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ChatGPT app with Next.js

Ship a ChatGPT app on Vercel with Next.js and Model Context Protocol (MCP).

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chatgpt-apps

ChatGPT Apps SDK Next.js Starter

A minimal Next.js application demonstrating how to build an OpenAI Apps SDK compatible MCP server with widget rendering in ChatGPT.

Overview

This project shows how to integrate a Next.js application with the ChatGPT Apps SDK using the Model Context Protocol (MCP). It includes a working MCP server that exposes tools and resources that can be called from ChatGPT, with responses rendered natively in ChatGPT.

Key Components

1. MCP Server Route (app/mcp/route.ts)

The core MCP server implementation that exposes tools and resources to ChatGPT.

Key features:

  • Tool registration with OpenAI-specific metadata
  • Resource registration that serves HTML content for iframe rendering
  • Cross-linking between tools and resources via templateUri

OpenAI-specific metadata:

{
  "openai/outputTemplate": widget.templateUri,      // Links to resource
  "openai/toolInvocation/invoking": "Loading...",   // Loading state text
  "openai/toolInvocation/invoked": "Loaded",        // Completion state text
  "openai/widgetAccessible": false,                 // Widget visibility
  "openai/resultCanProduceWidget": true            // Enable widget rendering
}

Full configuration options: OpenAI Apps SDK MCP Documentation

2. Asset Configuration (next.config.ts)

Critical: Set assetPrefix to ensure /_next/ static assets are fetched from the correct origin:

const nextConfig: NextConfig = {
  assetPrefix: baseURL,  // Prevents 404s on /_next/ files in iframe
};

Without this, Next.js will attempt to load assets from the iframe's URL, causing 404 errors.

3. CORS Middleware (middleware.ts)

Handles browser OPTIONS preflight requests required for cross-origin RSC (React Server Components) fetching during client-side navigation:

export function middleware(request: NextRequest) {
  if (request.method === "OPTIONS") {
    // Return 204 with CORS headers
  }
  // Add CORS headers to all responses
}

4. SDK Bootstrap (app/layout.tsx)

The <NextChatSDKBootstrap> component patches browser APIs to work correctly within the ChatGPT iframe:

What it patches:

  • history.pushState / history.replaceState - Prevents full-origin URLs in history
  • window.fetch - Rewrites same-origin requests to use the correct base URL
  • <html> attribute observer - Prevents ChatGPT from modifying the root element

Required configuration:

<html lang="en" suppressHydrationWarning>
  <head>
    <NextChatSDKBootstrap baseUrl={baseURL} />
  </head>
  <body>{children}</body>
</html>

Note: suppressHydrationWarning is currently required because ChatGPT modifies the initial HTML before the Next.js app hydrates, causing hydration mismatches.

Getting Started

Installation

npm install
# or
pnpm install

Development

npm run dev
# or
pnpm dev

Open http://localhost:3000 to see the app.

Testing the MCP Server

The MCP server is available at:

http://localhost:3000/mcp

Connecting from ChatGPT

  1. Deploy your app to Vercel
  2. In ChatGPT, navigate to Settings → Connectors → Create and add your MCP server URL with the /mcp path (e.g., https://your-app.vercel.app/mcp)

Note: Connecting MCP servers to ChatGPT requires developer mode access. See the connection guide for setup instructions.

Project Structure

app/
├── mcp/
│   └── route.ts          # MCP server with tool/resource registration
├── layout.tsx            # Root layout with SDK bootstrap
├── page.tsx              # Homepage content
└── globals.css           # Global styles
middleware.ts             # CORS handling for RSC
next.config.ts            # Asset prefix configuration

How It Works

  1. Tool Invocation: ChatGPT calls a tool registered in app/mcp/route.ts
  2. Resource Reference: Tool response includes templateUri pointing to a registered resource
  3. Widget Rendering: ChatGPT fetches the resource HTML and renders it in an iframe
  4. Client Hydration: Next.js hydrates the app inside the iframe with patched APIs
  5. Navigation: Client-side navigation uses patched fetch to load RSC payloads

Learn More

Deployment

This project is designed to work seamlessly with Vercel deployment. The baseUrl.ts configuration automatically detects Vercel environment variables and sets the correct asset URLs.

The configuration automatically handles:

  • Production URLs via VERCEL_PROJECT_PRODUCTION_URL
  • Preview/branch URLs via VERCEL_BRANCH_URL
  • Asset prefixing for correct resource loading in iframes
GitHub Repovercel-labs/chatgpt-apps-sdk-nextjs-starter
Use Cases
StarterAI
Stack
Next.js

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