PhysBox: MCP

PhysBox: MCP is a Model Context Protocol (MCP) server that enables LLMs and MCP clients (such as Claude Code or Claude Desktop) to interact programmatically with the three simulation web applications in the browser:

Application	Production URL	Description
Flux	flux.physbox.io	Discrete-event / system-dynamics simulation (interactive React Flow graph)
Volt	volt.physbox.io	SPICE circuit simulation (powered by NgSpice WASM in browser)
Mesh	mesh.physbox.io	Rigid-body physics simulation (powered by MuJoCo WASM in browser)

All communication is handled via JSON over WebSockets directly to the web app in your browser—no browser automation or DOM scraping is needed.

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How It Works

PhysBox: MCP functions as a local companion server that establishes a WebSocket relay on port 3142.

When you open any of the simulation web apps, they connect directly to this WebSocket relay. When an MCP client executes a tool call, the command flows from the client to the companion server, gets forwarded to the active browser tab, and the results flow back.

MCP Client (e.g. Claude Desktop)
  └── spawns → physbox-mcp (stdio)
                 └── WebSocket Server (ws://localhost:3142)
                                ├── Flux
                                ├── Volt
                                └── Mesh

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Installation

Install the companion server directly from PyPI:

pip install physbox-mcp

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Usage & Setup

1. Open the Web Applications

Launch or access the simulation web applications in your web browser:

• Flux: flux.physbox.io
• Volt: volt.physbox.io
• Mesh: mesh.physbox.io

As soon as a page finishes loading, it automatically registers with the companion WebSocket server.

2. Configure Your MCP Client

For Claude Desktop

Add the following block to your Claude Desktop configuration file (typically located at AppData/Roaming/Claude/claude_desktop_config.json on Windows or ~/Library/Application Support/Claude/claude_desktop_config.json on macOS):

{
  "mcpServers": {
    "physbox-mcp": {
      "command": "physbox-mcp",
      "args": ["--stdio"]
    }
  }
}

For Claude Code

Add a .mcp.json file to your project root (or update your global configuration at ~/.claude/mcp.json):

{
  "mcpServers": {
    "physbox-mcp": {
      "type": "stdio",
      "command": "physbox-mcp",
      "args": ["--stdio"]
    }
  }
}

3. Run the Companion Server Manually (Optional)

If you are running the server in HTTP mode rather than Stdio, you can run:

# Starts HTTP server listening on port 3141 (default)
physbox-mcp

Or configure custom port parameters:

physbox-mcp --port=4000

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Development & Contribution

For instructions on local development, modifying schemas, extending tool definitions, and manual builds, please refer to [README_DEV.md](file:///wsl.localhost/Ubuntu-20.04/home/boab/expt_mcp/README_DEV.md).