Rulehunt

Every Rulehunt board is an ordinary sudoku with one more rule tucked inside, such as cells a knight's move apart never holding the same digit. You are not told what it is. You solve as far as normal sudoku logic takes you, and when you try a digit the hidden rule forbids, the board refuses it with a red mark and no penalty. Every refusal is caused by a digit already on the board.

The hunt is to find that cause. You point at the visible digit you think explains the refusal and the board confirms or denies it. You can test hypotheses by lighting up the cells a knight's move away, the king's neighbours, the diagonals or the corners, and watching which explanation fits. Once you are sure, you name the rule in your own words and record it in a bestiary of twelve rules.

Each day has a quick investigation of 15 to 20 open cells and a full daily board, both the same for everyone, with a streak. Outside the dailies there are five short lessons, a mystery casebook of twelve cases, three expeditions of twelve boards that each end in an exam, and custom hunts.

Rulehunt is made by Suleyman Ozdemirci and came out in September 2026, in English, German, Japanese and Korean. It has no ads, no account and no tracking. The lessons, the dailies, the first expedition, three cases and three custom hunts a day are free; a single Full Game purchase opens the rest, with no subscription.