A quote calculator from a single brief

Steps

1. Describe what the calculator works out

   Before writing to Claude, note down: which services you sell, at what price, when there is a discount and whether prices include VAT. The more concrete the numbers, the less the model has to guess.

2. Paste the brief

   Copy the template, replace the prices with your own and send it in a new chat.

   Goal: a quote calculator for a cleaning company.
   User: a customer on a phone, no sign-up.
   Inputs: area in m² (10–500), type of cleaning
   (deep 3.00 €/m²; regular 1.50 €/m²),
   number of windows (4.00 € per window).
   Rules: above 120 m² — 10% discount
   on cleaning (not on windows).
   Prices exclude VAT; show 20% VAT and total.
   Result: one HTML file with built-in CSS and JavaScript,
   no external libraries, readable on a phone,
   with a label on every field and a message for an invalid area.
   Show the breakdown: cleaning, discount, windows,
   before VAT, VAT, total — rounded to 0.01 €.

   Copy

3. Save and open the file

   Copy the code from the answer into a text editor and save it as calculator.html (choose “All files”, not .txt). Double-click to open it — the calculator appears in the browser.

4. Ask for one change

   Send only one change at a time and ask for everything else to stay the same. That way you can easily see what changed.

   Add a “Copy quote” button that copies the breakdown as text. Do not change the calculations or the layout.

   Copy

Check it yourself

• The discount applies only to cleaning, not windows
• The fields have labels and work on a phone
• If a result is wrong, give Claude the exact case and the expected number