MCP, the Model Context Protocol, is a standard way for an agent to use tools that live on someone else's server. An MCP server is a running program, listening for connections, that holds the real tools. The agent's MCP client is a mediator: each of its tools is a stand-in that forwards a call to the real tool on its …

Example motivation A shop's support agent handles refund requests, and a refund moves money: that is where the model should not be the one deciding. The model reads the customer's message: is it a refund request, which order, what reason. Only a model can read free text. Our code decides: it looks the order up in the …

RAG, retrieval-augmented generation, is text our code adds to a prompt before the model sees it. The agent searches the user's notes on every prompt, and puts the closest passages in front of it. The model answers from what the request holds. It still makes every decision: call a tool, or answer. The agent, the loop …

An AI agent is a program that runs a loop around a model. The user types a prompt. The model makes every decision: call a tool, or answer. The agent carries out the decisions, and keeps the conversation. A program around a model is also called its harness. The top bar picks the API: Anthropic Messages or OpenAI Chat …