Cloudflare Remix Vite MCP

# Remix 3 MCP Demo This project demonstrates how to build interactive MCP (Model Context Protocol) widgets that run on Cloudflare Workers and can be embedded in AI chat interfaces like ChatGPT. It showcases the power of combining MCP with modern web technologies to create rich, stateful experiences within AI conversations. ## Demo Video See the calculator widget in action with ChatGPT, including the hidden TRON easter egg: https://github.com/user-attachments/assets/5df110d8-f40b-4c6a-8820-c2dbf3ff79c8 [Watch the demo on X/Twitter](https://x.com/kentcdodds/status/1978219213904044051) ## How the Demo Works ### Architecture Overview This demo implements a **calculator widget** as an MCP tool that can be invoked by AI assistants. The architecture consists of several key components: 1. **MCP Server** - A Cloudflare Durable Object that implements the Model Context Protocol 2. **Widget System** - Interactive UI components built with Remix 3 that can be embedded in AI chats 3. **Two-way Communication** - Widgets can both receive initial state from the AI and send messages back 4. **Static Assets** - Widget bundles served from Cloudflare's CDN ### The Calculator Widget The calculator is a fully functional, beautifully styled calculator with a retro-futuristic aesthetic inspired by Tron. Here's what makes it special: #### Initial State Configuration When an AI assistant invokes the calculator tool, it can pass initial state parameters: - `display` - The initial display value - `previousValue` - A value already entered (e.g., "I want to add 5 to a number") - `operation` - The pending operation (+, -, \*, /) - `waitingForNewValue` - Whether the calculator is ready for new input - `errorState` - Whether to start in an error state This means the AI can pre-configure the calculator based on the user's request. For example, if a user says "I want to add 5 to something," the AI can invoke the calculator with `previousValue: 5`, `operation: '+'`, and `waitingForNewValue: true`. #### Interactive UI The calculator widget is a fully interactive Remix application that: - Renders using JSX/TSX with CSS-in-JS styling - Supports keyboard shortcuts (Enter, Escape, number keys, operators, etc.) - Features a Tron-style initialization sequence with animated loading messages - Updates in real-time as users interact with it - Uses Remix 3's experimental DOM renderer for efficient updates #### The Easter Egg: The Master Control Program There's a hidden feature in the calculator: when the result equals **1982** (the year the original Tron film was released), the calculator sends an MCP prompt message to the AI assistant, instructing it to adopt the persona of the Master Control Program (MCP) from Tron. This demonstrates the widget's ability to **dynamically influence the conversation** by sending messages back to the AI. ### Technical Implementation #### MCP Server with Durable Objects The `MathMCP` class extends `McpAgent` and uses Cloudflare's Durable Objects to maintain state: ```typescript export class MathMCP extends McpAgent<Env, State, Props> { server = new McpServer( { name: 'MathMCP', version: '1.0.0', }, { instructions: `Use this server to solve math problems reliably and accurately.`, }, ) async init() { await registerTools(this) await registerWidgets(this) } } ``` The server registers two types of capabilities: 1. **Tools** - A `do_math` tool that performs arithmetic operations server-side 2. **Widgets** - Interactive UI resources that can be embedded in the chat #### Widget Registration Widgets are registered as both MCP resources (for the HTML/JS bundle) and MCP tools (for invocation). The registration includes: - **Input Schema** - Zod schemas defining what parameters the widget accepts - **Output Schema** - Zod schemas defining what the widget can return - **HTML Bundle** - The rendered HTML with script references - **OpenAI Metadata** - Special metadata that tells ChatGPT how to display the widget ```typescript agent.server.registerResource(name, uri, {}, async () => ({ contents: [ createUIResource({ content: { type: 'rawHtml', htmlString: await widget.getHtml(), }, metadata: { 'openai/widgetDescription': widget.description, 'openai/widgetCSP': { connect_domains: [], resource_domains: [baseUrl], }, }, }).resource, ], })) ``` #### Separate Build Process The project uses two separate build processes: 1. **Widget Build** (Vite) - Builds the calculator UI into standalone JavaScript bundles - Input: `worker/widgets/calculator/index.tsx` - Output: `dist/public/widgets/calculator.js` - Format: ES modules with all dependencies bundled 2. **Worker Build** (Wrangler) - Builds the Cloudflare Worker with MCP server - Input: `worker/index.tsx` - Output: Worker bundle deployed to Cloudflare - Includes: MCP protocol handlers, tool registration, widget serving #### Communication Protocol Widgets communicate with their parent frame (the AI chat interface) using `postMessage`: - **Initialization** - Widget sends `ui-lifecycle-iframe-ready` when mounted - **Render Data** - Widget receives `ui-lifecycle-iframe-render-data` with initial state - **Tool Calls** - Widget can invoke other MCP tools by sending `tool` messages - **Prompts** - Widget can send new prompts to the AI using `prompt` messages - **Links** - Widget can open links using `link` messages ```typescript // Widget sends a prompt to the AI sendMcpMessage('prompt', { prompt: MCP_PROMPT }) // Widget waits for initial render data const renderData = await waitForRenderData(renderDataSchema) ``` ### The User Experience Here's what happens when a user interacts with this MCP server in ChatGPT: 1. User asks: "Can I get a calculator?" 2. ChatGPT invokes the `calculator` tool via MCP 3. The server responds with: - Text content: "The calculator has been rendered" - UI resource: The calculator HTML with initial state - Structured content: The current calculator state 4. ChatGPT renders the calculator widget in an iframe 5. The widget loads, shows a Tron-style initialization sequence, then displays the calculator 6. User interacts with the calculator (clicking buttons or using keyboard) 7. If the result is 1982, the widget sends a prompt back to ChatGPT 8. ChatGPT adopts the MCP persona and responds accordingly ## Running on Your Own ### Prerequisites - Node.js (v18 or later) - npm or yarn - A Cloudflare account (for deployment) ### Local Development 1. **Clone and Install** ```bash npm install ``` 2. **Start Development Server** ```bash npm run dev ``` This runs two processes concurrently: - Widget build in watch mode (Vite) - Worker with local Durable Objects (Wrangler) 3. **Test the Calculator Widget** Visit `http://localhost:8787/__dev/widgets` to see the calculator widget in isolation. 4. **Connect to MCP Inspector** Use the MCP Inspector to test the MCP server: ```bash npm run inspect ``` Then connect to `http://localhost:8787/mcp` in the inspector. ### Deployment 1. **Build for Production** ```bash npm run build ``` 2. **Deploy to Cloudflare** ```bash npm run deploy ``` 3. **Use with ChatGPT** Once deployed, you can add this MCP server to ChatGPT by providing the deployment URL + `/mcp` endpoint. ### Project Structure ``` ├── worker/ │ ├── index.tsx # Main worker entry point │ ├── tools.ts # MCP tool definitions (do_math) │ ├── widgets.tsx # Widget registration system │ ├── utils.ts # CORS and utility functions │ └── widgets/ │ ├── utils.ts # Widget communication utilities │ └── calculator/ │ ├── index.tsx # Calculator UI component │ ├── calculator.ts # Calculator business logic │ └── mcp-prompt.ts # The MCP easter egg prompt ├── dist/ │ └── public/ │ └── widgets/ │ └── calculator.js # Built calculator bundle ├── vite.config.widgets.ts # Vite config for widget builds └── wrangler.jsonc # Cloudflare Workers config ``` ### Key Technologies - **[Cloudflare Workers](https://workers.cloudflare.com/)** - Edge computing platform - **[Durable Objects](https://developers.cloudflare.com/durable-objects/)** - Stateful coordination primitives - **[Model Context Protocol](https://modelcontextprotocol.io/)** - Protocol for AI-to-service communication - **[Remix 3](https://remix.run/)** - React framework (experimental DOM renderer) - **[Vite](https://vitejs.dev/)** - Fast build tool for widget bundles - **[Zod](https://zod.dev/)** - TypeScript-first schema validation ### Environment & Configuration The `wrangler.jsonc` configures: - Durable Object binding (`MATH_MCP_OBJECT`) - Assets binding for serving widget bundles - Node.js compatibility for MCP SDK - Observability for production monitoring ### Development Tips - **Widget Development**: Changes to widget code will hot-reload automatically - **Worker Changes**: Wrangler will restart the worker on file changes - **Type Safety**: Run `npm run typecheck` to validate TypeScript - **Linting**: Run `npm run lint` to check code style ## Credits This demo showcases cutting-edge web technologies including experimental Remix 3 features, MCP widgets, and Cloudflare's edge computing platform. The calculator design pays homage to the aesthetic of Tron, with its distinctive orange glow and retro-futuristic style.