Module 1 · What agents are · Lesson 2

Tools and the agent-computer interface

How tool calling works on the wire, how to design tools a model uses correctly, and how MCP lets one tool server work in many harnesses.

75 min 1 video 3 exercises 7-question quiz Answers

Setup for the exercises:Install Claude Code Node.js, pnpm and TypeScript MCP servers in Claude Code

By the end of this lesson you can

Describe the request-response cycle of a tool call, including tool definitions, tool_use and tool_result blocks
Design a tool's name, description, input schema, output and error messages for an agent rather than a human programmer
Apply mistake-proofing (poka-yoke) to a tool you design, and estimate the token cost of a tool's output
Explain what MCP standardises, and connect a TypeScript tool to Claude Code as a script or an MCP server

In lesson 1, the agent "read" an official copy. The model didn't open anything; it asked, and the harness did the work. That request is a tool call, and tools are how an agent touches the world. They are also where most agent bugs start: a tool with a vague description gets called at the wrong time, a tool that returns 40 pages of lease floods the context, and a tool that accepts any string gets a title number in the wrong format. This lesson covers the mechanics of tool calling and then the design discipline Anthropic calls the agent-computer interface.

Module 1 · What agents are · Lesson 2

Tools and the agent-computer interface

How tool calling works on the wire, how to design tools a model uses correctly, and how MCP lets one tool server work in many harnesses.

75 min 1 video 3 exercises 7-question quiz Answers

Setup for the exercises:Install Claude Code Node.js, pnpm and TypeScript MCP servers in Claude Code

By the end of this lesson you can

Describe the request-response cycle of a tool call, including tool definitions, tool_use and tool_result blocks
Design a tool's name, description, input schema, output and error messages for an agent rather than a human programmer
Apply mistake-proofing (poka-yoke) to a tool you design, and estimate the token cost of a tool's output
Explain what MCP standardises, and connect a TypeScript tool to Claude Code as a script or an MCP server

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3 hands-on exercises
A 7-question quiz
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