Model Context Protocol Basics

The Model Context Protocol (MCP) standardizes how LLM applications connect to external tools and data sources. Where tool calling loop describes the in-conversation mechanics (tool calls and results inside the message history), MCP describes the plumbing: a client-server protocol where a host application (e.g. Claude Code) connects to MCP servers that expose tools, prompts, and resources.

What It Looks Like in Practice

• A minimal MCP server can be a single script: create the server, connect it to a client like Claude Code, and expose “run this script” as a callable tool.
• Servers can expose prompts (reusable prompt templates, invocable like tools — using-mcp-prompts) and resources (data the client can read), not just tools.
• The value is composability: one server, many clients; one client, many servers — instead of N×M bespoke integrations.
• Logging is a footgun: verbose MCP server logging flows straight into the agent’s context window; it must be treated as a context budget audit cost, not free observability.

Why It Matters

MCP decouples tool implementation from tool consumption. An agent harness (agent harness engineering) can grow its capability surface by plugging in MCP servers without changing its core loop — the same model provider abstraction logic applied to the tool side.

Related

tool calling loop, llm message protocol, agent native infrastructure, ag ui protocol, model provider abstraction.