If you have started building tools for AI chat hosts, you have probably hit the same fork in the road. There are two ways to add a user interface to a tool right now. The first is MCP Apps, the open standard from the Model Context Protocol. The second is the OpenAI Apps SDK, the framework OpenAI shipped for the ChatGPT app store.
They both let your tool render a UI inside the chat. They both run inside a sandboxed iframe. They both talk to your server over JSON-RPC. So the question almost every developer is asking is the obvious one: are these competing standards?
The short answer
No. The OpenAI Apps SDK is built on top of MCP. It uses MCP for the wire format, the tool definitions, the UI rendering, and the security model. It then adds a thin layer with ChatGPT-specific extensions: a payment hook (window.openai.requestCheckout), a store directory, and a few helpers that only run inside ChatGPT.
So the choice is not "pick one or the other." The honest framing is:
