From Who Pays for the AI?
The Cost Sheet
One page per feature with a model inside it. Fill it in before you build, and again every time the sum changes: a new model, a new price, a new kind of customer. Keep the old sheets. The history is the useful part.
The unit
- What one press of the button causes
- One quote, one document read, one reply drafted. In the customer's words.
- What one unit costs
- From 30 real inputs, run the way the product will run them, with the check included. Write the figure near the expensive end, not the middle.
- Retries
- What share of attempts fail and go round again. Add that share to the unit cost.
The customer
- The heaviest sensible customer's busiest week
- Asked, not guessed. Who you asked, and when.
- Their month
- The busiest week times 4.
- Their model fees a month
- The unit cost times their month.
The price
- The price, and its shape
- Flat with a written limit, an allowance with a charge above it, or metered.
- The ratio
- Their model fees a month divided by the price. Under a tenth, build it. Over a tenth, pick one of the 4 ways out (code, a cheaper model, a different shape, a higher price) and fill in a new sheet.
The locks
- Sign-in before any model call
- Yes or no.
- Limit per account, in your code
- The number, and what happens when it's reached.
- Daily ceiling in your loop
- The ordinary number, and the higher one for the days the calendar warns you about.
- Hard cap at the provider
- The number, and the date you last watched it fire.
The door
- Where every model call goes through
- The one place in the code.
- How long inputs and outputs are kept
- And where your terms say so.
- The second option
- The model you would move to, roughly what it costs, and whether it passes your check.
The stop
- The number at which this feature has to justify itself
- Mine is a tenth of the price for 2 months running.
**Who you'd tell, and how, if you switched it off.**
From Who Pays for the AI?, Appendix A. The other forms are on the tools page.