Play Killer Sudoku Online — Free

Killer Sudoku fuses Sudoku with Kakuro by overlaying “cages” — groups of cells whose digits must sum to a given total. Every standard Sudoku rule still applies (each row, column, and 3×3 box contains 1–9 exactly once), but you now also have the cage sums to satisfy, and no digit may repeat within a cage.

The cage constraints are often more powerful than the Sudoku constraints alone. A 2-cell cage summing to 3 must contain {1, 2}. A 3-cell cage summing to 6 must be {1, 2, 3}. These forced combinations eliminate candidates from the rows, columns, and boxes those cells belong to, dramatically accelerating the solving process.

Killer Sudoku is widely considered the most elegant Sudoku variant — it adds meaningful new logic without abandoning the core Sudoku framework. Many solvers find it more satisfying than standard Sudoku because the cage arithmetic provides an additional pathway when the grid logic stalls.

Use the “45 rule”: every row, column, and 3×3 box sums to 45. If a group of cages fits entirely within a box, their remaining total reveals the sum contribution of any cage that straddles the boundary — a powerful deduction unique to Killer Sudoku.