What is Killer Sudoku?
Killer Sudoku (also called Sum Sudoku or Sumdoku) combines classic Sudoku with arithmetic cages. The 9×9 grid follows normal Sudoku rules — each row, column, and 3×3 box contains 1 through 9 — but instead of starting digits, the grid is divided into dashed cages, each showing the sum of the digits inside it. A digit can never repeat within a cage. From those sums alone, the entire grid can be deduced.
How to play:
- Choose a difficulty, then click Start Puzzle
- Tap or click a cell to select it, then tap a number button below the grid
- On desktop, you can also type numbers directly and move between cells with arrow keys
- Press Backspace, Delete, or the ✕ button to clear a cell
- Toggle ✏️ Notes mode to pencil in candidate digits — tapping a number adds or removes it as a small note in the selected cell
- The puzzle completes automatically the moment the grid is filled correctly
Key sum facts to memorize:
- A 2-cell cage summing to 3 must be {1,2}; summing to 17 must be {8,9}
- A 3-cell cage summing to 6 must be {1,2,3}; summing to 24 must be {7,8,9}
- Extreme sums always have the fewest combinations — start there
- The "rule of 45": every row, column, and 3×3 box sums to 45. If cages fit almost entirely inside a box, the leftover cell's value can be computed directly
Scoring:
- Solving Time: How long the puzzle took from start to solve
- Hints Used: Each hint fills one correct cell — fewer is better
- Every puzzle here is generated with exactly one solution