mcp-ui

mcp-ui pioneered interactive UI over MCP before the MCP Apps extension existed. It now implements MCP Apps and keeps its original action protocol, which is what many deployed hosts (Goose, Postman, internal tools) still speak.

Two reasons to choose mcp-ui over plain ext-apps:

1. Delivery modes ext-apps does not have — externalUrl (point at a live app you already host) and remoteDom (stream a DOM description the client renders with its own components).
2. Host reach — a host that predates the MCP Apps extension will accept mcp-ui resources and its type:'tool'-style actions.

Packages: @mcp-ui/server, @mcp-ui/client. Ruby: mcp_ui_server.

Server: createUIResource