Slackbot · MCP testing
Test your MCP app's UI in Slackbot.
Slackbot renders MCP apps in inline and fullscreen mode, inside a up to 598px wide frame. Your app has to look right in that envelope. MCPJam renders it locally against Slackbot's real context so you see it before your users do.
npx @mcpjam/inspector@latestSlackbot's app envelope
Display modes
Slackbot supports inline and fullscreen, defaulting to inline. Your app has to hold up in each one.
Viewport
Apps render in a up to 598px wide frame on web. Design and test to that box, not to your dev browser.
Media placement
No tool-result media placement in Slackbot. Media returned by tools won't render in the app surface.
Theme
Slackbot'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
Probed: Verified by running against the client. Last reviewed 2026-07-08.
Walkthrough: Slackbot
Run npx @mcpjam/inspector@latest, connect the MCP server config you already use, and select Slackbot as the host. MCPJam emulates Slackbot with openai/gpt-5-nano 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 Slackbot's up to 598px wide 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 Slackbot. MCPJam emulates the host with openai/gpt-5-nano, so you can watch the real behavior locally, free and open source.
Slackbot renders apps in a up to 598px wide frame, supporting inline and fullscreen display modes. (Catalog last reviewed 2026-07-08.)
MCPJam's host-compat catalog (the same data behind caniuse.dev). Probed: Verified by running against the client. Last reviewed 2026-07-08.
See it in Slackbot before your users do.
One command, your existing server config, Slackbot's real behavior in the loop.
Open source · no credit card · ~2 min