ChatGPT · MCP testing
Test your MCP app's UI in ChatGPT.
ChatGPT renders MCP apps in inline, fullscreen, and pip mode, inside a up to 768px wide × 400px tall frame. Your app has to look right in that envelope. MCPJam renders it locally against ChatGPT's real context so you see it before your users do.
npx @mcpjam/inspector@latestChatGPT's app envelope
Display modes
ChatGPT supports inline, fullscreen, and pip, defaulting to inline. Your app has to hold up in each one.
Viewport
Apps render in a up to 768px wide × 400px tall frame on desktop. Design and test to that box, not to your dev browser.
Media placement
Tool-result media is placed inline.
Theme
ChatGPT's context reports a dark theme, pointer input (no touch). Test your app's contrast there.
Local, no tunnel
MCPJam's App Builder emulates the app locally and previews across viewports, with no ChatGPT subscription and a built-in tunnel when you need to test in a real client.
How we know
Vendor docs: Based on the vendor's published documentation. Last reviewed 2026-07-08.
Walkthrough: ChatGPT
Run npx @mcpjam/inspector@latest, connect the MCP server config you already use, and select ChatGPT as the host. MCPJam emulates ChatGPT with openai/gpt-5-nano on desktop, so what you see is this host's behavior, not a generic client's.
Open your app in the App Builder preview: it renders in ChatGPT's up to 768px wide × 400px tall frame, in inline, fullscreen, and pip mode, with no subscription needed and a built-in tunnel when you need to test in a real client. Resize across the previews and confirm nothing clips.
Frequently asked questions
Run npx @mcpjam/inspector@latest, connect your server, and select ChatGPT. MCPJam emulates the host with openai/gpt-5-nano, so you can watch the real behavior locally, free and open source.
ChatGPT renders apps in a up to 768px wide × 400px tall frame, supporting inline, fullscreen, and pip display modes. (Catalog last reviewed 2026-07-08.)
MCPJam's host-compat catalog (the same data behind caniuse.dev). Vendor docs: Based on the vendor's published documentation. Last reviewed 2026-07-08.
See it in ChatGPT before your users do.
One command, your existing server config, ChatGPT's real behavior in the loop.
Open source · no credit card · ~2 min