TypeScript MCP Server on Bun: 60ms Cold Start (2026)

#mcp #typescript #bunjs #claude

Originally published at claudeguide.io/mcp-server-typescript-bun

TypeScript MCP Server on Bun: 60ms Cold Start (2026)

A TypeScript MCP server on Bun boots in ~60ms vs ~140ms on Node.js — a 2.3x cold-start edge for hosted, on-demand servers. The official @modelcontextprotocol/sdk runs on Bun without patches: stdio for Claude Desktop, HTTP+SSE for hosted services, single-file deploys via bun build --compile. Three Bun caveats: (1) fetch keep-alive defaults differ, (2) AbortController on streams needs an explicit listener, (3) read process.stdin directly — Bun's readline shim drops the JSON-RPC framing MCP requires.

When to choose TypeScript over Python

The Python MCP guide covers FastAPI servers. Pick TypeScript on Bun when:

Your team is full-stack TS. A Next.js shop already has Zod, tsconfig, and TS CI. Adding Python doubles the toolchain.
You need Bun's speed. Startup beats Node by ~80 ms and Python by ~250 ms — user-visible for MCPs spawned per-conversation by Claude Desktop.
You want to reuse Next.js types. Share a types/ package between MCP tools and web client. No drift between OpenAPI specs and TS interfaces.

Python wins when tools wrap pandas, scikit-learn, or libraries where the Python ecosystem is materially better. Otherwise TS on Bun is the 2026 default.

Minimal stdio server

The simplest MCP server registers one tool and reads JSON-RPC over stdin/stdout. Claude Desktop spawns the process, pipes requests in, and reads responses out.

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

const server = new Server(
  { name: "claudeguide-demo", version: "1.0.0" },
  { capabilities: { tools: {} } }
);

const EchoArgs = z.object({ message: z.string().min(1).max(1000) });

server.setRequestHandler("tools/list", async () =

## Streaming resources: SSE "tail logs" tool

MCP supports streaming responses via Server-Sent Events. Useful for long-running tools — log tails, build watchers, agent traces.