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.

// Dedicated runtime for the MCP Apps demo.
//
// `mcpApps.servers` auto-applies the MCP Apps middleware to every registered
// agent: the middleware exposes the remote MCP server's tools to the agent at
// request time and emits the activity events that CopilotKit's built-in
// `MCPAppsActivityRenderer` renders inline as a sandboxed iframe.
const runtime = new CopilotRuntime({
  agents: { default: createMcpAppsAgent() },
  runner: new InMemoryAgentRunner(),
  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.
        serverId: "excalidraw",
      },
    ],
  },
});

No frontend renderer needed#

Unlike custom activity types, the MCP Apps renderer is already registered by CopilotKit 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 (
    <CopilotKitProvider runtimeUrl="/api/copilotkit-mcp-apps" useSingleEndpoint>
      <main className="p-8">
        <h1 className="text-2xl font-semibold mb-4">MCP Apps</h1>
        <p className="text-sm opacity-70 mb-6">
          Try: &ldquo;Use Excalidraw to draw a simple flowchart with three
          steps.&rdquo; The agent invokes a remote MCP tool and the associated
          UI resource renders inline in chat.
        </p>
        <CopilotChat />
      </main>
    </CopilotKitProvider>
  );

Transport types#

The middleware supports two transport types:

HTTP#

Use this format to connect to an MCP server that accepts standard HTTP requests:

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

SSE#

Use this format to connect to an MCP server that streams events over a persistent connection:

{
  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