# Chatgpt App Builder

> 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.

- Skill: `diegosouzapw/chatgpt-app-builder-3` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add diegosouzapw/chatgpt-app-builder-3`
- Raw SKILL.md: https://api.skillmd.com/api/skills/diegosouzapw/chatgpt-app-builder-3/raw
- Safety review: pending (external: skill-scanner PASS, skillspector CAUTION)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: diegosouzapw (https://skillmd.com/u/diegosouzapw)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/diegosouzapw/chatgpt-app-builder-3

---


# ChatGPT App Builder

Build production-ready ChatGPT apps with interactive widgets using the mcp-use framework and OpenAI Apps SDK. This skill provides zero-config widget development with automatic registration and built-in React hooks.

## Quick Start

**Always bootstrap with the Apps SDK template:**

```bash
npx create-mcp-use-app my-chatgpt-app --template apps-sdk
cd my-chatgpt-app
yarn install
yarn dev
```

This creates a project structure:

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

## 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

## Creating Widgets

### Simple Widget (Single File)

Create `resources/weather-display.tsx`:

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

// Define widget metadata
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();
  
  // Always handle loading state first
  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;
```

That's it! The widget is automatically:
- Registered as MCP tool `weather-display`
- Registered as MCP resource `ui://widget/weather-display.html`
- Bundled for Apps SDK compatibility
- Ready to use in ChatGPT

### 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
    └── constants.ts
```

**Entry point (`widget.tsx`):**

```tsx
import { McpUseProvider, useWidget, type WidgetMetadata } from 'mcp-use/react';
import { z } from 'zod';
import { ProductCard } from './components/ProductCard';
import { FilterBar } from './components/FilterBar';

export const widgetMetadata: WidgetMetadata = {
  description: 'Display product search results with filtering',
  props: z.object({
    products: z.array(z.object({
      id: z.string(),
      name: z.string(),
      price: z.number(),
      image: z.string(),
    })),
    query: z.string(),
  }),
};

const ProductSearch: React.FC = () => {
  const { props, isPending, state, setState } = useWidget();
  
  if (isPending) {
    return <McpUseProvider autoSize><div>Loading...</div></McpUseProvider>;
  }
  
  return (
    <McpUseProvider autoSize>
      <div>
        <h1>Search: {props.query}</h1>
        <FilterBar onFilter={(filters) => setState({ filters })} />
        <div className="grid grid-cols-3 gap-4">
          {props.products.map(p => (
            <ProductCard key={p.id} product={p} />
          ))}
        </div>
      </div>
    </McpUseProvider>
  );
};

export default ProductSearch;
```

## Widget Metadata

Required metadata for automatic registration:

```typescript
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: Apps SDK metadata
  appsSdkMetadata: {
    'openai/widgetDescription': 'Interactive weather display',
    'openai/toolInvocation/invoking': 'Loading weather...',
    'openai/toolInvocation/invoked': 'Weather loaded',
    'openai/widgetCSP': {
      connect_domains: ['https://api.weather.com'],
      resource_domains: ['https://cdn.weather.com'],
    },
  },
};
```

**Important:**
- `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
- Default Apps SDK metadata is auto-generated if not specified

## useWidget Hook

The `useWidget` hook provides everything you need:

```tsx
const {
  // Widget props from tool input
  props,
  
  // Loading state (true = tool still executing)
  isPending,
  
  // Persistent widget state
  state,
  setState,
  
  // Theme from host (light/dark)
  theme,
  
  // Call other MCP tools
  callTool,
  
  // Display mode control
  displayMode,
  requestDisplayMode,
  
  // Additional tool output
  output,
} = useWidget<MyPropsType, MyOutputType>();
```

### Props and Loading States

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

```tsx
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:

```tsx
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:

```tsx
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

Request different display modes:

```tsx
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:

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

const server = new MCPServer({
  name: 'weather-app',
  version: '1.0.0',
});

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 }) => {
  // Fetch data from API
  const data = await fetchWeatherAPI(city);
  
  // Return widget with runtime data
  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:**
- `widget: { name, invoking, invoked }` on tool definition
- `widget({ props, output })` helper returns runtime data
- `props` passed to widget, `output` shown to model
- Widget must exist in `resources/` folder

## Static Assets

Use the `public/` folder for images, fonts, etc:

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

**Using assets in widgets:**

```tsx
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:

```tsx
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:

```tsx
import { Image } from 'mcp-use/react';

function MyWidget() {
  return (
    <div>
      <Image src="/images/photo.jpg" alt="Photo" />
      <Image src="data:image/png;base64,..." alt="Data URL" />
    </div>
  );
}
```

### ErrorBoundary

Graceful error handling:

```tsx
import { ErrorBoundary } from 'mcp-use/react';

function MyWidget() {
  return (
    <ErrorBoundary
      fallback={<div>Something went wrong</div>}
      onError={(error) => console.error(error)}
    >
      <MyComponent />
    </ErrorBoundary>
  );
}
```

## Testing

### Using the Inspector

1. **Start development server:**
   ```bash
   yarn dev
   ```

2. **Open Inspector:**
   - Navigate to `http://localhost:3000/inspector`
   
3. **Test widgets:**
   - Click Tools tab
   - Find your widget tool
   - Enter test parameters
   - Execute to see widget render

4. **Debug interactions:**
   - Use browser console
   - Check RPC logs
   - Test state persistence
   - Verify tool calls

### Testing in ChatGPT

1. **Enable Developer Mode:**
   - Settings → Connectors → Advanced → Developer mode

2. **Add your server:**
   - Go to Connectors tab
   - Add remote MCP server URL

3. **Test in conversation:**
   - Select Developer Mode from Plus menu
   - Choose your connector
   - Ask ChatGPT to use your 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' }"

## Best Practices

### Schema Design

Use descriptive schemas:

```typescript
// ✅ Good
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
const schema = z.object({
  city: z.string(),
  temp: z.number(),
});
```

### Theme Support

Always support both themes:

```tsx
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:

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

if (isPending) {
  return <LoadingSpinner />;
}

// Now safe to access props.field
return <div>{props.field}</div>;
```

### Widget Focus

Keep widgets focused:

```typescript
// ✅ 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

Handle errors gracefully:

```tsx
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

Set base URL for production:

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

### Environment Variables

```env
# Server URL
MCP_URL=https://myserver.com

# For static deployments
MCP_SERVER_URL=https://myserver.com/api
CSP_URLS=https://cdn.example.com,https://api.example.com
```

**Variable usage:**
- `MCP_URL`: Base URL for widget assets and CSP
- `MCP_SERVER_URL`: MCP server URL for tool calls (static deployments)
- `CSP_URLS`: Additional domains for Content Security Policy

## Deployment

### Deploy to mcp-use Cloud

```bash
# Login
npx mcp-use login

# Deploy
yarn deploy
```

### Build for Production

```bash
# Build
yarn build

# Start
yarn start
```

Build process:
- Compiles TypeScript
- Bundles React widgets
- Optimizes assets
- Generates production HTML

## Common Patterns

### Data Fetching Widget

```tsx
const DataWidget: React.FC = () => {
  const { props, isPending, callTool } = useWidget();
  
  if (isPending) {
    return <div>Loading...</div>;
  }
  
  const refresh = async () => {
    await callTool('fetch-data', { id: props.id });
  };
  
  return (
    <div>
      <h1>{props.title}</h1>
      <button onClick={refresh}>Refresh</button>
    </div>
  );
};
```

### Stateful Widget

```tsx
const CounterWidget: React.FC = () => {
  const { state, setState } = useWidget();
  
  const increment = async () => {
    await setState({ 
      count: (state?.count || 0) + 1 
    });
  };
  
  return (
    <div>
      <p>Count: {state?.count || 0}</p>
      <button onClick={increment}>+1</button>
    </div>
  );
};
```

### Themed Widget

```tsx
const ThemedWidget: React.FC = () => {
  const { theme } = useWidget();
  
  return (
    <div className={theme === 'dark' ? 'dark-theme' : 'light-theme'}>
      Content
    </div>
  );
};
```

## Troubleshooting

### Widget Not Appearing

**Problem:** Widget file exists but tool doesn't appear

**Solutions:**
- 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

**Problem:** Component receives empty props

**Solutions:**
- 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

**Problem:** Widget loads but assets fail

**Solutions:**
- Set `baseUrl` in server config
- Add domains to CSP via `appsSdkMetadata`
- Use HTTPS for all resources
- Check browser console for CSP violations

## Learn More

- **Documentation**: https://docs.mcp-use.com
- **Widget Guide**: https://docs.mcp-use.com/typescript/server/ui-widgets
- **Apps SDK Tutorial**: https://docs.mcp-use.com/typescript/server/creating-apps-sdk-server
- **ChatGPT Apps Flow**: https://docs.mcp-use.com/guides/chatgpt-apps-flow
- **Inspector Debugging**: https://docs.mcp-use.com/inspector/debugging-chatgpt-apps
- **GitHub**: https://github.com/mcp-use/mcp-use

## Quick Reference

**Commands:**
- `npx create-mcp-use-app my-app --template apps-sdk` - Bootstrap
- `yarn dev` - Development with hot reload
- `yarn build` - Build for production
- `yarn start` - Run production server
- `yarn 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
- `props` - Zod schema for input
- `exposeAsTool` - Auto-register as tool (default: true)
- `appsSdkMetadata` - Apps SDK configuration

**useWidget hook:**
- `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