ChatGPT Apps SDK Development Guide Overview Create ChatGPT Apps with interactive widgets that render rich UI inside ChatGPT conversations. Apps combine MCP servers (providing tools) with embedded HTML widgets that communicate via the API. --- window.openai API Reference Widgets communicate with ChatGPT through these APIs: sendFollowUpMessage (Recommended for Actions) Send a follow-up prompt to ChatGPT on behalf of the user: Use for : Action buttons that suggest next steps (summarize, explain, etc.) toolOutput Send structured data back from widget interactions: Use for : Selections, form submi…