Killer Sudoku
Classic sudoku rules, plus dashed "cages" that must add up to a target sum — and never repeat a digit inside.
What makes it Killer
Instead of starting with given digits, you start with cages — connected groups of cells with a printed target sum in the corner. Every cage must hit its sum exactly, with no repeated digits inside. The classic row, column, and box rules still apply on top.
Cage-sum arithmetic does most of the early work — innies, outies, and the 45-rule turn target sums into placements before you ever reach for elimination.
Stuck on a cage? The killer sudoku cage calculator lists every combination for a sum and cell count — with digit filters, magic-cage highlighting, and printable tables of all 502 combinations.
Rules
- All classic rules: no repeats in any row, column, or 3×3 box.
- Each cage's cells must sum to the printed target.
- No digit repeats within a single cage.
How Stillgrid plays
- Cage outlines and sums rendered cleanly into the grid.
- Pencil marks and auto-pencil for candidate tracking.
- Undo/redo with full history.
- Difficulty graded by the cage logic and singles a puzzle actually requires.
- Daily killer challenge alongside the classic one.
- Free to play. No signup needed to play.
Prefer a smaller grid?
Killer works beautifully at 6×6: digits 1–6, 2×3 boxes, and every row, column, and box summing to 21. The cage arithmetic is gentler, which makes 6×6 killer sudoku a quiet way in before the full 9×9 grid.
Common questions
What is killer sudoku?
Killer sudoku combines sudoku with cage-sum arithmetic. The grid usually starts with no given digits. Instead it is divided into dashed cages, each printed with a target sum, and every cage's cells must add up to that target with no repeated digit, on top of the classic row, column, and box rules.
How do you start a killer sudoku?
Start from the cage sums. A cage's target and size limit which digit combinations can fit, and techniques like innies, outies, and the 45-rule turn those sums into placements before you reach for normal elimination.
Can I play 6×6 killer sudoku online?
Yes. Stillgrid plays killer sudoku at both 6×6 and 9×9. On the 6×6 grid the digits are 1–6 and every row, column, and 2×3 box sums to 21, so the cage arithmetic is lighter — a good entry point.
Does killer sudoku on Stillgrid have ads?
No. Stillgrid has no ads and no signup is needed to play — killer sudoku included.
Is killer sudoku free on Stillgrid?
Yes. Killer sudoku and every other variant are free to play, with no signup needed to start a puzzle.