Show HN: Step-by-step instructions to build your first ChatGPT Apps SDK app (opens in new tab)

I built a ChatGPT App using the new Apps SDK and wrote down all the steps so that you can follow along and do it yourself. It's definitely a game-changer to have rich UI experiences and the power of MCP right in the king of AI Chat apps.

This tutorial should tell you everything you need to get started. HMU or send PRs if you have ideas to improve the walkthrough.

Some observations in putting this together:

* ChatGPT seems to cache tool definitions and resources *

Every time I changed my code, I had to:

  1. Update the resource URI to cache-bust it.

  2. Manually refresh my tools list in the Connectors UI.

The system's backend currently is a bit slow so the cycle time suffers.

* There is a docs gap in handling tool vs. UI lifecycle *

Because there is a consent screen to submit tool inputs and call the tool, the HTML is rendered long before the tool output is available.

This doesn't seem to be reflected in the docs yet, so heads-up.

I found that you can listen on the window-level `openai:set_globals` event and defer handling of tool output until that time.