7. Writing an MCP server

ts
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { z } from "zod";

const server = new McpServer({ name: "invoices", version: "1.0.0" });

server.tool(
  "search_invoices",
  "Search invoices by customer and status. Returns at most 20 rows.",
  { customer: z.string(), status: z.enum(["open", "paid", "void"]).optional() },
  async ({ customer, status }) => {
    const rows = await db.invoices.find({ customer, status, limit: 20 });
    return { content: [{ type: "text", text: JSON.stringify(rows) }] };
  },
);

server.resource("invoice", "invoice://{id}", async (uri, { id }) => ({
  contents: [{ uri: uri.href, mimeType: "application/json", text: JSON.stringify(await db.invoices.get(id)) }],
}));

await server.connect(new StdioServerTransport());