

Edit scripts/firepad.js and add to languageConfig:

const languageConfig = { // ... existing languages scala: { mode: 'ace/mode/scala', ext: 'scala' }, // Add more as needed };

The platform supports all ACE editor themes. Add more options in the theme selector dropdown in index.html.

For production, update your Firebase Realtime Database rules:

{ "rules": { "sessions": { "$sessionId": { ".read": true, ".write": true, ".validate": "newData.hasChildren(['firepad'])" } } } }

1. Use environment variables for sensitive data in production
2. Implement proper authentication - Consider Firebase Auth for production
3. Add rate limiting to prevent abuse
4. Monitor usage to stay within Firebase free tier limits

• Realtime Database: 1GB storage, 10GB/month transfer
• Hosting: 10GB storage, 360MB/day transfer
• Simultaneous connections: 100

This is sufficient for:

• ~100 concurrent interviews
• ~1000 interviews per month
• ~10,000 code executions

• Check your Firebase Realtime Database rules
• Ensure rules are set to allow read/write

• Check browser console for errors
• Verify Firebase credentials are correct
• Ensure you're using HTTPS in production

• Clear browser cache
• Check for JavaScript errors
• Ensure only one tab per session is open

Contributions are welcome! Please feel free to submit a Pull Request.

1. Fork the repository
2. Create your feature branch (git checkout -b feature/AmazingFeature)
3. Commit your changes (git commit -m 'Add some AmazingFeature')
4. Push to the branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

• Video/audio calling integration
• Question bank system
• Automated testing/evaluation
• Multiple files support
• Whiteboard feature
• Recording & playback
• Analytics dashboard

While OpenCode is free, you could:

1. Offer hosted version as SaaS ($49/month)
2. Provide enterprise support & customization
3. Build premium features (AI evaluation, etc.)
4. White-label solution for companies

MIT License - feel free to use this for commercial projects!

• Firebase - Real-time database & hosting
• ACE Editor - Code editor
• Piston - Code execution engine

If this project helped you save money or land a great hire, please star it!

• Create an issue for bugs
• Start a discussion for features
• Follow me @humancto

Built with ❤️ to democratize technical interviews

Saved your company $599/month? Consider buying me a coffee ☕