chatgpt-app-builder

ChatGPT App Builder

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

The app is consumed by two users at once: the human and the ChatGPT LLM. They collaborate through the widget -- the human interacts with it, the LLM sees its state. The widget is your shared surface.

Before You Code

• Clarify what to build → [discover.md](references/discover.md): when starting a new app, validating an idea, or scoping features
• Design tools and widgets → [architecture.md](references/architecture.md): when deciding what needs UI vs tools-only, designing UX flows

Setup

• Scaffold and run → [setup.md](references/setup.md): when creating a new project, starting dev server, connecting to ChatGPT/Claude

Implementation

• Server handlers + widget creation → [server-and-widgets.md](references/server-and-widgets.md): when writing server.tool() with widgets, widget() helper, React widget files
• Widget state and LLM context → [state-and-context.md](references/state-and-context.md): when persisting state, triggering LLM from widget, managing ephemeral vs persistent data
• Display modes, theme, layout → [ui-guidelines.md](references/ui-guidelines.md): when adapting to inline/fullscreen/PiP, handling theme, device, locale
• Component API → [components-api.md](references/components-api.md): when using McpUseProvider, Image, ErrorBoundary, useWidget
• CSP and metadata → [csp-and-metadata.md](references/csp-and-metadata.md): when configuring external domains, dual-protocol metadata
• Advanced patterns → [widget-patterns.md](references/widget-patterns.md): when building complex widgets with tool calls, state, theming

Quick Reference

// Server
import { MCPServer, widget, text, object } from "mcp-use/server";
server.tool({ name: "...", schema: z.object({...}), widget: { name: "widget-name" } },
  async (input) => widget({ props: {...}, output: text("...") })
);

// Widget (resources/widget-name.tsx)
import { McpUseProvider, useWidget, type WidgetMetadata } from "mcp-use/react";
export const widgetMetadata: WidgetMetadata = { description: "...", props: z.object({...}) };
export default function MyWidget() {
  const { props, isPending, callTool, sendFollowUpMessage, state, setState, theme } = useWidget();
  if (isPending) return <McpUseProvider autoSize><div>Loading...</div></McpUseProvider>;
  return <McpUseProvider autoSize><div>{/* UI */}</div></McpUseProvider>;
}