When you need this

There is a rule in your business that lives in somebody’s head. Which price this customer gets. Which of four contracts this booking falls under. Whether this combination is even possible. Whether this order needs a sign-off before it goes through.

Right now that rule is applied by a person on the phone — slowly, differently on different days, and only during office hours.

What I actually build

The rule written down first, in plain language, in a document we both sign off. Writing it down is where the disagreements about what the rule actually is come out — before they are built in.
The rule enforced by the site itself, on the server, where a customer cannot open the page and change the price.
The awkward cases decided in advance, not discovered by a customer: what happens at zero, at the maximum, on the last day of the season, when two conditions are true at once.
A screen where you change the numbers in the rule yourself — the discount, the minimum, the cut-off date — because numbers change far more often than the rule does. No developer in the loop.

Where this shows up in my work

A rental fleet with four contracts and one booking flow: four sets of rules underneath — day hire, seasonal, twelve-month, and rental an insurer pays for — one catalogue on top, and a customer who never has to know which one they are in. The price on the screen before the phone call, a demonstration build, does the same for a cleaning price: the rule runs on the page, so the number appears before anyone asks.

What you get

A rule that gives the same answer at three in the morning as on a Tuesday afternoon, and a written description of what it does — which is the document you will need the next time the business changes.