Building a ChatGPT App Without a Paid Account or Developer Mode
The sunpeak ChatGPT App simulator running locally.
[Updated 2026-02-05] Want to build a ChatGPT App but don’t have a paid ChatGPT account? No problem.
TL;DR: Use sunpeak’s local ChatGPT simulator to build and test your entire ChatGPT App without a paid subscription.
OpenAI requires developer mode (and a paid subscription) to connect custom apps to ChatGPT. But you can build and test your entire ChatGPT App locally using sunpeak’s built-in ChatGPT simulator.
Quick Start
pnpm add -g sunpeak && sunpeak new
cd my-app
sunpeak devOpen http://localhost:6767. You now have a fully functional ChatGPT simulator running on your machine.
What You Can Do Locally
The simulator replicates the ChatGPT App runtime, so you can:
- Build and test your UI components
- Mock all tool responses and app states
- Switch between display modes and themes
- Iterate with hot reloading
Everything works exactly as it would inside ChatGPT.
When You Need the Real Thing
A paid account is only required when you want to:
- Deploy your app for others to use
- Test against ChatGPT’s actual AI responses
- Publish to the ChatGPT connector marketplace
Until then, the local simulator has everything you need to learn, experiment, and build.
Learn about the ChatGPT App framework | Documentation | Star us on GitHub
Frequently Asked Questions
Do I need a paid ChatGPT account to build a ChatGPT App?
No. You can build and test your entire ChatGPT App (built as an MCP App) locally using sunpeak's built-in ChatGPT simulator. A paid ChatGPT Plus or Team subscription is only required when you want to deploy your app for others to use or test against ChatGPT's actual AI responses.
What is the sunpeak ChatGPT App simulator?
The sunpeak simulator is a React component that replicates the ChatGPT App runtime environment. It runs locally on localhost:6767 and lets you build, test, and iterate on your ChatGPT App UI with hot reloading, without needing any ChatGPT account.
How do I install sunpeak and start building a ChatGPT App?
Run "pnpm add -g sunpeak && sunpeak new" to install sunpeak globally and create a new ChatGPT App project. Then run "sunpeak dev" in your project directory to start the local development server with the ChatGPT simulator at localhost:6767.
What features does the sunpeak ChatGPT App simulator support?
The sunpeak simulator supports all ChatGPT App display modes (inline, fullscreen, picture-in-picture), light and dark themes, tool invocations and mock responses, app state management, and hot module replacement for instant updates as you code.
When do I need a paid ChatGPT subscription for ChatGPT App development?
A paid ChatGPT Plus or Team account with developer mode is only required when you want to deploy your ChatGPT App to the real ChatGPT, test against ChatGPT's actual AI responses, or publish to the ChatGPT connector marketplace. Sunpeak lets you develop everything else for free.
Can I build production-ready ChatGPT Apps with the free sunpeak simulator?
Yes. The sunpeak simulator fully replicates the ChatGPT App (MCP App) runtime, so you can develop and test your entire app locally. When ready, use "sunpeak build" to create production bundles, then deploy to your MCP server.
What is an MCP server and do I need one for my ChatGPT App?
An MCP (Model Context Protocol) server provides your ChatGPT App resources to ChatGPT. Sunpeak includes a built-in MCP server for local development that runs on port 6766. For production, you'll need your own MCP server or can use the sunpeak Resource Repository.
