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

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:

MCP Server - A Cloudflare Durable Object that implements the Model Context Protocol
Widget System - Interactive UI components built with Remix 3 that can be embedded in AI chats
Two-way Communication - Widgets can both receive initial state from the AI and send messages back
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:

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:

Tools - A do_math tool that performs arithmetic operations server-side
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

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:

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
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

// 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:

User asks: "Can I get a calculator?"
ChatGPT invokes the calculator tool via MCP
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
ChatGPT renders the calculator widget in an iframe
The widget loads, shows a Tron-style initialization sequence, then displays the calculator
User interacts with the calculator (clicking buttons or using keyboard)
If the result is 1982, the widget sends a prompt back to ChatGPT
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

Clone and Install
npm install
Start Development Server
npm run dev
This runs two processes concurrently:
- Widget build in watch mode (Vite)
- Worker with local Durable Objects (Wrangler)
Test the Calculator Widget
Visit http://localhost:8787/__dev/widgets to see the calculator widget in isolation.
Connect to MCP Inspector
Use the MCP Inspector to test the MCP server:
npm run inspect
Then connect to http://localhost:8787/mcp in the inspector.

Deployment

Build for Production
npm run build
Deploy to Cloudflare
npm run deploy
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 - Edge computing platform
Durable Objects - Stateful coordination primitives
Model Context Protocol - Protocol for AI-to-service communication
Remix 3 - React framework (experimental DOM renderer)
Vite - Fast build tool for widget bundles
Zod - 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.

This server cannot be installed

-

security - not tested

F

license - not found

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quality - not tested

How are these scores calculated?

remote-capable server

The server can be hosted and run remotely because it primarily relies on remote services or has no dependency on the local environment.

Enables interactive calculator widget functionality within AI chat interfaces, with the ability to perform math operations and dynamically influence conversations. Built on Cloudflare Workers with Remix 3, showcasing how to create rich, stateful MCP widgets that can be embedded in AI assistants like ChatGPT.

Cloudflare Remix Vite MCP