The previous article looked at the SDK's 34 built-in tools — file read/write, Bash execution, code search — covering common development scenarios. But an Agent's capabilities can't rely solely on built-in tools. You need to connect to databases, call enterprise APIs, and operate internal systems. These require a standardized integration approach. MCP (Model Context Protocol) is designed for exactly this. This article examines how Open Agent SDK uses the MCP protocol to bring external tools into the Agent Loop. What Is the MCP Protocol MCP is an open protocol proposed by Anthropic that defines communication standards between LLM applications and external tools/data sources. The concept: Tool side (MCP Server) exposes a set of tools, each with a name, description, and input schema Calling side (MCP Client) discovers tools, invokes them, and gets results through a standard protocol Communication is based on JSON-RPC with swappable transports Why does an Agent need this?…