These are the shapes most real integrations take: a cart whose stock runs out mid-checkout, a seat two people book at once, a transfer that would overdraw an account. Each one is small enough to hold in your head and strict enough that the interesting failures are reachable.
What makes these worth practising against is that the rules push back. A pizza that has been delivered cannot be cancelled; a seat that is taken cannot be booked twice; a transfer larger than the balance is refused rather than quietly allowed. Every one of those is a conflict your client has to handle, and none of them can be provoked against an API that only ever says yes.
They are also the closest thing here to the integrations you will actually be paid to test. If you want to rehearse a specific failure before production supplies it — a duplicate charge, an overbooked flight, a coupon that expired between the cart and the checkout — this is the group to reach for.
10 APIs in this category
Pizza Orders API — Place & track orders. Includes a guaranteed 500. (9 endpoints)
Coffee Shop API — Drinks & orders. Home of the legendary 418. (6 endpoints)
Football API — Teams, squads, standings & simulated matches. (7 endpoints)
Bank API — Accounts, transfers & cursor pagination. Home of the 402. (9 endpoints)
Shop API — Carts, stock drama & expired coupons. (9 endpoints)
Cargo Tracking API — Shipment state machines. Writes need an X-API-Key. (9 endpoints)
World Cup 2026 API — Teams, groups, venues, match simulation, tickets & bracket predictions across the 2026 host cities. (17 endpoints)
FIBA World Cup API — Teams, Doha arenas, quarter-by-quarter game simulation, box scores, coach challenges, cursor-paged play-by-play & ticketing. (22 endpoints)
Formula 1 API — Drivers, constructors, races, telemetry & pit stops. (7 endpoints)