Killer Sudoku Online
Combine Sudoku’s row-and-box logic with dotted cages whose digits must add to the printed total.
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How to play
Place the digits 1 through 9 so each row, column and bold 3×3 box contains every digit exactly once.
Cells joined by a dotted outline form a cage. Its small total is the sum of the cage’s digits, and a digit cannot repeat inside a cage.
The number rules and cage rules apply together. Use the notes mode mentally or on paper when a cage has several possible combinations, then let its row, column and box remove candidates.
Strategy
Use the 45 rule: every row, column and 3×3 box sums to 45. If cages nearly cover a box, subtract their totals from 45 to find the remaining cells as one combined value.
Look for locked cage combinations. A two-cell cage totaling 16 can only be 7+9; if one cell’s column already contains 9, the order is fixed without trial and error.
Treat cage boundaries as information. When a cage crosses a box edge, the cells outside the box can be isolated by comparing the complete 45 total with the parts inside it.
Difficulty and variants
All variants use a 9×9 board. Easy puzzles contain more small or extreme-total cages; hard puzzles use roomier cages whose combinations stay ambiguous until Sudoku constraints narrow them.
Questions, answered
Can a number repeat in a Killer Sudoku cage?
No. Each digit in a cage must be different, even when the cage crosses a 3×3 box boundary.
What is the 45 rule in Killer Sudoku?
The digits 1 through 9 total 45, so every complete row, column and 3×3 box has that sum. Subtract known cage totals to find missing values.
Is Killer Sudoku harder than regular Sudoku?
It can be, but cages also provide extra clues. Easy Killer Sudoku often has more starting structure than a sparse classic puzzle.