Build Your First MCP Server in Under 100 Lines of JavaScript

What is MCP? Model Context Protocol (MCP) is an open standard by Anthropic that lets AI assistants like Claude connect to external tools, data sources, and services. Think of it as a USB-C port for AI — one standard connector that works with any compatible device. Before MCP, every AI integration was bespoke. Want Claude to query your database? Custom plugin. Want it to call your API? Another custom integration. MCP standardizes all of this with a clean protocol that any AI client can speak. The killer insight: you write the server once, and it works with Claude Desktop, Cursor, Continue, and any other MCP-compatible client. The Protocol in 60 Seconds An MCP server exposes three primitives: Tools — functions the AI can call (e.g. search_database , send_email ) Resources — data the AI can read (e.g. files, database records) Prompts — reusable prompt templates For most integrations, tools are all you need. Communication happens over stdio (subprocess) or SSE (HTTP). The client discovers