Unfamiliar test data costs attention: every assertion needs you to remember what the record was supposed to contain. These APIs borrow worlds you already carry in your head, which leaves the whole of your attention for the part you are actually practising — the requests, the status codes and the headers.
The trade is deliberate. A mock API built on invoice line items makes you hold two unfamiliar things at once — the domain and the protocol — and the domain always wins, because it is the one you have to reason about to know whether the response was right. Borrowing a world you already know collapses that to one.
Start wherever the data is most familiar to you and work outward: list a collection, page through it, filter it, fetch one item, ask for one that does not exist. By the time the shape of the responses is boring, you are ready for the parts that are not — auth, conflicts, concurrency and the error codes each of these APIs is wired to produce on demand.
17 APIs in this category
Friends API — Characters, episodes & quotes from the coffee-house gang. (14 endpoints)
Movies API — QA-themed cinema. Sort, filter, rate. (9 endpoints)
Harry Potter API — Houses, students & spells from a magic school. (10 endpoints)
Star Wars API — Characters, planets & starships from a galaxy far away. (11 endpoints)
Sherlock Holmes API — Cases, suspects & clues from Baker Street. (10 endpoints)
Pokémon API — Creatures, trainers & simulated battles. (10 endpoints)
Middle-earth API — Fellowship, quests & artifacts from a fantasy realm. (9 endpoints)
The Office API — Employees, pranks & quotes from a paper company. (8 endpoints)
Marvel API — Avengers, villains & mission assignments. (10 endpoints)
GTA API — Characters, vehicles, weapons, missions, heists, a wanted system & radio stations across Los Santos, Vice City and Liberty City. (17 endpoints)
Dragon Ball API — Fighters, transformations, power levels & tournaments. (6 endpoints)