API Design Practice
Review APIs the way they actually ship, investigate contract failures from their symptoms, and identify the missing guarantee before proposing the redesign. There is usually more than one valid fix — the reasons are what get graded.
Review & investigate
Symptoms → evidence → root cause → redesign → prevention.
A new internal API is up for review before partners integrate; the author says it's “basically REST”.
A customer's card shows two identical charges 12 seconds apart for one checkout.
A partner's nightly sync intermittently misses orders and occasionally imports the same order twice.
Crash reports spike for mobile app versions older than 6 weeks, all in the account screen.
API p99 latency spikes to 30s and pods restart with out-of-memory kills every morning around 06:00.
An order was marked paid twice, releasing duplicate store credit to the customer.
Three partner integrations broke on Monday: dashboards render blank order states and one partner's automation cancelled valid orders.
The mobile dashboard takes 4–6 seconds to load on LTE while the same data renders instantly in the office.