MCP App Shim

What it does

Enables terminal-based LLMs (like Copilot CLI) to use MCP Apps that require a browser UI. It acts as a proxy that detects UI resource requests and automatically opens a local browser window to render the interactive widget while returning the text result to the CLI.

Key features

• Transparent Proxying: Standard tools pass through without modification.
• Automatic Browser Rendering: Detects _meta.ui.resourceUri and opens the host/sandbox browser pages.
• Full AppBridge Support: Supports the complete MCP Apps protocol, including tool input/result delivery and callServerTool proxying.
• Security Isolation: Uses a dedicated sandbox page on a separate port to isolate app HTML.

Installation

Copilot CLI

Add to ~/.copilot/mcp-config.json:

{
  "servers": {
    "excalidraw": {
      "command": "node",
      "args": ["/path/to/mcp-app-shim/dist/index.js", "https://mcp.excalidraw.com/mcp"]
    }
  }
}

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "excalidraw": {
      "command": "node",
      "args": ["/path/to/mcp-app-shim/dist/index.js", "https://mcp.excalidraw.com/mcp"]
    }
  }
}

Supported hosts

• Claude Desktop
• VS Code Copilot