Checkpoint: pack the window

Time to use the whole course on one prompt. You're building the help desk for Moon Café again, and this time it answers from the café's own info sheet instead of whatever it half-remembers.

A well-packed prompt for this has a clear shape. Stable parts first: who Claude is and how to answer, then the info sheet in a <document> with a <source>. In a real app this whole block is what you'd cache, because it's identical on every request. What changes goes last: the customer's question. In between, two habits that keep answers honest: quote first, and say so when the sheet doesn't cover it. And nothing else: no backstory, no old menus.

The left reply sounds helpful and is invented. The right one admits the gap because the prompt gave it permission to.

Checkpoint. Use this info sheet: Moon Café, open Mon–Fri 7am–6pm, Sat 8am–4pm, closed Sunday. Oat milk is free. Dogs welcome on the terrace. Write the whole prompt: Claude's job, the sheet wrapped in tags with a source, a request to quote first, permission to say the sheet doesn't cover something, a length limit, and a customer question at the end. Then try a question the sheet can't answer.

Finish this checkpoint and the Context is everything badge is yours. You can now say what fills a context window, why less is often more, how to lay out long documents and long chats, and how to make a stable prefix cheap. Next, Give your model tools lets Claude fetch context for itself, and Retrieval without tears picks the right pieces from a big pile.