Claude · MCP testing
Test your MCP app's UI in Claude.
Claude renders MCP apps in inline and fullscreen mode, inside a 720px wide × up to 5000px tall frame. Your app has to look right in that envelope. MCPJam renders it locally against Claude's real context so you see it before your users do.
npx @mcpjam/inspector@latestClaude's app envelope
Display modes
Claude supports inline and fullscreen, defaulting to inline. Your app has to hold up in each one.
Viewport
Apps render in a 720px wide × up to 5000px tall frame on web. Design and test to that box, not to your dev browser.
Media placement
Tool-result media is placed inline.
Theme
Claude'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
Assumed: Inferred defaults, not yet verified against the client. Last reviewed 2026-07-08.
Walkthrough: Claude
Run npx @mcpjam/inspector@latest, connect the MCP server config you already use, and select Claude as the host. MCPJam emulates Claude with anthropic/claude-haiku-4.5 on web, 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 Claude's 720px wide × up to 5000px tall frame, in inline and fullscreen 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 Claude. MCPJam emulates the host with anthropic/claude-haiku-4.5, so you can watch the real behavior locally, free and open source.
Claude renders apps in a 720px wide × up to 5000px tall frame, supporting inline and fullscreen display modes. (Catalog last reviewed 2026-07-08.)
MCPJam's host-compat catalog (the same data behind caniuse.dev). Assumed: Inferred defaults, not yet verified against the client. Last reviewed 2026-07-08.
See it in Claude before your users do.
One command, your existing server config, Claude's real behavior in the loop.
Open source · no credit card · ~2 min