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. Build once, work everywhere.