MCP Apps

What is this?

MCP Apps are MCP servers that expose tools with associated UI resources. When the agent calls one of these tools, CopilotKit automatically fetches the resource and renders the UI component in the chat — no additional frontend code required.

Key benefits:

• Zero frontend code — UI components are served by the MCP server
• Full interactivity — components can use HTML, CSS, and JavaScript
• Secure sandboxing — content runs in isolated iframes
• Thread persistence — MCP Apps are stored in conversation history and restored on reconnect

Wire the runtime to your MCP server(s)

A single mcpApps.servers entry on the runtime is all it takes. The runtime auto-applies the MCP Apps middleware to every registered agent: each time an agent calls a tool backed by an MCP UI resource, the middleware fetches the resource and emits an activity event that the built-in MCPAppsActivityRenderer renders inline in the chat as a sandboxed iframe.

// The `mcpApps.servers` config is all you need server-side. The runtime
// auto-applies the MCP Apps middleware to every registered agent: on each
// MCP tool call it fetches the associated UI resource and emits an
// `activity` event that the built-in `MCPAppsActivityRenderer` renders
// inline in the chat.
const runtime = new CopilotRuntime({
  // @ts-ignore
  agents: {
    "mcp-apps": mcpAppsAgent,
    // headless-complete shares this runtime because its cell also exercises
    // MCP Apps rendering (via a hand-rolled `useRenderActivityMessage` in
    // `use-rendered-messages.tsx`).
    "headless-complete": headlessCompleteAgent,
  },
  mcpApps: {
    servers: [
      {
        type: "http",
        url: process.env.MCP_SERVER_URL || "https://mcp.excalidraw.com",
        // Always pin a stable `serverId`. Without it CopilotKit hashes the
        // URL, and a URL change silently breaks restoration of persisted
        // MCP Apps in prior conversation threads.
        serverId: "excalidraw",
      },
    ],
  },
});

No frontend renderer needed

Unlike custom activity types, the MCP Apps renderer is already registered by CopilotKitProvider out of the box. A plain <CopilotChat /> is enough — no renderActivityMessages prop, no manual useRenderActivityMessage wiring.

  // No `renderActivityMessages`, no `useRenderActivityMessage` — the
  // CopilotKitProvider auto-registers the built-in `MCPAppsActivityRenderer`
  // for the "mcp-apps" activity type. A plain <CopilotChat /> is enough.
  return (
    <CopilotKit runtimeUrl="/api/copilotkit-mcp-apps" agent="mcp-apps">
      <div className="flex justify-center items-center h-screen w-full">
        <div className="h-full w-full max-w-4xl">
          <Chat />
        </div>
      </div>
    </CopilotKit>
  );

Transport types

The middleware supports two transport types:

HTTP

{
  type: "http",
  url: "http://localhost:3101/mcp",
  serverId: "my-http-server"
}

SSE

{
  type: "sse",
  url: "https://mcp.example.com/sse",
  headers: {
    "Authorization": "Bearer token"
  },
  serverId: "my-sse-server"
}

Example MCP servers

Try these open-source MCP Apps servers to get started:

• Excalidraw — collaborative whiteboard rendered in-chat
• modelcontextprotocol/ext-apps — canonical reference implementations

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