What is Killer Sudoku?
Killer Sudoku is a number-placement puzzle that blends standard Sudoku with arithmetic cages. The row, column and 3x3 box rules still apply, but there are usually no starting numbers.
Instead, the puzzle gives you cage totals. If a two-cell cage is marked 4, its cells must be 1 and 3 in some order. If a three-cell cage is marked 17, you know the digits must be a non-repeating combination that adds to 17.
- Every row contains the digits 1 to 9 once.
- Every column contains the digits 1 to 9 once.
- Every 3x3 box contains the digits 1 to 9 once.
- Every coloured cage adds to its printed total.
- Digits cannot repeat inside a cage.
How to play Killer Sudoku online
Start with the smallest cages. Single-cell cages give a fixed digit, while two-cell cages with totals like 3, 4, 16 or 17 have very few possible combinations.
Then combine cage sums with Sudoku placement. A cage that crosses a row, column or box can remove candidates from several places at once.
- Click or tap an empty cell.
- Use the number buttons or keyboard to place a digit.
- Turn on Notes to add small candidate digits.
- Use Auto notes to seed candidates from current Sudoku and cage rules.
- Use Check or Hint when you want a nudge.
Killer Sudoku difficulty levels
Easy puzzles include more small cages and direct totals. Medium puzzles use a balanced mix of two-cell and three-cell cages. Hard and Expert puzzles rely on larger cages, fewer immediate totals and more candidate work.
The generator checks each board for a single solution, then colours neighbouring cages differently so the puzzle stays readable without a cluttered cage outline.
- Easy: more direct cage totals and faster starts.
- Medium: a daily challenge with steady deduction.
- Hard: longer chains between cage sums and Sudoku regions.
- Expert: larger cages and fewer simple entries.
Killer Sudoku strategy tips
Learn common cage combinations. A two-cell cage totalling 3 must be 1 and 2; a two-cell cage totalling 17 must be 8 and 9. These tiny facts are the Killer Sudoku equivalent of obvious singles.
Watch where cages sit inside boxes. If a cage lies entirely inside one 3x3 box, its digits are locked into that box. If it spills across a boundary, the leftover cells in each region can become easier to calculate.
- Use small cage totals before scanning the whole grid.
- Look for cages contained inside a single row, column or box.
- Compare cage sums against the 45 total for each complete row, column and box.
- Keep notes tidy on hard puzzles.
- Avoid guessing; cage arithmetic usually gives another path.