Killer Sudoku is a free online Sudoku variant that swaps most of the given digits for arithmetic. The 9x9 grid still needs 1 to 9 in every row, column and 3x3 box, but it is also carved into dotted "cages", each printed with a target total in its corner. The cells in a cage must add up to that total, and no digit may repeat inside a cage — which is what turns a nearly blank grid into a solvable puzzle. Twelve levels widen the cages from simple pairs up to five cells and thin out the starting digits, with level 11 giving you the traditional no-givens grid. Play instantly in the browser, no download and no account.
How to play Killer Sudoku
- Tap any empty cell to select it, then tap a digit from 1 to 9 on the number pad. Selecting a cell highlights every other cell in its cage.
- The small number in a cage's top-left corner is the total its cells must add up to.
- No digit may repeat inside a cage — so a two-cell cage totalling 4 is 1 and 3, never 2 and 2.
- The normal Sudoku rules still apply on top: every row, every column and every 3x3 box needs each digit from 1 to 9 exactly once.
- Fill the grid so every rule holds at once to clear the level. Later levels use wider cages and start with fewer digits already filled in — level 11 gives you none at all.
Tips
- Learn the forced cages. A two-cell cage totalling 3 can only be 1+2, a 4 can only be 1+3, a 16 can only be 7+9 and a 17 can only be 8+9. Those pin down digits before you have placed anything.
- Use the rule of 45: every row, column and 3x3 box sums to 45. If a box is covered by cages totalling 38 with one cell spilling outside it, that stray cell is 45 minus 38.
- A cage confined to a single row, column or box cannot reuse any digit that group already holds — the cage rule and the Sudoku rule stack, and that overlap is where most of the deduction comes from.
- Big cages carry less information than small ones. On the later levels, work outward from the tightest two- and three-cell cages instead of attacking a five-cell total head on.
- A wrong digit is flagged in red as soon as you place it, so a bad guess never quietly poisons a whole cage. You also get three hints per level, each revealing one correct cell.
FAQ
Is Killer Sudoku free to play?
Yes. Killer Sudoku is completely free to play online with no download, no account, and no in-game purchases.
Does Killer Sudoku work on mobile?
Yes. Cells and the number pad respond to touch as well as mouse clicks, and on desktop you can also use the number keys and arrow keys, so every level plays the same on phones, tablets and desktop.
What do the small numbers in the corners mean?
Each one is the target total for its cage — the group of cells joined by a dotted outline. The digits you place in that cage have to add up to exactly that number. The total is printed on the cage's top-left cell, and selecting any cell highlights the whole cage so you can see which cells it covers.
Can the same digit appear twice in one cage?
No. Every digit inside a cage must be different, even when the cage spans two different rows, columns or boxes. That is the rule that makes cage totals useful: a three-cell cage totalling 6 can only be 1, 2 and 3.
Is Killer Sudoku harder than regular Sudoku?
It depends on how comfortable you are with quick mental arithmetic. Killer Sudoku starts with far fewer given digits, which looks harder, but the cage totals carry a lot of information — an easy Killer grid can work out faster than a hard classic one. The early levels here use small cages and a generous scatter of starting digits to ease you in.
How many levels does Killer Sudoku have?
There are 12. They ramp on two axes: cages grow from two cells up to five, and the number of digits you start with thins out. Level 11 is the traditional Killer Sudoku with no given digits at all — the cages alone are enough to solve it. Every level can be replayed for a fresh grid.