Build an Interactive ChatGPT App

This guide will show you how to build and deploy an interactive ChatGPT App on Cloudflare Workers that can:

• Render rich, interactive UI widgets directly in ChatGPT conversations
• Maintain real-time, multi-user state using Durable Objects
• Enable bidirectional communication between your app and ChatGPT
• Build multiplayer experiences that run entirely within ChatGPT

You will build a real-time multiplayer chess game that demonstrates these capabilities. Players can start or join games, make moves on an interactive chessboard, and even ask ChatGPT for strategic adviceall without leaving the conversation.

Your ChatGPT App will use the Model Context Protocol (MCP) to expose tools and UI resources that ChatGPT can invoke on your behalf.

You can view the full code for this example here .

Before you begin, you will need:

• A Cloudflare account
• Node.js installed (v18 or later)
• A ChatGPT Plus or Team account with developer mode enabled
• Basic knowledge of React and TypeScript

To use ChatGPT Apps (also called connectors), you need to enable developer mode:

1. Open ChatGPT .
2. Go to Settings > Apps & Connectors > Advanced Settings
3. Toggle Developer mode ON

Once enabled, you will be able to install custom apps during development and testing.

1. Create a new project for your Chess App:

npm create cloudflare@latest -- my-chess-app

yarn create cloudflare my-chess-app

pnpm create cloudflare@latest my-chess-app

2. Navigate into your project:

cd my-chess-app

3. Install the required dependencies:

npm install agents @modelcontextprotocol/sdk chess.js react react-dom react-chessboard

4. Install development dependencies:

npm install -D @cloudflare/vite-plugin @vitejs/plugin-react vite vite-plugin-singlefile @types/react @types/react-dom

1. Update your wrangler.jsonc to configure Durable Objects and assets:

{
	"name": "my-chess-app",
	"main": "src/index.ts",
	// Set this to today's date
	"compatibility_date": "2026-08-19",
	"compatibility_flags": ["nodejs_compat"],
	"durable_objects": {
		"bindings": [
			{
				"name": "CHESS",
				"class_name": "ChessGame",
			},
		],
	},
	"migrations": [
		{
			"tag": "v1",
			"new_sqlite_classes": ["ChessGame"],
		},
	],
	"assets": {
		"directory": "dist",
		"binding": "ASSETS",
	},
}

name = "my-chess-app"
main = "src/index.ts"
# Set this to today's date
compatibility_date = "2026-08-19"
compatibility_flags = [ "nodejs_compat" ]

[[durable_objects.bindings]]
name = "CHESS"
class_name = "ChessGame"

[[migrations]]
tag = "v1"
new_sqlite_classes = [ "ChessGame" ]

[assets]
directory = "dist"
binding = "ASSETS"

2. Create a vite.config.ts for building your React UI:

import { cloudflare } from "@cloudflare/vite-plugin";
import react from "@vitejs/plugin-react";
import { defineConfig } from "vite";
import { viteSingleFile } from "vite-plugin-singlefile";

export default defineConfig({
	plugins: [react(), cloudflare(), viteSingleFile()],
	build: {
		minify: false,
	},
});

3. Update your package.json scripts:

{
	"scripts": {
		"dev": "vite",
		"build": "vite build",
		"deploy": "vite build && wrangler deploy"
	}
}

1. Create the game logic using Durable Objects at src/chess.tsx:

import { Agent, callable, getCurrentAgent } from "agents";
import { Chess } from "chess.js";

type Color = "w" | "b";

type ConnectionState = {
	playerId: string;
};

export type State = {
	board: string;
	players: { w?: string; b?: string };
	status: "waiting" | "active" | "mate" | "draw" | "resigned";
	winner?: Color;
	lastSan?: string;
};

export class ChessGame extends Agent<Env, State> {
	initialState: State = {
		board: new Chess().fen(),
		players: {},
		status: "waiting",
	};

	game = new Chess();

	constructor(
		ctx: DurableObjectState,
		public env: Env,
	) {
		super(ctx, env);
		this.game.load(this.state.board);
	}

	private colorOf(playerId: string): Color | undefined {
		const { players } = this.state;
		if (players.w === playerId) return "w";
		if (players.b === playerId) return "b";
		return undefined;
	}

	@callable()
	join(params: { playerId: string; preferred?: Color | "any" }) {
		const { playerId, preferred = "any" } = params;
		const { connection } = getCurrentAgent();
		if (!connection) throw new Error("Not connected");

		connection.setState({ playerId });
		const s = this.state;

		// Already seated? Return seat
		const already = this.colorOf(playerId);
		if (already) {
			return { ok: true, role: already as Color, state: s };
		}

		// Choose a seat
		const free: Color[] = (["w", "b"] as const).filter((c) => !s.players[c]);
		if (free.length === 0) {
			return { ok: true, role: "spectator" as const, state: s };
		}

		let seat: Color = free[0];
		if (preferred === "w" && free.includes("w")) seat = "w";
		if (preferred === "b" && free.includes("b")) seat = "b";

		s.players[seat] = playerId;
		s.status = s.players.w && s.players.b ? "active" : "waiting";
		this.setState(s);
		return { ok: true, role: seat, state: s };
	}

	@callable()
	move(
		move: { from: string; to: string; promotion?: string },
		expectedFen?: string,
	) {
		if (this.state.status === "waiting") {
			return {
				ok: false,
				reason: "not-in-game",
				fen: this.game.fen(),
				status: this.state.status,
			};
		}

		const { connection } = getCurrentAgent();
		if (!connection) throw new Error("Not connected");
		const { playerId } = connection.state as ConnectionState;

		const seat = this.colorOf(playerId);
		if (!seat) {
			return {
				ok: false,
				reason: "not-in-game",
				fen: this.game.fen(),
				status: this.state.status,
			};
		}

		if (seat !== this.game.turn()) {
			return {
				ok: false,
				reason: "not-your-turn",
				fen: this.game.fen(),
				status: this.state.status,
			};
		}

		// Optimistic sync guard
		if (expectedFen && expectedFen !== this.game.fen()) {
			return {
				ok: false,
				reason: "stale",
				fen: this.game.fen(),
				status: this.state.status,
			};
		}

		const res = this.game.move(move);
		if (!res) {
			return {
				ok: false,
				reason: "illegal",
				fen: this.game.fen(),
				status: this.state.status,
			};
		}

		const fen = this.game.fen();
		let status: State["status"] = "active";
		if (this.game.isCheckmate()) status = "mate";
		else if (this.game.isDraw()) status = "draw";

		this.setState({
			...this.state,
			board: fen,
			lastSan: res.san,
			status,
			winner:
				status === "mate" ? (this.game.turn() === "w" ? "b" : "w") : undefined,
		});

		return { ok: true, fen, san: res.san, status };
	}

	@callable()
	resign() {
		const { connection } = getCurrentAgent();
		if (!connection) throw new Error("Not connected");
		const { playerId } = connection.state as ConnectionState;

		const seat = this.colorOf(playerId);
		if (!seat) return { ok: false, reason: "not-in-game", state: this.state };

		const winner = seat === "w" ? "b" : "w";
		this.setState({ ...this.state, status: "resigned", winner });
		return { ok: true, state: this.state };
	}
}

1. Create your main worker at src/index.ts:

import { createMcpHandler } from "agents/mcp";
import { routeAgentRequest } from "agents";
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { env } from "cloudflare:workers";

const getWidgetHtml = async (host: string) => {
	let html = await (await env.ASSETS.fetch("http://localhost/")).text();
	html = html.replace(
		"<!--RUNTIME_CONFIG-->",
		`<script>window.HOST = \`${host}\`;</script>`,
	);
	return html;
};

function createServer() {
	const server = new McpServer({ name: "Chess", version: "v1.0.0" });

	// Register a UI resource that ChatGPT can render
	server.registerResource(
		"chess",
		"ui://widget/index.html",
		{},
		async (_uri, extra) => {
			return {
				contents: [
					{
						uri: "ui://widget/index.html",
						mimeType: "text/html+skybridge",
						text: await getWidgetHtml(
							extra.requestInfo?.headers.host as string,
						),
					},
				],
			};
		},
	);

	// Register a tool that ChatGPT can call to render the UI
	server.registerTool(
		"playChess",
		{
			title: "Renders a chess game menu, ready to start or join a game.",
			annotations: { readOnlyHint: true },
			_meta: {
				"openai/outputTemplate": "ui://widget/index.html",
				"openai/toolInvocation/invoking": "Opening chess widget",
				"openai/toolInvocation/invoked": "Chess widget opened",
			},
		},
		async (_, _extra) => {
			return {
				content: [
					{ type: "text", text: "Successfully rendered chess game menu" },
				],
			};
		},
	);

	return server;
}

export default {
	async fetch(req: Request, env: Env, ctx: ExecutionContext) {
		const url = new URL(req.url);
		if (url.pathname.startsWith("/mcp")) {
			// Create a new server instance per request
			const server = createServer();
			return createMcpHandler(server)(req, env, ctx);
		}

		return (
			(await routeAgentRequest(req, env)) ??
			new Response("Not found", { status: 404 })
		);
	},
} satisfies ExportedHandler<Env>;

export { ChessGame } from "./chess";

1. Create the HTML entry point at index.html:

<!doctype html>
<html>
	<head>
		<!--RUNTIME_CONFIG-->
	</head>
	<body>
		<div id="root" style="font-family: verdana"></div>
		<script type="module" src="/src/app.tsx"></script>
	</body>
</html>

2. Create the React app at src/app.tsx:

import { useEffect, useRef, useState } from "react";
import { useAgent } from "agents/react";
import { createRoot } from "react-dom/client";
import { Chess, type Square } from "chess.js";
import { Chessboard, type PieceDropHandlerArgs } from "react-chessboard";
import type { State as ServerState } from "./chess";

function usePlayerId() {
	const [pid] = useState(() => {
		const existing = localStorage.getItem("playerId");
		if (existing) return existing;
		const id = crypto.randomUUID();
		localStorage.setItem("playerId", id);
		return id;
	});
	return pid;
}

function App() {
	const playerId = usePlayerId();
	const [gameId, setGameId] = useState<string | null>(null);
	const [gameIdInput, setGameIdInput] = useState("");
	const [menuError, setMenuError] = useState<string | null>(null);

	const gameRef = useRef(new Chess());
	const [fen, setFen] = useState(gameRef.current.fen());
	const [myColor, setMyColor] = useState<"w" | "b" | "spectator">("spectator");
	const [pending, setPending] = useState(false);
	const [serverState, setServerState] = useState<ServerState | null>(null);
	const [joined, setJoined] = useState(false);

	const host = window.HOST ?? "http://localhost:5173/";

	const { stub } = useAgent<ServerState>({
		host,
		name: gameId ?? "__lobby__",
		agent: "chess",
		onStateUpdate: (s) => {
			if (!gameId) return;
			gameRef.current.load(s.board);
			setFen(s.board);
			setServerState(s);
		},
	});

	useEffect(() => {
		if (!gameId || joined) return;

		(async () => {
			try {
				const res = await stub.join({ playerId, preferred: "any" });
				if (!res?.ok) return;

				setMyColor(res.role);
				gameRef.current.load(res.state.board);
				setFen(res.state.board);
				setServerState(res.state);
				setJoined(true);
			} catch (error) {
				console.error("Failed to join game", error);
			}
		})();
	}, [playerId, gameId, stub, joined]);

	async function handleStartNewGame() {
		const newId = crypto.randomUUID();
		setGameId(newId);
		setGameIdInput(newId);
		setMenuError(null);
		setJoined(false);
	}

	async function handleJoinGame() {
		const trimmed = gameIdInput.trim();
		if (!trimmed) {
			setMenuError("Enter a game ID to join.");
			return;
		}
		setGameId(trimmed);
		setMenuError(null);
		setJoined(false);
	}

	const handleHelpClick = () => {
		window.openai?.sendFollowUpMessage?.({
			prompt: `Help me with my chess game. I am playing as ${myColor} and the board is: ${fen}. Please only offer written advice.`,
		});
	};

	function onPieceDrop({ sourceSquare, targetSquare }: PieceDropHandlerArgs) {
		if (!gameId || !sourceSquare || !targetSquare || pending) return false;

		const game = gameRef.current;
		if (myColor === "spectator" || game.turn() !== myColor) return false;

		const piece = game.get(sourceSquare as Square);
		if (!piece || piece.color !== myColor) return false;

		const prevFen = game.fen();

		try {
			const local = game.move({
				from: sourceSquare,
				to: targetSquare,
				promotion: "q",
			});
			if (!local) return false;
		} catch {
			return false;
		}

		const nextFen = game.fen();
		setFen(nextFen);
		setPending(true);

		stub
			.move({ from: sourceSquare, to: targetSquare, promotion: "q" }, prevFen)
			.then((r) => {
				if (!r.ok) {
					game.load(r.fen);
					setFen(r.fen);
				}
			})
			.finally(() => setPending(false));

		return true;
	}

	return (
		<div style={{ padding: "20px", background: "#f8fafc", minHeight: "100vh" }}>
			{!gameId ? (
				<div
					style={{
						maxWidth: "420px",
						margin: "0 auto",
						background: "#fff",
						borderRadius: "16px",
						padding: "24px",
					}}
				>
					<h1>Ready to play?</h1>
					<p>Start a new match or join an existing game.</p>
					<button
						onClick={handleStartNewGame}
						style={{
							padding: "12px",
							background: "#2563eb",
							color: "#fff",
							border: "none",
							borderRadius: "8px",
							cursor: "pointer",
							width: "100%",
						}}
					>
						Start a new game
					</button>
					<div style={{ marginTop: "16px" }}>
						<input
							placeholder="Paste a game ID"
							value={gameIdInput}
							onChange={(e) => setGameIdInput(e.target.value)}
							style={{
								width: "100%",
								padding: "10px",
								borderRadius: "8px",
								border: "1px solid #ccc",
							}}
						/>
						<button
							onClick={handleJoinGame}
							style={{
								marginTop: "8px",
								padding: "10px",
								background: "#0f172a",
								color: "#fff",
								border: "none",
								borderRadius: "8px",
								cursor: "pointer",
								width: "100%",
							}}
						>
							Join
						</button>
						{menuError && (
							<p style={{ color: "red", fontSize: "0.85rem" }}>{menuError}</p>
						)}
					</div>
				</div>
			) : (
				<div style={{ maxWidth: "600px", margin: "0 auto" }}>
					<div
						style={{
							background: "#fff",
							padding: "16px",
							borderRadius: "16px",
							marginBottom: "16px",
						}}
					>
						<h2>Game {gameId}</h2>
						<p>Status: {serverState?.status}</p>
						<button
							onClick={handleHelpClick}
							style={{
								padding: "10px",
								background: "#2563eb",
								color: "#fff",
								border: "none",
								borderRadius: "8px",
								cursor: "pointer",
							}}
						>
							Ask for help
						</button>
					</div>
					<div
						style={{
							background: "#fff",
							padding: "16px",
							borderRadius: "16px",
						}}
					>
						<Chessboard
							position={fen}
							onPieceDrop={onPieceDrop}
							boardOrientation={myColor === "b" ? "black" : "white"}
						/>
					</div>
				</div>
			)}
		</div>
	);
}

const root = createRoot(document.getElementById("root")!);
root.render(<App />);

1. Build your React UI:

npm run build

This compiles your React app into a single HTML file in the dist directory.

2. Deploy to Cloudflare:

npx wrangler deploy

After deployment, you will see your app URL:

https://my-chess-app.YOUR_SUBDOMAIN.workers.dev

Now connect your deployed app to ChatGPT:

1. Open ChatGPT .
2. Go to Settings > Apps & Connectors > Create
3. Give your app a name, and optionally a description and icon.
4. Enter your MCP endpoint: https://my-chess-app.YOUR_SUBDOMAIN.workers.dev/mcp.
5. Select "No authentication".
6. Select "Create".

Try it out:

1. In your ChatGPT conversation, type: "Let's play chess".
2. ChatGPT will call the playChess tool and render your interactive chess widget.
3. Select "Start a new game" to create a game.
4. Share the game ID with a friend who can join via their own ChatGPT conversation.
5. Make moves by dragging pieces on the board.
6. Select "Ask for help" to get strategic advice from ChatGPT

The Model Context Protocol (MCP) server defines tools and resources that ChatGPT can access. Note that we create a new server instance per request to prevent cross-client response leakage:

function createServer() {
	const server = new McpServer({ name: "Chess", version: "v1.0.0" });

	// Register a UI resource that ChatGPT can render
	server.registerResource(
		"chess",
		"ui://widget/index.html",
		{},
		async (_uri, extra) => {
			return {
				contents: [
					{
						uri: "ui://widget/index.html",
						mimeType: "text/html+skybridge",
						text: await getWidgetHtml(
							extra.requestInfo?.headers.host as string,
						),
					},
				],
			};
		},
	);

	// Register a tool that ChatGPT can call to render the UI
	server.registerTool(
		"playChess",
		{
			title: "Renders a chess game menu, ready to start or join a game.",
			annotations: { readOnlyHint: true },
			_meta: {
				"openai/outputTemplate": "ui://widget/index.html",
				"openai/toolInvocation/invoking": "Opening chess widget",
				"openai/toolInvocation/invoked": "Chess widget opened",
			},
		},
		async (_, _extra) => {
			return {
				content: [
					{ type: "text", text: "Successfully rendered chess game menu" },
				],
			};
		},
	);

	return server;
}

The ChessGame class extends Agent to create a stateful game engine:

export class ChessGame extends Agent<Env, State> {
  initialState: State = {
    board: new Chess().fen(),
    players: {},
    status: "waiting"
  };

  game = new Chess();

  constructor(
    ctx: DurableObjectState,
    public env: Env
  ) {
    super(ctx, env);
    this.game.load(this.state.board);
  }

Each game gets its own Agent instance, enabling:

• Isolated state per game
• Real-time synchronization across players
• Persistent storage that survives worker restarts

Use the @callable() decorator to expose methods that clients can invoke:

@callable()
join(params: { playerId: string; preferred?: Color | "any" }) {
  const { playerId, preferred = "any" } = params;
  const { connection } = getCurrentAgent();
  if (!connection) throw new Error("Not connected");

  connection.setState({ playerId });
  const s = this.state;

  // Already seated? Return seat
  const already = this.colorOf(playerId);
  if (already) {
    return { ok: true, role: already as Color, state: s };
  }

  // Choose a seat
  const free: Color[] = (["w", "b"] as const).filter((c) => !s.players[c]);
  if (free.length === 0) {
    return { ok: true, role: "spectator" as const, state: s };
  }

  let seat: Color = free[0];
  if (preferred === "w" && free.includes("w")) seat = "w";
  if (preferred === "b" && free.includes("b")) seat = "b";

  s.players[seat] = playerId;
  s.status = s.players.w && s.players.b ? "active" : "waiting";
  this.setState(s);
  return { ok: true, role: seat, state: s };
}

The useAgent hook connects your React app to the Durable Object:

const { stub } = useAgent<ServerState>({
	host,
	name: gameId ?? "__lobby__",
	agent: "chess",
	onStateUpdate: (s) => {
		gameRef.current.load(s.board);
		setFen(s.board);
		setServerState(s);
	},
});

Call methods on the agent:

const res = await stub.join({ playerId, preferred: "any" });
await stub.move({ from: "e2", to: "e4" });

Your app can send messages to ChatGPT:

const handleHelpClick = () => {
	window.openai?.sendFollowUpMessage?.({
		prompt: `Help me with my chess game. I am playing as ${myColor} and the board is: ${fen}. Please only offer written advice as there are no tools for you to use.`,
	});
};

This creates a new message in the ChatGPT conversation with context about the current game state.

Now that you have a working ChatGPT App, you can:

• Add more tools: Expose additional capabilities and UIs through MCP tools and resources.
• Enhance the UI: Build more sophisticated interfaces with React.

Agents API

Durable Objects

Model Context Protocol

OpenAI Apps SDK