You want to build an MCP server in TypeScript. What package do you use and how does it handle schemas?

The official **TypeScript MCP SDK** is the `@modelcontextprotocol/sdk` package on npm. Install it with `npm install @modelcontextprotocol/sdk` (or pnpm add, bun add, etc.). The source lives at github.com/modelcontextprotocol/typescript-sdk, maintained by the protocol team. The SDK ships both server and client APIs. A minimal 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: "my-server", version: "1.0.0" }); server.tool( "add", { a: z.number(), b: z.number() }, async ({ a, b }) => ({ content: [{ type: "text", text: String(a + b) }] }), ); await server.connect(new StdioServerTransport()); ``` The Zod schema (`{ a: z.number(), b: z.number() }`) is converted automatically to JSON Schema that the host sends to the LLM. JSON-RPC plumbing, the initialize lifecycle, and stdio framing are inside `server.connect`. This SDK powers most community servers and nearly every Cloudflare Workers MCP server because TypeScript runs on Node, Bun, Deno, and Workers with the same code.

The official **TypeScript MCP SDK** is `@modelcontextprotocol/sdk` on npm (`npm install @modelcontextprotocol/sdk`), maintained at github.com/modelcontextprotocol/typescript-sdk. It is one of two first-party SDKs (the Python one is the other) and is the most widely used SDK across the broader MCP server ecosystem. The SDK ships both server (`McpServer`) and client (`Client`) APIs in one package. A minimal 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: "my-server", version: "1.0.0" }); server.tool( "add", { a: z.number(), b: z.number() }, async ({ a, b }) => ({ content: [{ type: "text", text: String(a + b) }] }), ); await server.connect(new StdioServerTransport()); ``` The **Zod pairing** is the design choice that defines the SDK. The Zod schema serves as the single source of truth for three things at once: runtime validation (Zod parses incoming arguments and rejects malformed input), TypeScript inference (the handler's `{ a, b }` is typed as `{ a: number, b: number }` without manual annotation), and JSON Schema for the LLM (the SDK converts the Zod schema to JSON Schema and emits it on tools/list). One declaration, three uses. The same pattern extends to `server.resource()` and `server.prompt()` for the other two MCP primitives. Transports include `StdioServerTransport` (default for local hosts), `StreamableHTTPServerTransport` (the 2026 standard for remote servers), and the deprecated `SSEServerTransport` (kept for backward compatibility only). The SDK runs on Node, Bun, Deno, and Cloudflare Workers, which is why most cloud-hosted MCP servers in 2026 are built with it.