Killer Sudoku Online
Solve a real 9×9 Killer Sudoku where every row, column and box follows classic Sudoku rules while connected cages must reach their printed sums without repeated digits.
Sudoku placement plus cage arithmetic
Killer Sudoku keeps every classic 9×9 Sudoku rule and adds a second constraint layer. Each dashed cage has a target sum, digits may not repeat inside a cage, and the same digit still cannot repeat in a row, column or 3×3 box. That combination makes arithmetic useful without turning the puzzle into a calculation drill.
Use restricted cages first
Small cages with extreme totals are the easiest place to begin. Two cells totaling 3 must contain 1 and 2 in some order; two cells totaling 17 must contain 8 and 9. Once a row, column or box rules out one position, the order can become forced.
Read the remainder
Select any cage in the game to see the amount already entered, the remaining total and the legal unordered combinations for the empty cells. The helper does not tell you where those digits go, so you still need Sudoku placement logic.
Use the rule of 45
Every complete Sudoku row, column and 3×3 box contains 1 through 9 once, so its total is always 45. When several cages fit almost exactly inside one unit, subtracting their totals can expose the missing value or the total of a crossing cage fragment.
Five Practice tiers, one verified rule set
V0.183 has 50 independently verified Practice sources: ten Easy, ten Standard, ten Hard, ten Expert and ten Pure. Easy keeps sixteen starter digits, Standard twelve, Hard ten and Expert nine. Pure uses zero starter digits: only the connected cage sums and ordinary Sudoku rules remain. Each Expert source is separately re-proved unique after removing one Hard starter, and each Pure source is independently re-proved unique from cages alone. All 50 sources support eight Sudoku-preserving rotations/reflections, for 400 verified Practice transforms. Daily keeps the original Easy/Standard/Hard date mapping so existing Daily continuity is not rewritten.
The release checker does not accept a puzzle merely because it has a stored answer. It reruns a separate Sudoku-plus-cage solver and requires exactly one solution. The solver checks the 9×9 row, column and 3×3 constraints, each cage total and the no-repeat-within-a-cage rule. That gate matters because a visually plausible cage layout can still admit two valid grids.
During play, Notes stores candidates without changing the final value. Auto Notes recalculates candidates from the current row, column, box and exact viable cage assignments. Multi-select totals entered digits across selected cells, the selected-cage inspector exposes only currently viable combinations and lets you cross out combinations visually, and the independent calculator handles cages that are not on the current board. Explain Next Step recomputes a proof from the current grid rather than reading the stored final solution, while the 45 scan surfaces row, column or box sum deductions. Undo and Redo preserve play history; Check and Hint remain available and mark the review Assisted. Clean local best times therefore represent solves completed without either of those answer-level aids.
How to improve at Killer Sudoku
Do not try to calculate every cage from scratch. First scan for cages with only one or two possible digit sets. Then compare those sets with digits already fixed in the same row, column or box. Pencil marks are most useful when they represent a small set of real candidates rather than every digit that has not been ruled out yet.
Another useful habit is to look at cage boundaries that almost line up with a 45-point unit. If three complete cages inside a box total 37 and the only uncovered cell is part of a crossing cage, the uncovered contribution inside that box must be 8. That does not necessarily identify the cell immediately, but it creates a new arithmetic constraint for the crossing cage.
Because the game saves progress locally, a longer Hard puzzle can be closed and resumed without an account. Practice results do not change the main Today's 6 score, and the separate Daily Killer challenge maintains its own history and streak instead of being silently mixed into the six-game daily rotation.
What this page launches
This is not a separate thin quiz. It opens the same Killer Sudoku application used by the Practice catalog, with the same solver-verified source bank, local autosave, notes, cage-combination panel, Check, Hint, Undo/Redo and completion logic. The focused page exists only to explain the intent before sending you into the real game.