AgentHub Exercise

Build AgentHub yourself, one step at a time, with Claude Code.

AgentHub is a small, local, fictional university. Agents talk over the real A2A (Agent-to-Agent) protocol, through a University Hub: a Student agent, a Tutor, a Library and a Marketing 101 Professor. Agents can send interfaces (A2UI forms) inside their messages, and some of them think with Claude Haiku 5.5.

This repository has no app code. It holds what you need to build the app:

Folder	What it is
Steps-classroom/	The prompts to follow. Steps 0–9c, written for class: a Sonnet lead session plus cheap Haiku subagents working in parallel.
Steps/	The original build record: Steps 1–9 in the long form they were first written in. Read it to see how each step came about.
companion-site/	A teaching site that explains each step: what it changes, why, and how it works, on one evolving architecture diagram.

Before you start

• Node.js 20 or newer, and git.
• Claude Code. Use Sonnet as the main model (/model).
• An Anthropic API key, only for the optional "live" checks. Every step's required checks pass without one. Never commit the key: it goes in a .env file, which Step 0 tells git to ignore.

1. Open the teaching site

cd companion-site
npm start

Then open http://localhost:4440. It has no dependencies and needs no API key. Keep it open beside Claude Code: for each step, read what it is about, then build it.

2. Build the app, one step at a time

1. Open Claude Code in this folder (the repository root). Build here, not in a subfolder.
2. Paste the whole of Steps-classroom/00-setup-and-contracts.md as your message. Claude sets up the project and commits Step 0.
3. Then paste 01-…, 02-…, and so on up to 09c-…, one step at a time and in order. Each step ends when its Done when checks pass and Claude has committed Step N: ….
4. Between steps, look at what was built: run it, read the code, and compare it with that step's pages on the teaching site.

Steps-classroom/README.md explains how each step runs: contracts first, then parallel subagents, then join and check. Each step file starts with its time. Its "Cost" line is about the app's own model calls, which the required checks never make.

Claude Code usage is what costs money. In a full trial run of Steps 0–9c, Claude Code used about $27 of Sonnet and Haiku together and took about 2½ hours. Steps 0–2 cost under $1 together; Steps 5, 6 and 7a cost about $4 each.

If you already run something on ports 4444 or 41241–41244, stop it before you start: the steps check the app on those ports.

Follow one edition. The classroom edition is the one to build with. The original Steps/ files describe the same app in a different order and are not meant to be mixed with it.

Notes

• Everything runs on your own computer, on 127.0.0.1. All people, books and courses are fictional.
• Some steps ask Claude to add a section to "the README". It adds its notes about your app below this line.

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