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Overview

The sunpeak dev command starts a local development server with a built-in simulator and MCP server, allowing you to develop and test your MCP Resources both locally and with hosts like ChatGPT. 
sunpeak dev

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Features

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Hot Module Reload (HMR)

The dev server uses Vite’s hot reload technology for instant feedback:
  • Component changes reflect immediately without full page refresh
  • State is preserved across updates when possible
  • CSS updates apply instantly
  • MCP server also supports HMR - no more cache issues or manual refreshes in ChatGPT

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Simulator

Access the simulator at http://localhost:3000 to:
  • Test your MCP Resources in a ChatGPT-like environment
  • Simulate tool calls and responses
  • Preview your UI components with realistic styling
  • Iterate quickly without needing a tunnel or ChatGPT connection

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MCP Server

The dev server also runs an MCP server on port 8000 for testing with hosts like ChatGPT:
  • Serves your apps to ChatGPT via MCP
  • Automatically rebuilds when you make changes
  • Uses unique URIs to cache-bust ChatGPT’s aggressive caching

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Automatic Discovery

The dev server automatically discovers and loads:
  • All resource folders from src/resources/{name}/
  • All simulations from tests/simulations/{name}/ ({name}-{scenario}-simulation.json)
No manual configuration or entry point files needed!

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Options

OptionShortDescription
--port <number>-pPort for the simulator (default: 3000, also respects PORT env var)
--prod-mcpServe production build .html files over MCP instead of Vite HMR (requires sunpeak build first)

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Configuration

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Ports

Default simulator port: 3000 Default MCP server port: 8000

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Usage

sunpeak dev
Or with a custom port: 
sunpeak dev --port 3000

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When to Use

Use sunpeak dev for:
  • Local component development with the simulator
  • Testing with real ChatGPT via the integrated MCP server
  • Rapid iteration with hot reload in either context
The dev server is for development only. For production, use sunpeak build to create optimized bundles.

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Connecting to ChatGPT

To test with the real ChatGPT, expose the MCP server with a tunnel: 
# In another terminal, run a tunnel
ngrok http 8000
Then connect the tunnel URL at the /mcp path (e.g., https://your-subdomain.ngrok.io/mcp) from ChatGPT in developer mode: User > Settings > Apps & Connectors > Create.

sunpeak build

Build production bundles