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OPENAI_MCP_APPS_IN_CHATGPT_CHECKLIST
OPENAI_MCP_APPS_IN_CHATGPT_CHECKLIST
Type
External
Status
Published
Created
Mar 17, 2026
Updated
Mar 17, 2026

OpenAI “MCP Apps in ChatGPT” checklist#

Last verified: 2026-02-05

This is an implementation checklist for aligning mcp-app-studio (SDK) and
mcp-app-studio-starter (template/workbench) with OpenAI’s guidance that:

  • ChatGPT is an MCP Apps host (standard ui/* bridge).
  • window.openai is an optional, ChatGPT-only extension layer.

Protocol + metadata#

  • Tools that render a UI specify _meta.ui.resourceUri (string) on the tool descriptor.
  • Compatibility: accept legacy _meta["openai/outputTemplate"] (string) as an alias for _meta.ui.resourceUri.
  • Prefer emitting _meta.ui.resourceUri (do not emit openai/outputTemplate in new output).

MCP Apps UI bridge (host ↔ iframe)#

The core integration should use the MCP Apps UI bridge (JSON-RPC 2.0 over
postMessage), including:

  • ui/initialize
  • ui/notifications/tool-input
  • ui/notifications/tool-result
  • tools/call
  • ui/message
  • ui/update-model-context

ChatGPT-only extensions (window.openai)#

Only use these via feature detection + graceful fallback. Examples called out by OpenAI:

  • window.openai.requestCheckout(...)
  • window.openai.uploadFile(file)
  • window.openai.getFileDownloadUrl({ fileId })
  • window.openai.requestModal(...)

Additional frequently-used globals/APIs described in the Apps SDK reference:

  • window.openai.toolInput / window.openai.toolOutput / window.openai.toolResponseMetadata
  • window.openai.widgetState / window.openai.setWidgetState(state)
  • window.openai.callTool(name, args)
  • window.openai.sendFollowUpMessage({ prompt })
  • window.openai.openExternal({ href })
  • window.openai.notifyIntrinsicHeight(height)
  • window.openai.requestDisplayMode({ mode })

Docs + UX expectations#

  • README/docs describe ChatGPT as an MCP host (not a separate platform).
  • window.openai is explicitly documented as optional ChatGPT-only extensions.
  • SDK behaves well outside a host (no indefinite connect hangs; timeouts + clear errors).

Sources (OpenAI)#