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😡 The Problem

"Opus 4.6 API costs hundreds per month" "Gemini 3.1 Pro is free but has no convenient API" "I want my agent to use multiple models without paying for each"

Antigravity Bridge wraps Antigravity — a free AI desktop app by Google — into a standard REST API via Chrome DevTools Protocol (CDP). One endpoint, six free models.

🚀 Quick Start

1. Install & Start

# Install Antigravity from https://antigravity.com (macOS only)

# Clone this repo
git clone https://github.com/ythx-101/antigravity-bridge.git
cd antigravity-bridge

# Install dependency
pip install websockets

# Start Antigravity with CDP
bash scripts/start_antigravity.sh

# Start the bridge
python3 scripts/bridge.py

2. Use the API

# Chat with Opus (free!)
curl -X POST http://localhost:19999/chat \
  -H 'Content-Type: application/json' \
  -d '{"prompt":"Explain quantum computing","model":"Claude Opus 4.6 (Thinking)"}'

# Async mode (recommended for long tasks)
curl -X POST http://localhost:19999/async \
  -d '{"prompt":"Deep analysis...","timeout":600}'
# → {"status":"accepted","task_id":"abc123"}
curl http://localhost:19999/task/abc123

# New conversation (clear context)
curl -X POST http://localhost:19999/new

# Health check
curl http://localhost:19999/health

🤖 Available Models

Model	Key	Best For
Claude Opus 4.6 (Thinking)	Claude Opus 4.6 (Thinking)	Deep reasoning
Gemini 3.1 Pro (High)	Gemini 3.1 Pro (High)	Fast + image gen
Claude Sonnet 4.6 (Thinking)	Claude Sonnet 4.6 (Thinking)	Balanced
Gemini 3 Flash	Gemini 3 Flash	Fastest
GPT-OSS 120B (Medium)	GPT-OSS 120B (Medium)	GPT alternative
Gemini 3.1 Pro (Low)	Gemini 3.1 Pro (Low)	Quota-friendly

📡 API Reference

Method	Path	Description
POST	/chat	Synchronous chat (default 180s timeout)
POST	/async	Async chat, returns task_id
GET	/task/{id}	Poll async result
POST	/new	New conversation (two-phase reload)
POST	/model	Switch model
GET	/health	Health check
GET	/models	List available models
GET	/history	Current conversation content
GET	/imgcount	Count generated images
GET	/extract?after=N	Extract generated image as base64

📊 Architecture

Your Agent / Script
    │
    ├── curl http://localhost:19999/chat
    │
    └── bridge.py (:19999)
          │ WebSocket (CDP)
          ▼
        Antigravity (CDP :9229)
          │ Security.setIgnoreCertificateErrors ← v1.3.0 fix
          ▼
        language_server_macos_arm
          │ gRPC over TLS
          ▼
        googleapis.com (AI models)

🔧 How It Works

1. Antigravity runs with --remote-debugging-port=9229 (auto-configured via argv.json)
2. bridge.py connects via CDP WebSocket to the Antigravity chat UI
3. Messages are injected into the Lexical editor via document.execCommand('insertText')
4. Responses are polled from the DOM until completion markers appear
5. SSL Fix: Antigravity's language_server uses a self-signed cert (CN=localhost). The bridge calls Security.setIgnoreCertificateErrors to allow the renderer's fetch() to communicate with it

⚠️ Known Issues & Solutions

"Messages send but no response" (most common)

Root cause: Electron's fetch() rejects the self-signed SSL cert used by language_server_macos_arm.

Fix (applied in v1.3.0): The bridge automatically calls Security.setIgnoreCertificateErrors({ignore: true}) before each chat.

"gRPC connection fails"

The language_server connects to daily-cloudcode-pa.googleapis.com via gRPC. If this endpoint is unreachable (e.g., blocked by firewall), models will show as placeholders and won't respond.

Fix: Ensure your network can reach googleapis.com.

Planning mode gets stuck

Some long prompts trigger Antigravity's "Planning" mode which can hang.

Fix: The bridge auto-switches to "Fast" mode. Keep prompts concise.

📁 Files

antigravity-bridge/
├── README.md
├── CHANGELOG.md
├── LICENSE
├── SKILL.md
└── scripts/
    ├── bridge.py             # REST API server (v1.3.0)
    └── start_antigravity.sh  # Mac startup helper

📝 Requirements

• macOS with Antigravity installed
• Python 3.8+ with websockets package
• Network access to googleapis.com

License

MIT