What is MCP (Model Context Protocol)? Complete 2026 Guide TL;DR — Model Context Protocol (MCP) is an open JSON-RPC 2.0 specification, introduced by Anthropic in late 2024, that lets AI agents talk to external systems — file systems, databases, APIs, custom services — through a single standardized interface. An MCP server exposes capabilities (tools, resources, and prompts); an MCP client (Claude Desktop, Cursor, Zed, Sourcegraph Cody, your own agent) consumes them. Write the server onc...