About killer sudoku
Killer sudoku is sudoku plus arithmetic. All the normal rules still apply — every row, column and 3×3 box holds the digits 1 to 9 exactly once — but the grid is also divided into dashed cages, and the digits inside each cage must add up to the small number printed in its corner. A digit cannot repeat inside a cage either, which is often the more useful of the two rules.
Most killer puzzles start with no digits at all, and this one is no exception. That sounds impossible and isn't: the cage sums carry the information the missing clues would have. A two-cell cage summing to 3 can only be 1 and 2. A three-cell cage summing to 6 can only be 1, 2 and 3. Those forced cages are the footholds everything else grows from.
How to play
Click or arrow-key to a square and type a digit. Select any square and the panel beside the board tells you how many digit combinations its cage allows — and when only one fits, it names it. Use Notes to pencil in candidates while you work a cage out.
Every puzzle here has exactly one solution, verified before it shipped. Killer grids are expensive to verify — proving uniqueness takes seconds per puzzle, not milliseconds — so they are generated and checked ahead of time rather than made up on the spot. You will never hit a board with two valid answers.
Reveals and checks are limited and add time to your result, so the leaderboard compares like with like. Unlike the classic game, a reveal here simply uncovers a square rather than naming a technique: cage arithmetic is the actual skill, and a row-and-column solver would have nothing honest to say about it.
