Schemas are the shapes. Mechanics tell you what a raid does; a schema tells you which fields exist on the planet you just queried and whether the ID is type-index or something else. Load one entity file, not the whole catalog, when context is tight.
Start with formats if you are about to parse an ID, and entities if you need the full object. Minimal schemas are the short projections for simple operations. Formulas are the math (load, capacity, damage) expressed so an agent can compute without scraping a prose page.
Requests, responses, errors, and validation are the HTTP envelope. Game-state, gameplay, economics, markets, and trading are domain aggregates. Database schema is the Guild Stack PostgreSQL map — different from the chain JSON, and the grid table will bite you if you join it wrong.
Open schemas when you are writing a parser, a Guild Stack query, or a fixture. If you are deciding whether to raid, you want combat and intel, not a JSON schema.