Killer Sudoku

Killer Sudoku keeps every normal Sudoku rule — each row, column and 3×3 box holds the digits 1 to 9 once — and adds cages: groups of cells outlined with dashes, each with a small total in its corner. The digits in a cage must add up to that total, and no digit may repeat inside a cage.

On Easy some digits are given to help you start; on Hard and Expert only a handful are given — sometimes none — and the cage totals do almost all the work. Every puzzle is generated fresh and checked by a solver so it has exactly one solution.

1. Select a cell and type a digit, or use the number pad.
2. Fill every row, column and box with 1–9 once.
3. Make each cage add up to its total, without repeating a digit inside the cage.
4. Use Notes for pencil marks, Hint to reveal a cell and Mistakes to highlight wrong entries.

• Learn the unique sums. Two cells totalling 3 must be 1 and 2; totalling 17 must be 8 and 9. Three cells totalling 6 must be 1, 2 and 3.
• Use the 45 rule. Every row, column and box adds up to 45. If cages almost fill a box, the leftover cell's value is 45 minus the cage totals.
• Combine cages with Sudoku logic. Once a cage's digits are known, the rest of its row or box can't use them.