Build and run a local MCP server in TypeScript that exposes one or more model-callable tools, launched over the stdio transport using the official @modelcontextprotocol/server package.

Documented steps

1. Prerequisite: Node.js 20+.
2. Create the project: `mkdir weather && cd weather && npm init -y && npm pkg set type=module`. `type=module` is required — the SDK ships ES modules only.
3. Install the SDK and a schema library: `npm install @modelcontextprotocol/server zod tsx` (then `mkdir src`). `tsx` runs TypeScript directly with no build step.
4. Create `src/index.ts` with a minimal tool server: ```ts import { McpServer } from '@modelcontextprotocol/server'; import { serveStdio } from '@modelcontextprotocol/server/stdio'; import * as z from 'zod/v4'; function createServer(): McpServer { const server = new McpServer({ name: 'weather', version: '1.0.0' }); server.registerTool( 'get-alerts', { description: 'Get the active weather alerts for a US state', inputSchema: z.object({ state: z.string().length(2).describe('Two-letter US state code, e.g. CA') }) }, async ({ state }) => ({ content: [{ type: 'text', text: `alerts for ${state.toUpperCase()}` }] }) ); return server; } void serveStdio(createServer); console.error('weather MCP server running on stdio'); ```
5. The exact current API names: `McpServer` class and `registerTool(name, config, handler)` method (v2; replaces v1's `tool()`). `config.inputSchema` is a Zod (or any Standard Schema-compliant) object schema — the SDK derives the JSON Schema, validates arguments before the handler runs, and infers the handler's argument types from it.
6. Handlers return `{ content: [...] }` (a list of typed blocks: text/image/audio/resource_link/resource); set `isError: true` on the result to mark a failed call the model can read and react to, instead of throwing.
7. Serve over stdio with `serveStdio(createServer)` from `@modelcontextprotocol/server/stdio` (it owns the transport, reading stdin/writing stdout, and calls your factory per connection). Equivalently, the README shows the lower-level form: `const transport = new StdioServerTransport(); await server.connect(transport);`, imported from the same `/stdio` subpath.
8. Run it: `npx tsx src/index.ts`. Nothing prints to stdout — it waits on stdin for a host to speak first; your own log line goes to stderr via `console.error`, never `console.log` (stdout is the protocol channel).
9. Test with the MCP Inspector without a real host: `npx @modelcontextprotocol/inspector npx tsx src/index.ts`, then Connect → Tools tab → select and call the tool.
10. Docs: https://github.com/modelcontextprotocol/typescript-sdk, https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/main/docs/get-started/first-server.md, https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/main/docs/servers/tools.md