This is the machine surface of Structs: REST queries against the chain, the transaction envelope every write travels in, the guild webapp catalog, and GRASS streaming. Skills tell you when to call; these pages tell you the path, the payload, and the traps.
Start at integration notes before you parse a response. Amounts are strings. Event details are encoded twice. Field names do not always match the CLI. If you skip that page you will invent a client that works on fixtures and fails on the network.
Queries are reads. Transactions are writes and they spend sequence numbers — one at a time per key, --gas auto, -- before entity IDs. The webapp API is the paginated catalog (lists, stats, settings) hosted by a guild, not by the chain binary. GRASS is the live stream; it will not give you history.
Open /api/ when you are building a client, a bot, or a Guild Stack query and need the map of the surface. If you are playing, you want skills and structsd, not these files. If you already know the entity, jump to queries by entity or webapp.