What does burn-test do?
The person who asks "and what does that cost?" Margins decide whether a good idea is a business. This skill finds them, with every number traceable to an input, and says plainly how many of those inputs are real.
Read ${CLAUDE_SKILL_DIR}/../receipts/rules.md first.
Tool in this folder:
python3 "${CLAUDE_SKILL_DIR}/unit_economics.py" founder/numbers.json --out founder/cfo.md
Step 1: gather the inputs
Write founder/numbers.json (shape: example.json in this folder, a walk-in
matcha café). It needs:
| field | what goes in it |
|---|---|
unit | what one sale is: a cup, an order, a client-month, a seat |
price | price per unit before tax |
variable | the cost of ONE unit: ingredients, packaging, shipping, card fees, per-sale commissions |
fixed_monthly | what you pay every month regardless: rent, salaries, software, insurance |
startup | one-off spend before opening: deposits, build-out, equipment, first inventory, launch ads |
plan_per_day | the volume once it is up and running |
ramp_per_day | 12 numbers: realistic volume in each month of year 1 |
capacity_per_day | the most you can physically sell in a day, if there is a limit |
Where the numbers come from, in this order:
- The user's own quotes, invoices, leases and supplier price lists.
- Public prices the user can check (a supplier's price list, a landlord's listing,
a payment processor's published fees). Write the source next to the number in
founder/cfo-sources.md. - Your estimate, clearly marked as an estimate, with the reasoning. Never present an estimate as a fact.
Log each input in the ledger, kind cost (or price for the price): a quote,
invoice, lease or published price page is MEASURED with its evidence id; an
estimate is PLANNED. The plan reports how many costs are backed.
Ask the user for anything only they know (rent quoted, wages they will pay). Use the
price from founder/pricing.md or founder/pitch.md if those exist.
The ramp is where plans lie. Month 1 is almost never the plan volume. If the
buyer panel ran, use its buy rate and first-month purchases to sanity-check the
ramp (founder/panel/results.md), and say how you did it. The panel's numbers
are an upper bound; if no real buyer has committed yet, the honest ramp is
lower than the panel suggests, never higher.
Step 2: run it
python3 "${CLAUDE_SKILL_DIR}/unit_economics.py" founder/numbers.json --out founder/cfo.md
It writes: the per-unit table and the contribution (what each sale leaves after its own costs), fixed costs, the break-even in units a day, the profit margin at the plan volume, year 1 month by month, the year 1 operating profit and the result after the startup spend, the cash needed before it pays for itself, the month the startup money is earned back, and a what-if table (price -10%, volume -20%, unit costs +15%). It flags a price below variable cost, a break-even above capacity, a losing year 1 and a payback beyond 12 months.
What-ifs without editing the file:
python3 "${CLAUDE_SKILL_DIR}/unit_economics.py" founder/numbers.json --price 7.00
python3 "${CLAUDE_SKILL_DIR}/unit_economics.py" founder/numbers.json --volume 0.8
Step 3: the CFO's note
Add a short section at the top of founder/cfo.md, in plain words:
- The hard truth: the number most likely to sink it, and how many of the inputs are quotes versus estimates ("4 of 11 costs are quoted; the ramp is a guess").
- The bad case: run
--volume 0.5and report it in one line. If there is no real demand evidence yet, this is as likely as the plan. - The margin: the profit margin at plan, and the contribution per unit.
- The line to watch: the one cost or assumption that moves the result most (usually the ramp, rent or the price), with the what-if that proves it.
- Cash: how much money the founder needs before it pays for itself.
- Three ways to improve the margin, each with the number it changes and by how much (run the what-if, do not guess).
- Whether the board's conditions about money (
founder/board.md) are met.
Rules
- Every number in your note comes from the tool's output or an input you can name.
- Every output of the model (margin, break-even, year 1, payback) is
PLANNED. Never call a projected margin "the real margin" or a result. - Revenue is before tax; say if the user's market adds sales tax on top.
- Not financial, tax or legal advice. Say once that an accountant should check the structure, payroll costs and tax before money moves.
Output
founder/numbers.json, founder/cfo.md, founder/cfo-sources.md. Next:
/kill-or-build uses these numbers for the verdict; /litmus if the
margin is thin.