Use this skill whenever building, scaffolding, or debugging an MCP App — interactive UI rendered inside an MCP host (Claude, ChatGPT, Goose, MCPJam). Triggers include: any mention of 'MCP App', 'MCP UI', 'ext-apps', 'ui:// resource', 'structuredContent', 'AppConfig', 'callServerTool', 'ontoolresult', 'MCP interactive', 'MCP iframe', or requests to add a visual UI to an MCP tool. Also use when working with FastMCP AppConfig, ResourceCSP, tool visibility, postMessage communication between View and Host, or converting data transfer patterns (chunked binary, polling, file upload) into MCP App architecture. Covers: server setup (Python/FastMCP), view setup (Svelte/TypeScript), CSP security, data flow (content vs structuredContent), tool visibility, theming, display modes, chunked transfers, polling patterns, user file uploads, and the full JSON-RPC message reference. Do NOT use for standard MCP server tools without UI, or for general web development unrelated to the MCP Apps extension.
Software Development
