Antigravity Proxy

Intercept Google Antigravity IDE API calls and use your own Gemini API token

A MITM (Man-in-the-Middle) proxy that intercepts Google Antigravity IDE's API calls to generativelanguage.googleapis.com and replaces the authentication credentials with your own Gemini API token.

🎯 What This Does

Antigravity IDE → MITM Proxy → Google Gemini API
                    ↓
              [Replace API Key]
                    ↓
              Your API Token

• Intercepts all API calls from Antigravity to Google's Gemini API
• Replaces Google's API key with your own token
• Monitors all requests and responses for debugging
• Controls your own API usage and billing

⚡ Quick Start

# 1. Install dependencies
brew install mitmproxy
pip3 install python-dotenv

# 2. Setup SSL certificate
mitmproxy  # Press 'q' to quit
open ~/.mitmproxy/mitmproxy-ca-cert.pem
# In Keychain Access: Trust → "Always Trust"

# 3. Configure your API key
cp .env.example .env
# Edit .env and add your GEMINI_API_KEY

# 4. Start the proxy
mitmproxy -s mitmproxy-addon.py --listen-port 8080

# 5. Launch Antigravity (new terminal)
HTTP_PROXY=http://localhost:8080 \
HTTPS_PROXY=http://localhost:8080 \
/Applications/Antigravity.app/Contents/MacOS/Antigravity

📋 Prerequisites

• macOS (tested on macOS 14+, should work on Linux/Windows with minor adjustments)
• Python 3.8+
• Homebrew (for macOS)
• Google Gemini API Key (Get one free)

🚀 Installation

Step 1: Install mitmproxy

# macOS
brew install mitmproxy

# Linux (Ubuntu/Debian)
sudo apt install mitmproxy

# Or via pip
pip3 install mitmproxy

Step 2: Install Python Dependencies

pip3 install python-dotenv

Step 3: Install SSL Certificate

This step is critical for intercepting HTTPS traffic:

# Start mitmproxy to generate certificates
mitmproxy

Press q to quit. Certificate is now at ~/.mitmproxy/mitmproxy-ca-cert.pem

macOS:

# Open certificate in Keychain
open ~/.mitmproxy/mitmproxy-ca-cert.pem

1. Double-click "mitmproxy" certificate in Keychain Access
2. Expand "Trust" section
3. Set "When using this certificate" to "Always Trust"
4. Close (enter password when prompted)

Linux:

sudo cp ~/.mitmproxy/mitmproxy-ca-cert.pem /usr/local/share/ca-certificates/mitmproxy.crt
sudo update-ca-certificates

Windows:

# Open Certificate Manager
certmgr.msc
# Import ~/.mitmproxy/mitmproxy-ca-cert.pem to Trusted Root Certification Authorities

Step 4: Configure API Key

# Clone this repository
git clone https://github.com/yourusername/antigravity-proxy.git
cd antigravity-proxy

# Copy example config
cp .env.example .env

# Edit and add your API key
nano .env  # or use any editor

Set your Gemini API key:

GEMINI_API_KEY=your_actual_api_key_here

📖 Usage

Start the Proxy Server

cd antigravity-proxy

# Interactive mode (with TUI)
mitmproxy -s mitmproxy-addon.py --listen-port 8080

# Headless mode (terminal output only)
mitmdump -s mitmproxy-addon.py --listen-port 8080

# Web interface
mitmweb -s mitmproxy-addon.py --listen-port 8080
# Then open http://localhost:8081

Launch Antigravity with Proxy

Option 1: Using the launch script

./scripts/launch-antigravity.sh

Option 2: Manual launch

HTTP_PROXY=http://localhost:8080 \
HTTPS_PROXY=http://localhost:8080 \
/Applications/Antigravity.app/Contents/MacOS/Antigravity

Verify It's Working

When you use Antigravity's AI features, you should see in the proxy terminal:

📥 INCOMING REQUEST #1
   Method: POST
   URL: https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash:generateContent
   🔄 Replaced key in header
      Old: AIzaSyABC123***
      New: AIzaSyDEF456***

✅ RESPONSE
   Status: 200

📊 Stats: 1 requests, 1 keys replaced

🏗️ Architecture

This proxy uses mitmproxy, an industry-standard MITM proxy, with a custom Python addon (mitmproxy-addon.py) that:

1. Intercepts HTTPS requests to generativelanguage.googleapis.com
2. Extracts the original API key from headers or query parameters
3. Replaces it with your configured API key from .env
4. Forwards the modified request to Google's servers
5. Returns the response to Antigravity

Why mitmproxy?

• ✅ Industry-standard tool for API interception
• ✅ Handles SSL/TLS certificate generation automatically
• ✅ Can inspect and modify HTTPS traffic
• ✅ Well-documented and actively maintained
• ✅ Python scripting for custom logic

🔧 Configuration

Edit .env file:

# Your Google Gemini API Key (required)
GEMINI_API_KEY=your_api_key_here

# Proxy port (optional, default: 8080)
PROXY_PORT=8080

📚 Documentation

• MITMPROXY_SETUP.md - Complete setup guide
• IMPORTANT_NOTES.md - Technical limitations and alternatives
• docs/VSCODE_SETUP.md - VS Code configuration

🔒 Security Considerations

⚠️ IMPORTANT: This proxy is for local development only.

What this means:

• The mitmproxy certificate allows intercepting ALL HTTPS traffic
• Only use on your personal development machine
• Never use on production systems
• Don't expose the proxy to the internet
• Revoke certificate trust when done

API Key Security:

• Never commit .env to git (already in .gitignore)
• Don't share your .env file
• Use separate API keys for development/production
• Rotate keys regularly

See docs/SECURITY.md for detailed security information.

🐛 Troubleshooting

Certificate Not Trusted

Symptom: SSL/TLS errors in Antigravity

Solution:

1. Open Keychain Access (macOS)
2. Search for "mitmproxy"
3. Double-click certificate
4. Set Trust to "Always Trust"
5. Restart Antigravity

No Requests Appearing

Symptom: Proxy shows no traffic

Solutions:

1. Verify environment variables:

   echo $HTTP_PROXY
   echo $HTTPS_PROXY

2. Check proxy is running: lsof -ti:8080
3. Test with curl:

   HTTP_PROXY=http://localhost:8080 \
   HTTPS_PROXY=http://localhost:8080 \
   curl https://generativelanguage.googleapis.com/v1beta/models

API Key Not Replaced

Symptom: Proxy logs show no key replacement

Solution:

• Verify .env has correct GEMINI_API_KEY
• Check logs show "Replaced key in header"
• Ensure you copied .env.example to .env

See docs/TROUBLESHOOTING.md for more help.

🤝 Contributing

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

Development Setup

git clone https://github.com/yourusername/antigravity-proxy.git
cd antigravity-proxy
cp .env.example .env
# Edit .env with your API key

Running Tests

# Test the proxy with curl
HTTP_PROXY=http://localhost:8080 \
HTTPS_PROXY=http://localhost:8080 \
curl -v https://generativelanguage.googleapis.com/v1beta/models

📜 License

MIT License - see LICENSE file for details.

⚠️ Disclaimer

This tool is for educational and personal use only. Ensure you comply with:

• Google's Terms of Service
• Gemini API Terms of Service
• Gemini API Usage Policies
• Your organization's security policies

The authors are not responsible for any misuse or violations.

📦 Alternative Implementations

Node.js Experimental Branch

An educational Node.js implementation is available in the nodejs-experimental branch:

git checkout nodejs-experimental

Note: The Node.js version demonstrates proxy concepts but cannot inspect HTTPS content due to encryption limitations. Use the master branch (mitmproxy) for actual functionality.

See nodejs-experimental branch for details.

🙏 Acknowledgments

• mitmproxy - The excellent MITM proxy framework
• Google Antigravity team for building an interesting IDE
• Google Gemini team for the API

📞 Support

• Issues: GitHub Issues
• Documentation: See docs/ directory
• Security: See docs/SECURITY.md

🌟 Star This Project

If you find this project useful, please consider giving it a star ⭐

🗂️ Repository Structure

master (default)
├── mitmproxy-addon.py          # Working proxy solution
├── docs/                       # Documentation
├── scripts/                    # Helper scripts
└── README.md                   # This file

nodejs-experimental
├── src/                        # Node.js implementation (educational)
├── package.json               # Node.js dependencies
└── README_NODEJS.md           # Branch-specific docs

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Made with ❤️ for developers who want control over their AI API usage