01 · The problem
Twelve clinics, twelve diaries, and a phone line. Double-bookings were routine and the front desk absorbed the consequences.
02 · The spec
Fourteen screens, thirty-one rules, forty-two acceptance criteria — most of them about what must not be possible. The rules that prevent a double-booking are the product.
03 · The build
Built test-first against those criteria, with each milestone reviewed by a senior engineer before it reached the clinics.
04 · The outcome
No double-bookings since launch, staff hours reclaimed, and a booking flow patients complete without calling.