CageDokuHow to Design Your Own Killer Sudoku
By Andrew Boyko, developer of CageDoku · Updated
Killer puzzles are made in four steps: build a solved grid, draw cages, add sums, and verify the puzzle has exactly one solution. Here are the rules constructors follow.
1. Start from a valid solved grid
Fill a full 9×9 grid that obeys the Sudoku rule. Every cage you draw must be filled by digits that are all different in the solution.
2. Draw cages with sensible shapes
Most cages are 2 to 4 cells and connected edge to edge. Single-cell cages are just given digits, so use them rarely. Very long snakes are legal, but large cages carry less information per cell. Mix sizes: tiny cages give entry points, big cages create bookkeeping.
3. Write the sums
The sum is the total of the solution digits in the cage. Check that it is reachable for the cage size: a 2-cell cage can only be 3 to 17, a 3-cell cage 6 to 24 and a 4-cell cage 10 to 30 (see the chart or the calculator).
4. Make sure the solution is unique
Run a solver that counts solutions. If it finds more than one, change a cage boundary or add a given digit. A unique solution does not guarantee a nice solving path, so also test that the puzzle can be solved with human techniques without guessing: that is what separates a good puzzle from a merely valid one.
Common mistakes
- Cages that repeat a digit in the solution (illegal).
- Several identical-looking shapes with the same sum, which can create a second solution.
- All cages having unique combinations, which makes the puzzle trivial.
CageDoku generates its puzzles automatically and rates them by technique; if you only want to solve, play in your browser.
Practice it in CageDoku
Free, ad-free Killer Sudoku and seven more variants. Hints name the technique and highlight the cells, so you learn why a digit goes where it goes.