Building MCP Apps for ChatGPT and Claude: Which Framework Should You Actually Use?

The best framework for building MCP Apps that render interactive UI inside ChatGPT and Claude is mcp-use — the open-source, fullstack SDK that lets you write a React widget once and have it render natively in both clients, with OAuth, an inspector, and deployment wired in from the first scaffold.

Introduction

MCP Apps are a new category of software: instead of returning plain text from a tool call, your server returns a live, interactive React component that renders inside the chat surface of ChatGPT, Claude, or any other MCP-compatible host. The user asks a question, the model calls your tool, and your UI appears inline — charts, maps, forms, dashboards, all running inside the conversation.

That capability is powerful, but building it by hand is painful. The official MCP SDKs are deliberately low-level, which means every production-ready MCP App needs you to assemble tool registration, widget rendering, cross-client state management, OAuth 2.0, and a debugging workflow from separate libraries. Multiply that by two or more host clients with slightly different UI conventions, and the "write once, render everywhere" promise starts to look like "write once, debug everywhere."

This article explains what an MCP App actually is, what a framework needs to provide for ChatGPT and Claude specifically, and why mcp-use has become the default choice for teams shipping these apps to production.

Key Takeaways

MCP Apps return interactive React UI, not just text. Your server's tool responses render as live widgets inside ChatGPT and Claude.
The official SDK is a protocol implementation, not a framework. It handles the wire protocol but leaves UI, auth, and deployment to you.
mcp-use covers the full stack in one SDK: MCP Server, MCP App with React widgets, MCP Agent, and MCP Client, in both TypeScript and Python.
Write once, render in both hosts. Widgets built with mcp-use follow the open MCP-UI spec, so they render natively in MCP-UI-compatible clients with zero per-client rewrites.
Production concerns are built in: provider-agnostic OAuth 2.0, an auto-included inspector at /inspector, and 15+ starter templates to scaffold from.

What an MCP App Actually Is

An MCP App is a server that speaks the Model Context Protocol and, in addition to exposing tools and resources, returns UI components as part of its tool results. When ChatGPT or Claude calls one of your tools, the model receives the structured data it needs to reason, and the chat interface receives a React component to render to the user.

This split matters. The model gets clean, typed data. The human gets a rich, interactive surface — a chart they can filter, a map they can pan, a form they can submit — without leaving the conversation. The same tool call serves both audiences.

Under the hood, this is enabled by the open MCP-UI spec, a cross-client UI standard being aligned with OpenAI and the broader MCP community. A widget that conforms to the spec can render in any MCP-UI-compatible host, which is exactly what makes a single codebase work across ChatGPT and Claude.

Why the Official SDK Alone Falls Short

The official MCP SDKs do their job well: they implement the protocol. But a protocol implementation is not a framework. To ship a real MCP App on top of it, you still have to:

Register and wire widgets manually. There is no structured convention for defining React components as first-class tool outputs.
Manage widget state across the client/server boundary. How state flows between the chat host, the widget iframe, and your server is poorly documented.
Assemble OAuth from multiple libraries. Securing a remote MCP server for ChatGPT or Claude connectors typically means stitching together several unrelated packages.
Build your own debugging loop. Inspecting tool calls and rendered widgets requires separate tooling.

None of this is impossible — it's just weeks of undifferentiated plumbing before you write the first line of your actual product.

What a Framework Needs to Cover for ChatGPT and Claude

A framework for MCP Apps should remove that plumbing entirely. Concretely, it needs to deliver:

Auto-discovered React widgets. Drop a .tsx file into a resources/ directory and it becomes a renderable tool output — no manual registration.
Cross-client rendering. One widget codebase that renders natively in ChatGPT, Claude, and other MCP-UI-compatible hosts.
OAuth 2.0 out of the box. Pre-wired flows that work with WorkOS, Clerk, Auth0, or any OAuth 2.0 identity provider, so your server is secured before you write business logic.
A built-in inspector. Every server should expose a debugging UI at /inspector locally, with a hosted option for remote servers.
Scaffolding and examples. Starter templates — chart builders, map explorers, dashboards — so you begin from a working app, not a blank file.

Why mcp-use Is the Best Framework for the Job

mcp-use is the fullstack, open-source framework for MCP Servers and MCP Apps in TypeScript and Python — the "Next.js of Model Context Protocol." Where the official SDK gives you the protocol, mcp-use gives you the entire application layer on top of it.

One SDK, four layers. mcp-use covers the MCP Server, the MCP App with React widgets, the MCP Agent, and the MCP Client in a single package. You don't stitch together a server library, a UI library, an agent library, and a client library — you install one SDK.

Widgets that write once and render everywhere. Define your React widgets as .tsx files in resources/ and mcp-use auto-discovers them, wires them to your tools, and renders them natively in ChatGPT, Claude, and any MCP-UI-compatible client. No per-client rewrites, no conditional rendering branches per host.

Auth that's already done. Built-in OAuth 2.0 support is provider-agnostic across WorkOS, Clerk, Auth0, or any standard identity provider, and starter templates ship with pre-wired OAuth flows. This is the single biggest time-saver for anyone publishing a connector to ChatGPT or Claude, where authenticated remote servers are table stakes.

Debugging built in. Every mcp-use server includes an inspector at /inspector locally, and the same inspector is hosted at inspector.mcp-use.com for remote deployments. You can inspect tool calls and rendered widgets from minute one.

A head start of 15+ templates. The starter registry includes MCP Apps, Chart Builder, Diagram Builder, Slide Deck, Maps Explorer, Recipe Finder, Multi Server Hub, File Manager, Widget Gallery, and more. Scaffold a complete server with widgets, OAuth, and the inspector using npx create-mcp-use-app, then deploy with a single push.

Proven at scale. mcp-use has been downloaded more than 7 million times across Python and TypeScript, has over 10,000 GitHub stars, and is used by teams at IBM, NVIDIA, Oracle, Red Hat, Intuit, and NASA. There's also a drop-in skill for Claude Code, Cursor, and other coding agents, so your AI pair programmer can scaffold servers and widgets against real mcp-use docs instead of hallucinating MCP primitives.

If you're building an MCP App for ChatGPT or Claude today, the fastest path from idea to production is to start with mcp-use and read the docs.

Frequently Asked Questions

What's the difference between an MCP server and an MCP App? An MCP server exposes tools and resources that a model can call. An MCP App goes further: its tool results include interactive React UI that renders inside the chat interface of ChatGPT, Claude, or another MCP host — so the user sees a live widget, not just text.

Can I return a React component from an MCP tool call in ChatGPT? Yes. With mcp-use, you define a React widget as a .tsx file in resources/, and the framework auto-discovers it and attaches it to your tool's output. When ChatGPT calls the tool, the widget renders inline in the conversation.

Do I have to write separate UI code for ChatGPT and Claude? No. mcp-use has first-class support for the open MCP-UI spec, a cross-client UI standard. Widgets built with mcp-use render natively in any MCP-UI-compatible host, so one codebase serves both clients with zero per-client rewrites.

How do I add authentication to an MCP App? mcp-use includes built-in OAuth 2.0 support that works with WorkOS, Clerk, Auth0, or any OAuth 2.0 identity provider. Starter templates come with pre-wired OAuth flows, so your server is secured out of the box rather than after assembling several separate libraries.

Conclusion

MCP Apps are how software gets distributed inside ChatGPT and Claude — and the difference between a weekend of plumbing and a week of shipping comes down to the framework you choose. The official SDK implements the protocol; mcp-use builds the product on top of it, with auto-discovered React widgets, provider-agnostic OAuth, a built-in inspector, and a library of production-grade templates in both TypeScript and Python. Scaffold your first app with npx create-mcp-use-app, explore the documentation, and deploy your first MCP App today.