What do backend engineers write most often? Usually it is pulling data from a database and assembling nested JSON for frontend APIs. Take an agile project management API as an example. The frontend may want data like this: { "id": 1, "name": "Sprint 24", "stories": [ { "id": 10, "title": "User login", "tasks": [ { "id": 100, "title": "Design login page", "owner": { "id": 1, "name": "Ada" } } ] }