How to play Killer Sudoku
Classic Sudoku rules, plus one twist: each dashed cage adds up to its small number. No repeated digits inside a cage.
Three familiar rules, one new clue
Fill every row, column and 3×3 box with 1–9 once each. A dashed cage is a connected group of cells: its digits must add to the small total in its corner, without repeating. A cage can cross a box boundary. A one-cell cage gives its digit directly.
Start with a small sum
A two-cell cage totalling 4 must contain 1 and 3, not 2 and 2. Their order is not yet known. If the first cell shares a column with an existing 1, it must be 3, and the second must be 1. Always check all the Sudoku constraints.
Use the remainder
A three-cell cage totals 16. If two of its cells are 4 and 7, the last is 16 − 4 − 7 = 5. Our hints explain this subtraction before you choose to apply it.
The rule of 45
The digits 1–9 add to 45. If complete cages entirely inside a row cover eight of its cells and total 39, the remaining cell is 6. Do not subtract an entire cage that extends outside the row; those extra cells are not part of its 45.
A quick exercise
Two empty cells in the same cage total 7. One cannot contain 1, 2 or 3 because of its neighbours. Is its value certain? No: the sets {1,6}, {2,5} and {3,4} all fit, so that cell could be 4, 5 or 6. A sum is not always enough to place a digit.
Practise without losing your classic game
Choose a cell, type a digit or use the number pad. Notes, undo and explainable hints are available. Games are generated with a complete chain of forced moves that verifies a unique answer. Progress is saved separately from classic Sudoku in this browser; it does not sync between devices. Switching styles starts a new puzzle immediately.