What is MCP? A Developer's Guide with Working Code

MCP stands for Model Context Protocol . It's an open standard that defines how AI models connect to external tools and data sources. Before MCP, every AI platform had its own way of doing tool integration. OpenAI had function calling. LangChain had its own tool format. Every agent framework invented its own interface. Build a tool for one system, it didn't work anywhere else. MCP fixes this. One protocol. Any client. Any tool server. Build once, work everywhere. The architecture in 30 seconds ┌─────────┐ MCP Protocol ┌─────────────┐ Your Code ┌──────────┐ │ Client │ ◄──────────────────► │ MCP Server │ ◄────────────────► │ APIs / │ │ (Claude) │ │ (your code) │ │ Data │ └─────────┘ └─────────────┘ └──────────┘ Client — The AI application. Claude Desktop, an IDE with AI, or any app that speaks MCP. Server — Your code. A program that exposes tools, resources, and prompts to the client. Transport — How they talk. stdio (local, stdin/stdout) or HTTP/SSE (remote, over the network). The client