The Cost Desk

Know the invoice before it arrives.

In production 13 chapters ~60 minutes One file, yours forever Works offline

In production — no buy button until the file exists

What it is

Know the invoice before it arrives.

Token economics without hand-waving: why long context charges you on every single turn, what caching actually caches, and when routing to a cheaper model first genuinely pays. Every rate on the page is an input you edit, and every figure is computed live from it — because quoted prices go stale and computed ones do not.

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Narrated end to end

Press play and a teacher talks you through the whole build, with a read-along transcript that highlights as it speaks.

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Demos on the page

Working, offline interactives — not screenshots. When the narration says "try it", the thing is right there.

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One file forever

No account, no app, no subscription. It runs from a single HTML file and will still run in ten years.

✅

Measured claims only

Every number is computed live on the page from inputs you can edit. Nothing is asserted that cannot be checked.

Who it is for

Written for whoever actually pays the AI invoice.

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Compute cost per task from first principles

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Lay out prompts so caching can do its job

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Compare routing strategies on your own workload

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Build a monthly spend estimate you can defend

Inside

13 chapters, the first four free

The free preview is not a teaser: those chapters are complete, and the paid chapters are physically absent from the preview file rather than hidden behind a script.

Welcome — and the live demo

What this hour is, how to use the page, and the interactive demo you will keep coming back to.

FREE

Chapter 1

Part of the free preview — the full narration, page content and exercises, nothing held back.

FREE

Chapter 2

Part of the free preview — the full narration, page content and exercises, nothing held back.

FREE

Chapter 3

Part of the free preview — the full narration, page content and exercises, nothing held back.

FREE

Chapter 4