Exactly one per row
Each horizontal line contains one cat — no more and no fewer.
Exactly one per column
Each vertical line contains one cat. A board of size N therefore has exactly N cats.
Exactly one per colored region
The board contains exactly N connected regions. Each region contains one cat, whatever its shape or area.
Cats never touch
Two cats cannot share an edge or a corner. Placing a cat rules out every surrounding cell.
Imported boards
A screenshot or hand-drawn board must have N connected regions and non-conflicting starter cats. If it is invalid, the solver reports no solution or multiple solutions instead of inventing an answer.