MCP App Framework for Building, Testing, and Shipping Agentic Apps
Sunpeak is an open-source MCP App framework for building, testing, and shipping MCP Apps that run on ChatGPT, Claude, and every MCP-compatible host from a single codebase.
Definition
An MCP App framework provides development infrastructure for building interactive applications that run inside AI hosts via the Model Context Protocol (MCP). It includes project scaffolding, a local simulator, testing utilities, and deployment tooling.
What is an MCP App Framework?
MCP Apps are interactive applications built on the Model Context Protocol that run inside AI hosts like ChatGPT and Claude. They display rich UI components, handle user interactions, and connect to external services through MCP servers.
An MCP App framework handles the complexity of building these apps: project structure, local development, host simulation, testing, and deployment. Because MCP is a standard protocol, apps built with the right framework work across every compatible host without rewriting code.
Sunpeak is that framework. Write your app once, test it locally against any host's simulator, and ship it to ChatGPT, Claude, or any future MCP host from one codebase.
Write Once, Run on Every MCP Host
Your MCP App
One codebase, portable by default
ChatGPT
Claude
Any Host
Portable by Default
Your MCP App resources and tools work on any MCP host. Core sunpeak APIs like
useToolData,
useHostContext, and
useTheme abstract host differences
so your code stays the same.
Optional Host-Specific Features
Need ChatGPT-specific display modes or Claude-specific behaviors? Import from
sunpeak/chatgpt or
sunpeak/claude
subpaths. These features layer on top of your portable base without coupling your app
to one host.
Single Test Suite
Test once with the sunpeak simulator. The same test suite validates your app across host configurations, so you catch issues before deploying to any host.
Test MCP Apps Locally
Use the sunpeak simulator for MCP App testing locally and in CI/CD. The simulator replicates the MCP App runtime for deterministic UI testing across host configurations.
How sunpeak works
Scaffold a Project
Run sunpeak new to create
a new project with TypeScript, React, Vite, and MCP configuration pre-configured.
Develop Locally
Use the built-in MCP App simulator to develop and test your app without deploying. Hot Module Replacement (HMR) keeps your development loop fast.
Test Across Hosts
Validate your app works on ChatGPT, Claude, and other hosts using the simulator's host configuration. Connect to real hosts for integration testing with mock data and HMR.
Build and Ship
Run sunpeak build to generate
production bundles. Deploy to any MCP server or use the Sunpeak Resource Repository.
Core Framework Features
- Local MCP App Simulator
A React-based simulator that replicates the MCP App environment for local development and automated testing across hosts.
- MCP App Component Library
Pre-built UI components that work across MCP hosts, following host design guidelines.
- Built-in MCP Server
A development MCP server that serves your resources with mock data and hot module replacement.
- TypeScript-First APIs
Strongly typed hooks and utilities for interacting with the MCP App runtime, host APIs, and state management.
- Testing Infrastructure
Vitest and Playwright integration for unit and end-to-end testing of MCP Apps across host configurations.
- Resource Repository
Optional hosted runtime for deploying, sharing, and collaborating on MCP App resources.
Who sunpeak is for
Coding Agents
Agents like Claude Code, Codex, and Cursor can scaffold, build, and test MCP Apps with sunpeak's CLI and structured project conventions. No manual setup required.
React Developers
If you know React, you can build MCP Apps. Sunpeak uses familiar patterns: functional components, hooks, and JSX.
MCP Server Authors
Decouple your MCP App resources from your MCP server. Develop and version them independently with Sunpeak.
Teams Building for Multiple Hosts
Ship to ChatGPT, Claude, and other hosts without maintaining separate codebases. Sunpeak's portable APIs keep your team productive.
Getting Started
Install sunpeak globally and create a new project:
pnpm add -g sunpeak && sunpeak new
This scaffolds a complete MCP App project with TypeScript, React, Vite, and the sunpeak
runtime pre-configured. Run sunpeak dev to start the development server with the MCP App simulator.
Frequently Asked Questions
What is an MCP App framework?
An MCP App framework provides the development infrastructure for building interactive applications that run inside AI hosts via the Model Context Protocol (MCP). Sunpeak is an MCP App framework that includes a local simulator, pre-built UI components, testing utilities with Vitest and Playwright, and deployment tooling for building portable MCP Apps.
Do MCP Apps built with sunpeak work on ChatGPT and Claude?
Yes. Sunpeak MCP Apps are portable by default. Core APIs like useToolData and useHostContext work on every MCP host including ChatGPT and Claude. Host-specific features are opt-in through subpath imports like sunpeak/chatgpt or sunpeak/claude, so your base app code stays the same across all hosts.
How do I test MCP Apps locally?
Run "sunpeak dev" to start the local simulator and MCP dev server at localhost:6767. The simulator replicates the MCP App runtime with hot reloading so you can test all display modes, themes, and tool invocations without a paid ChatGPT or Claude account.
What is the difference between an MCP App framework and a ChatGPT App framework?
A ChatGPT App framework targets ChatGPT specifically. An MCP App framework like sunpeak targets the MCP standard, so apps work across ChatGPT, Claude, and other MCP-compatible hosts. Sunpeak is both — it provides a portable base with optional host-specific extensions.
Does sunpeak support host-specific features?
Yes. Import from sunpeak/chatgpt for ChatGPT-specific features like display modes and output templates, or sunpeak/claude for Claude-specific features. These layer on top of the portable base without coupling your app to one host.
Can I run MCP App tests in CI/CD?
Yes. Sunpeak includes Vitest and Playwright integration for automated MCP App testing. Create simulation files for deterministic UI states and run "pnpm test" for unit tests or "pnpm test:e2e" for end-to-end tests in your CI/CD pipeline.
Is sunpeak open source?
Yes. Sunpeak is MIT licensed and available on GitHub at github.com/Sunpeak-AI/sunpeak and npm at npmjs.com/package/sunpeak. It is free to use, modify, and distribute.
Open Source & MIT Licensed
Sunpeak is free to use, modify, and distribute.
Building specifically for ChatGPT? See the ChatGPT App Framework page.
