Building a Javascript "Hello,World" MCP server in 2026

The Model Context Protocol (MCP) is Anthropic's open standard for connecting AI models to external tools and data sources. I'd been reading, (and talking), about it for months before building one for myself. After reading through several existingg posts that built around complex APIs, I decided to go as basic as possible with a simple hello-mcp — a minimal MCP server I built in an evening, starting from a single tool that says "Hello, World!" and ending with a dual-transport server with error handling, protocol logging, and a design I'm actually happy with. A moving target: how the MCP SDK has evolved The best way to build MCP servers in Node.js is using the official JavaScript SDK: @modelcontextprotocol/sdk . The McpServer class is the core abstraction: create an instance, register tools and resources on it, then connect it to a transport. Everything I built in this project sits on top of that. But, first a word of warning. If you're learning MCP from blog posts or tutorials, check th