MCP Apps
MCP Apps let a tool return a small web interface instead of plain text. The host renders it in a sandbox next to the conversation.
An App is two things on your server: a tool whose _meta.ui.resourceUri points at a ui:// resource, and that resource, an HTML page served as text/html;profile=mcp-app. Hosts that do not support Apps still show the tool’s text result.
Guides
Section titled “Guides”- Your first MCP App: a dice roller built with the ext-apps SDK, tested in the reference basic-host.
- Run an MCP App in Claude, ChatGPT and VS Code: Content Security Policy rules, Claude’s
ui.domainformat, and what each host documents.
MCPDev is community documentation. It is not affiliated with the Model Context Protocol project or with the vendors of the clients it covers.