chatgpt-app-builder

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Build ChatGPT apps with interactive widgets using mcp-use and OpenAI Apps SDK. Use when creating ChatGPT apps, building MCP servers with widgets, defining React widgets, working with Apps SDK, or when user mentions ChatGPT widgets, mcp-use widgets, or Apps SDK development.

diegosouzapw By diegosouzapw schedule Updated 3/1/2026
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name: chatgpt-app-builder description: Build ChatGPT apps with interactive widgets using mcp-use and OpenAI Apps SDK. Use when creating ChatGPT apps, building MCP servers with widgets, defining React widgets, working with Apps SDK, or when user mentions ChatGPT widgets, mcp-use widgets, or Apps SDK development.

ChatGPT App Builder

Build production-ready ChatGPT apps with interactive widgets using mcp-use. Zero-config widget development with automatic registration and built-in React hooks.

Quick Start

npx create-mcp-use-app my-chatgpt-app --template mcp-apps
cd my-chatgpt-app
npm install && npm run dev

Project structure:

my-chatgpt-app/
├── resources/              # React widgets (auto-registered!)
│   ├── weather-display.tsx # Example widget
│   └── product-card.tsx    # Another widget
├── public/                 # Static assets
│   └── images/
├── index.ts               # MCP server entry
├── package.json
└── tsconfig.json

Why mcp-use for ChatGPT Apps?

Traditional OpenAI Apps SDK requires significant manual setup:

  • Separate project structure (server/ and web/ folders)
  • Manual esbuild/webpack configuration
  • Custom useWidgetState hook implementation
  • Manual React mounting code
  • Manual CSP configuration
  • Manual widget registration

mcp-use simplifies everything:

  • Single command setup
  • Drop widgets in resources/ folder - auto-registered
  • Built-in useWidget() hook with state, props, tool calls
  • Automatic bundling with hot reload
  • Automatic CSP configuration
  • Built-in Inspector for testing
  • Dual-protocol support (works with ChatGPT AND MCP Apps clients)

MCP Apps vs ChatGPT Apps SDK

Protocol Use Case Compatibility Status
MCP Apps (type: "mcpApps") Maximum compatibility ChatGPT + MCP Apps clients Recommended
ChatGPT Apps SDK (type: "appsSdk") ChatGPT-only features ChatGPT only Supported

Why MCP Apps? It's the official standard (SEP-1865) for interactive widgets:

  • Universal: Works with ChatGPT, Claude Desktop, Goose, and all MCP Apps clients
  • Future-proof: Based on open specification
  • Zero config: With type: "mcpApps", mcp-use generates metadata for BOTH protocols automatically

Creating Widgets

Simple Widget (Single File)

Create resources/weather-display.tsx:

import { McpUseProvider, useWidget, type WidgetMetadata } from "mcp-use/react";
import { z } from "zod";

export const widgetMetadata: WidgetMetadata = {
  description: "Display current weather for a city",
  props: z.object({
    city: z.string().describe("City name"),
    temperature: z.number().describe("Temperature in Celsius"),
    conditions: z.string().describe("Weather conditions"),
    humidity: z.number().describe("Humidity percentage"),
  }),
};

const WeatherDisplay: React.FC = () => {
  const { props, isPending } = useWidget();

  if (isPending) {
    return (
      <McpUseProvider autoSize>
        <div className="animate-pulse p-4">Loading weather...</div>
      </McpUseProvider>
    );
  }

  return (
    <McpUseProvider autoSize>
      <div className="weather-card p-4 rounded-lg shadow">
        <h2 className="text-2xl font-bold">{props.city}</h2>
        <div className="temp text-4xl">{props.temperature}°C</div>
        <p className="conditions">{props.conditions}</p>
        <p className="humidity">Humidity: {props.humidity}%</p>
      </div>
    </McpUseProvider>
  );
};

export default WeatherDisplay;

Widget is automatically:

  • Registered as MCP tool weather-display
  • Registered as MCP resource ui://widget/weather-display.html
  • Bundled for Apps SDK compatibility

Complex Widget (Folder Structure)

For widgets with multiple components:

resources/
└── product-search/
    ├── widget.tsx          # Entry point (required name)
    ├── components/
    │   ├── ProductCard.tsx
    │   └── FilterBar.tsx
    ├── hooks/
    │   └── useFilter.ts
    └── types.ts

Entry point must be named widget.tsx and export widgetMetadata + default component.

Widget Metadata

export const widgetMetadata: WidgetMetadata = {
  // Required: Human-readable description
  description: "Display weather information",

  // Required: Zod schema for widget props
  props: z.object({
    city: z.string().describe("City name"),
    temperature: z.number(),
  }),

  // Optional: Disable automatic tool registration
  exposeAsTool: true, // default

  // Optional: Unified metadata (works for BOTH ChatGPT and MCP Apps)
  metadata: {
    csp: {
      connectDomains: ["https://api.weather.com"],
      resourceDomains: ["https://cdn.weather.com"],
    },
    prefersBorder: true,
    autoResize: true,
    widgetDescription: "Interactive weather display",
  },
};

Key fields:

  • description: Used for tool and resource descriptions
  • props: Zod schema defines widget input parameters
  • exposeAsTool: Set to false if only using widget via custom tools
  • metadata: Unified configuration for both protocols (recommended)

Content Security Policy (CSP)

Control external resources your widget can access:

export const widgetMetadata: WidgetMetadata = {
  description: "Weather widget",
  props: z.object({ city: z.string() }),
  metadata: {
    csp: {
      // APIs to call (fetch, WebSocket, XMLHttpRequest)
      connectDomains: ["https://api.weather.com", "https://backup.weather.com"],
      // Static assets (images, fonts, stylesheets)
      resourceDomains: ["https://cdn.weather.com"],
      // External iframes
      frameDomains: ["https://embed.weather.com"],
      // Script directives (use carefully!)
      scriptDirectives: ["'unsafe-inline'"],
    },
  },
};

Security tips:

  • Specify exact domains: https://api.weather.com
  • Avoid wildcards in production
  • Never use 'unsafe-eval' unless necessary

For detailed CSP configuration and legacy format, see references/csp-and-metadata.md.

useWidget Hook

const {
  props,              // Widget input from tool (empty {} while pending)
  isPending,          // True while tool still executing
  state,              // Persistent widget state
  setState,           // Update persistent state
  theme,              // 'light' | 'dark' from host
  callTool,           // Call other MCP tools
  displayMode,        // 'inline' | 'pip' | 'fullscreen'
  requestDisplayMode, // Request display mode change
  output,             // Additional tool output
} = useWidget<MyPropsType, MyOutputType>();

Props and Loading States

Critical: Widgets render BEFORE tool execution completes. Always handle isPending:

const { props, isPending } = useWidget<WeatherProps>();

// Pattern 1: Early return
if (isPending) {
  return <div>Loading...</div>;
}
// Now props are safe to use

// Pattern 2: Conditional rendering
return (
  <div>
    {isPending ? <LoadingSpinner /> : <div>{props.city}</div>}
  </div>
);

// Pattern 3: Optional chaining (partial UI)
return (
  <div>
    <h1>{props.city ?? "Loading..."}</h1>
  </div>
);

Widget State

Persist data across widget interactions:

const { state, setState } = useWidget();

// Save state (persists in ChatGPT localStorage)
const addFavorite = async (city: string) => {
  await setState({
    favorites: [...(state?.favorites || []), city],
  });
};

// Update with function
await setState((prev) => ({
  ...prev,
  count: (prev?.count || 0) + 1,
}));

Calling MCP Tools

Widgets can call other tools:

const { callTool } = useWidget();

const refreshData = async () => {
  try {
    const result = await callTool("get-weather", { city: "Tokyo" });
    console.log("Result:", result.content);
  } catch (error) {
    console.error("Tool call failed:", error);
  }
};

Display Mode Control

const { displayMode, requestDisplayMode } = useWidget();

const goFullscreen = async () => {
  await requestDisplayMode("fullscreen");
};

// Current mode: 'inline' | 'pip' | 'fullscreen'
console.log(displayMode);

Custom Tools with Widgets

Create tools that return widgets:

import { MCPServer, widget, text } from "mcp-use/server";
import { z } from "zod";

const server = new MCPServer({
  name: "weather-app",
  version: "1.0.0",
  baseUrl: process.env.MCP_URL || "http://localhost:3000",
});

server.tool(
  {
    name: "get-weather",
    description: "Get current weather for a city",
    schema: z.object({
      city: z.string().describe("City name"),
    }),
    // Widget config (registration-time metadata)
    widget: {
      name: "weather-display", // Must match widget in resources/
      invoking: "Fetching weather...",
      invoked: "Weather data loaded",
    },
  },
  async ({ city }) => {
    const data = await fetchWeatherAPI(city);

    return widget({
      props: {
        city,
        temperature: data.temp,
        conditions: data.conditions,
        humidity: data.humidity,
      },
      output: text(`Weather in ${city}: ${data.temp}°C`),
      message: `Current weather for ${city}`,
    });
  }
);

server.listen();

Key points:

  • baseUrl in server config enables proper asset loading
  • widget: { name, invoking, invoked } on tool definition
  • widget({ props, output }) helper returns runtime data
  • props passed to widget, output shown to model

Static Assets

Use public/ folder for images, fonts:

my-app/
├── resources/
├── public/
│   ├── images/
│   │   ├── logo.svg
│   │   └── banner.png
│   └── fonts/
└── index.ts

Using assets in widgets:

import { Image } from "mcp-use/react";

function MyWidget() {
  return (
    <div>
      {/* Paths relative to public/ folder */}
      <Image src="/images/logo.svg" alt="Logo" />
      <img src={window.__getFile?.("images/banner.png")} alt="Banner" />
    </div>
  );
}

Components

McpUseProvider

Unified provider combining all common setup:

import { McpUseProvider } from "mcp-use/react";

function MyWidget() {
  return (
    <McpUseProvider
      autoSize      // Auto-resize widget
      viewControls  // Add debug/fullscreen buttons
      debug         // Show debug info
    >
      <div>Widget content</div>
    </McpUseProvider>
  );
}

Image Component

Handles both data URLs and public paths:

import { Image } from "mcp-use/react";

<Image src="/images/photo.jpg" alt="Photo" />
<Image src="data:image/png;base64,..." alt="Data URL" />

ErrorBoundary

import { ErrorBoundary } from "mcp-use/react";

<ErrorBoundary
  fallback={<div>Something went wrong</div>}
  onError={(error) => console.error(error)}
>
  <MyComponent />
</ErrorBoundary>

For full component API, see references/components-api.md.

Testing

Using the Inspector

  1. Start development: npm run dev
  2. Open http://localhost:3000/inspector
  3. Click Tools tab → Find your widget → Enter parameters → Execute
  4. Debug with browser console, RPC logs, state inspection

Testing in ChatGPT

  1. Enable Developer Mode: Settings → Connectors → Advanced → Developer mode
  2. Add your server: Connectors tab → Add remote MCP server URL
  3. Test: Select Developer Mode from Plus menu → Choose connector → Use tools

Prompting tips:

  • Be explicit: "Use the weather-app connector's get-weather tool..."
  • Disallow alternatives: "Do not use built-in tools, only use my connector"
  • Specify input: "Call get-weather with { city: 'Tokyo' }"

Dual-protocol note: With type: "mcpApps", widgets work in both ChatGPT and MCP Apps clients without code changes.

Best Practices

Schema Design

// Good - descriptive
const schema = z.object({
  city: z.string().describe("City name (e.g., Tokyo, Paris)"),
  temperature: z.number().min(-50).max(60).describe("Temp in Celsius"),
});

// Bad - no descriptions
const schema = z.object({
  city: z.string(),
  temp: z.number(),
});

Theme Support

const { theme } = useWidget();
const bgColor = theme === "dark" ? "bg-gray-900" : "bg-white";
const textColor = theme === "dark" ? "text-white" : "text-gray-900";

Loading States

Always check isPending first:

const { props, isPending } = useWidget<MyProps>();

if (isPending) return <LoadingSpinner />;
return <div>{props.field}</div>;

Widget Focus

Keep widgets focused on one thing:

// Good: Single purpose
export const widgetMetadata: WidgetMetadata = {
  description: "Display weather for a city",
  props: z.object({ city: z.string() }),
};

// Bad: Too many responsibilities
export const widgetMetadata: WidgetMetadata = {
  description: "Weather, forecast, map, news, and more",
  props: z.object({ /* many fields */ }),
};

Error Handling

const { callTool } = useWidget();

const fetchData = async () => {
  try {
    const result = await callTool("fetch-data", { id: "123" });
    if (result.isError) {
      console.error("Tool returned error");
    }
  } catch (error) {
    console.error("Tool call failed:", error);
  }
};

Configuration

Production Setup

const server = new MCPServer({
  name: "my-app",
  version: "1.0.0",
  baseUrl: process.env.MCP_URL || "https://myserver.com",
});

Environment Variables

MCP_URL=https://myserver.com
MCP_SERVER_URL=https://myserver.com/api
CSP_URLS=https://cdn.example.com,https://api.example.com

Deployment

npx mcp-use login
npm run deploy

Build for production:

npm run build
npm start

Troubleshooting

Widget Not Appearing

  • Ensure .tsx extension
  • Export widgetMetadata object
  • Export default React component
  • Check server logs for errors
  • Verify widget name matches file/folder name

Props Not Received

  • Check isPending first (props empty while pending)
  • Use useWidget() hook (not React props)
  • Verify widgetMetadata.props is valid Zod schema
  • Check tool parameters match schema

CSP Errors

  • Set baseUrl in server config
  • Add domains to CSP via metadata.csp
  • Use HTTPS for all resources
  • Check browser console for CSP violations

Protocol Compatibility

  • Use type: "mcpApps" for dual-protocol support
  • Set baseUrl correctly in server config
  • Use metadata (camelCase) not appsSdkMetadata for dual-protocol
  • Test in Inspector which supports both protocols

Quick Reference

Commands:

  • npx create-mcp-use-app my-app --template mcp-apps - Bootstrap
  • npm run dev - Development with hot reload
  • npm run build - Build for production
  • npm start - Run production server
  • npm run deploy - Deploy to mcp-use Cloud

Widget structure:

  • resources/widget-name.tsx - Single file widget
  • resources/widget-name/widget.tsx - Folder-based widget entry
  • public/ - Static assets

Widget metadata:

  • description - Widget description (required)
  • props - Zod schema for input (required)
  • exposeAsTool - Auto-register as tool (default: true)
  • metadata - Unified config (dual-protocol)
  • metadata.csp - Content Security Policy

useWidget returns:

  • props - Widget input parameters
  • isPending - Loading state flag
  • state, setState - Persistent state
  • callTool - Call other tools
  • theme - Current theme (light/dark)
  • displayMode, requestDisplayMode - Display control

References

Learn More

Install via CLI
npx skills add https://github.com/diegosouzapw/awesome-omni-skill --skill chatgpt-app-builder
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