examples/basic-server-preact/server.ts

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import type { CallToolResult, ReadResourceResult } from "@modelcontextprotocol/sdk/types.js";
import fs from "node:fs/promises";
import path from "node:path";
import { registerAppTool, registerAppResource, RESOURCE_MIME_TYPE } from "@modelcontextprotocol/ext-apps/server";
import { startServer } from "./server-utils.js";

const DIST_DIR = path.join(import.meta.dirname, "dist");

/**
 * Creates a new MCP server instance with tools and resources registered.
 */
function createServer(): McpServer {
  const server = new McpServer({
    name: "Basic MCP App Server (Preact)",
    version: "1.0.0",
  });

  // Two-part registration: tool + resource, tied together by the resource URI.
  const resourceUri = "ui://get-time/mcp-app.html";

  // Register a tool with UI metadata. When the host calls this tool, it reads
  // `_meta.ui.resourceUri` to know which resource to fetch and render as an
  // interactive UI.
  registerAppTool(server,
    "get-time",
    {
      title: "Get Time",
      description: "Returns the current server time as an ISO 8601 string.",
      inputSchema: {},
      _meta: { ui: { resourceUri } },
    },
    async (): Promise<CallToolResult> => {
      const time = new Date().toISOString();
      return { content: [{ type: "text", text: time }] };
    },
  );

  // Register the resource, which returns the bundled HTML/JavaScript for the UI.
  registerAppResource(server,
    resourceUri,
    resourceUri,
    { mimeType: RESOURCE_MIME_TYPE },
    async (): Promise<ReadResourceResult> => {
      const html = await fs.readFile(path.join(DIST_DIR, "mcp-app.html"), "utf-8");

      return {
        contents: [
          { uri: resourceUri, mimeType: RESOURCE_MIME_TYPE, text: html },
        ],
      };
    },
  );

  return server;
}

async function main() {
  if (process.argv.includes("--stdio")) {
    await createServer().connect(new StdioServerTransport());
  } else {
    const port = parseInt(process.env.PORT ?? "3001", 10);
    await startServer(createServer, { port, name: "Basic MCP App Server (Preact)" });
  }
}

main().catch((e) => {
  console.error(e);
  process.exit(1);
});