How much world to build: the iceberg and the minimum structure
Worldbuilding has two failure modes. One is building too little, so that the rules contradict each other by the middle of the book. The other is building so much that chapter one never gets written. The second is far more common. Many writers have a continent map, a thousand-year timeline, and twelve gods, and no idea what the protagonist does in the first scene. This generator avoids the first failure without inviting the second: it produces the minimum structure a story needs to run, and nothing more.
That minimum has five parts. A single core rule: the one thing that makes this world different, phrased briefly and with many consequences ("magic manifests only in women"). The power structure the rule creates: who gains from it and who is pushed to the margins. The cost or taboo attached to the rule, because power that costs nothing kills tension. Geography and history, but only as much as is needed to explain the rule. And the seed of conflict: where the rule is under strain right now, and how the protagonist is caught in the crack. The sheet is delivered in that order.
Every genre carries conventions readers already know: gates and rank tiers in hunter fiction, empires and mage towers in fantasy romance, sects and cultivation stages in xianxia, the conditions of a regression. The tool uses those conventions as base material and layers your rule on top. Replace the conventions wholesale and readers exhaust themselves on exposition in chapter one; use only the conventions and the book is indistinguishable from a hundred others. Nine parts convention to one part invention is the realistic ratio for serial fiction.
The iceberg principle says the writer should know ten times what appears on the page. That is true, but the order matters: the ten times is accumulated while writing, not manufactured beforehand. The sheet this tool produces is the visible tip. When the draft raises a question ("is there a bank in this city?"), add an entry then. World detail that grows out of the draft fits the story far better than detail built in advance.
The free tool runs three times a day without an account, and nothing you enter is used for training. To keep the world sheet next to character sheets and the plot, and to have the AI respect the rules while drafting, use the Studio story bible, which also checks for continuity conflicts.