Chapter 28: Building Custom MCP Servers#

import { McpServer } from "@tina4/core";​const mcp = new McpServer("/api/my-tools", "My App Tools", "1.0.0");

mcp.registerRoutes(router);

import { McpServer, mcpTool, schemaFromParams } from "@tina4/core";​const mcp = new McpServer("/crm/mcp", "CRM Tools");​mcpTool("lookup_customer", "Find a customer by email", mcp, [  { name: "email", type: "string" },])((args) => {  return db.fetchOne("SELECT * FROM customers WHERE email = ?", [args.email]);});​mcpTool("recent_orders", "Get recent orders for a customer", mcp, [  { name: "customer_id", type: "integer" },  { name: "limit", type: "integer", default: 10 },])((args) => {  return db.fetch(    "SELECT * FROM orders WHERE customer_id = ? ORDER BY created_at DESC",    [args.customer_id], { limit: (args.limit as number) || 10 }  );});

{  "name": "lookup_customer",  "description": "Find a customer by email",  "inputSchema": {    "type": "object",    "properties": {      "email": {"type": "string"}    },    "required": ["email"]  }}

import { mcpResource } from "@tina4/core";​mcpResource("crm://product-catalog", "All active products", "application/json", mcp)(  () => db.fetch("SELECT id, name, price, category FROM products WHERE active = 1"));​mcpResource("crm://tax-rates", "Current tax rates by region", "application/json", mcp)(  () => db.fetch("SELECT region, rate FROM tax_rates"));

import { McpServer, schemaFromParams } from "@tina4/core";​const mcp = new McpServer("/accounting/mcp", "Accounting Tools");​class AccountingService {  constructor(private db: any) {}​  lookup(invoiceNo: string) {    return this.db.fetchOne(      "SELECT * FROM invoices WHERE invoice_no = ?", [invoiceNo]    );  }​  balances(minAmount = 0.0) {    return this.db.fetch(      "SELECT * FROM invoices WHERE paid = 0 AND total >= ?", [minAmount]    );  }​  summary(year: number, month: number) {    return this.db.fetchOne(      "SELECT SUM(total) as revenue, COUNT(*) as invoice_count " +      "FROM invoices WHERE strftime('%Y', created_at) = ? " +      "AND strftime('%m', created_at) = ?",      [String(year), String(month).padStart(2, "0")]    );  }}​const svc = new AccountingService(db);​mcp.registerTool("invoice_lookup",  (args) => svc.lookup(args.invoice_no as string),  "Find an invoice by number",  schemaFromParams([{ name: "invoice_no", type: "string" }]));​mcp.registerTool("outstanding_balances",  (args) => svc.balances((args.min_amount as number) || 0),  "List all unpaid invoices",  schemaFromParams([{ name: "min_amount", type: "number", default: 0.0 }]));​mcp.registerTool("monthly_summary",  (args) => svc.summary(args.year as number, args.month as number),  "Revenue summary for a month",  schemaFromParams([{ name: "year", type: "integer" }, { name: "month", type: "integer" }]));

// Secure the MCP routes via middlewareimport { secured } from "@tina4/core";​// Apply auth middleware before registering routesmcp.registerRoutes(router); // then protect the path with middleware

import { Auth } from "@tina4/core";​mcp.registerTool("sensitive_data",  (args) => {    const payload = Auth.validToken(args.token as string, secret);    if (!payload) return { error: "Unauthorized" };    return db.fetch("SELECT * FROM sensitive_table");  },  "Access restricted data",  schemaFromParams([{ name: "token", type: "string" }]));

// Test the tool function directlyfunction testLookupCustomer() {  const result = db.fetchOne("SELECT * FROM customers WHERE email = ?", ["alice@example.com"]);  assert(result !== null);  assert(result.email === "alice@example.com");}​// Test via MCP protocolfunction testMcpToolCall() {  const resp = JSON.parse(mcp.handleMessage({    jsonrpc: "2.0",    id: 1,    method: "tools/call",    params: {      name: "lookup_customer",      arguments: { email: "alice@example.com" },    },  }));  assert("result" in resp);  const content = resp.result.content[0].text;  assert(content.toLowerCase().includes("alice"));}

// src/routes/mcp/setup.tsimport { McpServer, mcpTool, mcpResource, schemaFromParams } from "@tina4/core";import { initDatabase } from "@tina4/orm";​const db = await initDatabase({ url: "sqlite:///crm.db" });​// Create MCP serverconst crmMcp = new McpServer("/crm/mcp", "CRM Assistant", "1.0.0");​// ToolsmcpTool("find_customer", "Search customers by name or email", crmMcp, [  { name: "query", type: "string" },])((args) => {  const q = args.query as string;  return db.fetch(    "SELECT * FROM customers WHERE name LIKE ? OR email LIKE ?",    [`%${q}%`, `%${q}%`]  );});​mcpTool("customer_orders", "Get all orders for a customer", crmMcp, [  { name: "customer_id", type: "integer" },])((args) => {  return db.fetch(    "SELECT o.*, GROUP_CONCAT(oi.product_name) as items " +    "FROM orders o LEFT JOIN order_items oi ON o.id = oi.order_id " +    "WHERE o.customer_id = ? GROUP BY o.id ORDER BY o.created_at DESC",    [args.customer_id]  );});​mcpTool("create_note", "Add a note to a customer record", crmMcp, [  { name: "customer_id", type: "integer" },  { name: "note", type: "string" },])((args) => {  db.execute("INSERT INTO customer_notes (customer_id, note) VALUES (?, ?)",    [args.customer_id, args.note]);  return { success: true };});​// ResourcesmcpResource("crm://products", "Product catalog", "application/json", crmMcp)(  () => db.fetch("SELECT * FROM products WHERE active = 1"));​mcpResource("crm://stats", "CRM statistics", "application/json", crmMcp)(() => {  const customers = db.fetch("SELECT COUNT(*) as count FROM customers");  const orders = db.fetch("SELECT COUNT(*) as count, SUM(total) as revenue FROM orders");  return {    customers: customers[0]?.count ?? 0,    orders: orders[0]?.count ?? 0,    revenue: orders[0]?.revenue ?? 0,  };});​// Register routescrmMcp.registerRoutes(router);​export { crmMcp };