A minimal and self-contained system for local preview environments.
Each app gets a unique subdomain URL, automatic hot reload, and live console capture — all without containers or sandboxes.

Modern online IDEs (like Sandpack, Lovable.dev, or Replit) are powerful but complex and heavy.
This system offers a lightweight alternative — built on Hono and standard Node.js — ideal for:

• Local development previews
• Multi-app testing
• AI coding agents that need ephemeral preview URLs

It’s not a sandbox. It’s a controlled iframe + proxy system for dev previews.

• 🌀 Subdomain-based routing → my-app.localhost:9100
• 🔥 Instant hot reload → Detects app reloads and updates iframes automatically
• 🪄 Console capture → See your app’s console.log() output in the parent frame
• 🔗 WebSocket proxying → Works seamlessly with Vite HMR
• 🧱 Multi-app management → Run multiple isolated apps at once
• 🧰 100% standalone → No Docker, no VMs, no external dependencies

# Install dependencies
npm install

# Start the server
npm run dev

Server starts at http://localhost:9100

mkdir apps/my-first-app
cd apps/my-first-app
npm init -y

Add an app (HTML or Vite):

# Simple HTML
echo '<h1>Hello World</h1>' > index.html
npx serve -p 9200

# or Vite app
npm create vite@latest . -- --template vanilla
npm install
npm run dev -- --port 9200

Now open: ➡️ http://my-first-app.localhost:9100

┌────────────────────────────────────────────┐
│ Hono Main Server (Port 9100)               │
│  - Subdomain routing                       │
│  - Proxy to app runtimes                   │
│  - Shim injection + console bridge         │
└──────────────────┬─────────────────────────┘
                   │
         ┌─────────┴──────────┐
         │                    │
┌────────▼────────┐   ┌───────▼────────┐
│ App Runtime     │   │ App Runtime    │
│ Port 9200       │   │ Port 9201      │
│ my-first-app    │   │ another-app    │
└─────────────────┘   └────────────────┘

Automatically injected into every HTML response:

• Captures console logs
• Sends them to the parent window (postMessage)
• Detects reloads and signals iframe refresh
• Manages iframe navigation (back/forward/reload)

1. App triggers reload (e.g. Vite HMR)
2. Shim detects beforeunload
3. Sends "will-reload" message to parent
4. Parent clears console logs + reloads iframe

.env example:

PORT=9100
RUNTIME_BASE_PORT=9200
NODE_ENV=development

src/server/constants.js (custom domains):

export const DOMAINS = ['yourdomain.com', 'localhost']

Simple and free-tier friendly.

1. Push your repo to GitHub
2. Create a Web Service on Render
3. Build Command → npm install
4. Start Command → npm start
5. Add environment variables
6. Deploy 🎉

Detailed steps in docs/render-deployment.md

npm test

Covers:

• Subdomain URL generation
• Proxy routing
• Shim injection
• Console message flow

Contributions are very welcome!

If you want to:

• Improve stability or add tests
• Enhance iframe–proxy communication
• Add integrations (e.g. R2, Cloudflare Workers)

Then feel free to:

1. Fork this repository
2. Create a new branch (feat/your-feature)
3. Open a pull request

Before submitting a PR, make sure all tests pass: npm test

MIT © 2025 César G. Leañez

Iframe Hot-Reload System — A minimal preview layer built with Hono for the next generation of AI coding agents.