Rulehunt
Sudoku with one hidden extra rule: read the digits the board refuses and work out what it is.
Every day: Two dailies, the same for everyone: a quick investigation of 15 to 20 open cells and a full daily board, each an ordinary sudoku with one extra rule hidden inside that you must work out and name. New puzzle: Once a day (the listing does not state the time).
Rulehunt is a sudoku game for iPhone where every board hides one extra rule. The board refuses any digit that breaks it, and your job is to explain the refusals, test a hypothesis and name the rule. Each day brings a quick investigation and a full board, the same for everyone.
About 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.
How to play Rulehunt
- Open Rulehunt and start the Quick investigation or the Full daily board.
- Fill in digits using ordinary sudoku rules.
- When the board refuses a digit, point at the visible digit you think caused it.
- Test hypotheses such as knight, king, neighbours or corners and see which fits the refusals.
- Name the hidden rule in your own words and finish the board.
Screenshots
Tips
- Refusals cost nothing, so try the digits you suspect early to gather evidence.
- Compare two refusals: the rule must explain both, which narrows the shapes quickly.
- Start with the common ones: knight's move, king's move and diagonal neighbours.
- Once you know the rule, use it as an extra constraint to finish the sudoku faster.
Questions
Is the Rulehunt daily the same for everyone?
Yes. The quick investigation and the full daily board are the same for everyone.
Is there a penalty for a wrong digit?
No. The board refuses digits that break the hidden rule, with no penalty.
Is Rulehunt free?
The lessons, the dailies and part of the other modes are free, with no ads or account. A single Full Game purchase opens the rest.
Do I need to know sudoku?
Basic sudoku rules help; five short lessons teach the hunt itself.
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