How to play
Fill the grid with the digits 1 to 9 so that every row, column and 3×3 box contains each digit once, exactly as in ordinary sudoku.
The grid is divided into cages outlined with dashed lines. The small number in the corner of a cage is the sum of its cells, and no digit may repeat inside a cage, even when the cage crosses into another box.
Apart from the occasional one-cell cage, whose sum simply is its digit, nothing is filled in for you. Every puzzle still has exactly one solution.
Strategy and tips
- Learn the cages with only one combination. Two cells adding to 3 must be 1 and 2; adding to 17, 8 and 9. Three cells adding to 6 are 1, 2 and 3, and adding to 24 are 7, 8 and 9. The sum combination table lists them all.
- Use the rule of 45. Every row, column and box adds up to 45. If the cages inside a box cover all but one of its cells, that cell is 45 minus their total. When a cage sticks out of a region, the cell that sticks out is the cage total minus whatever the region still needs. Medium sheets require this at least once.
- Combine cage sums with ordinary sudoku logic. A two-cell cage adding to 4 holds 1 and 3, so if it lies along a row, neither 1 nor 3 can appear anywhere else in that row.
- Hard sheets add locking between cages and lines, and pairs. Write notes in the cages early — the candidates are usually far fewer than in plain sudoku.
- The hint finds a cell where the cage sums leave only one possible digit.
Questions
- What do the levels mean?
- Easy sheets can be solved with cage combinations and sudoku basics, with cages of up to 4 cells. Medium sheets need the rule of 45 and use cages of up to 5 cells. Hard sheets need locking between cages and lines plus pairs, with cages of up to 6 cells.
- Can a digit repeat inside a cage?
- No. Within one cage every digit is different, even if the cage stretches across two boxes.
- Why does a new free game sometimes take a moment?
- Killer grids take more work to build and check than plain sudoku. Numbered sheets are prepared in advance and appear at once; the free game and the daily puzzle are built on your device in the background, which can take a second on an older phone.
- Is the solution unique?
- Yes. Every grid passes an exhaustive search before it is used, and it can also be reached with the logic of its level.