Killer Sudoku
Killer Sudoku is Sudoku with no given digits. Instead, dashed cages cover the 9×9 grid, each with a sum in its corner: the digits in a cage add up to that sum and never repeat, and every row, column and 3×3 box still holds 1 to 9 once.
How to play
Every Killer Sudoku here has exactly one solution and can be solved by logic alone. Its level is the hardest technique it needs, from cage combinations and the rule of 45 at Easy to the rule of 45 across several units and pattern techniques at Hard.
- Each row, column and 3×3 box contains the digits 1 to 9 once.
- The digits in a cage add up to the number in its corner.
- No digit repeats within a cage.
- There are no given digits; the cages are the clues.
Playing on this site
- Select a cell, then type a digit or tap it on the number pad. Arrow keys move the selection.
- Turn on Notes (or press N) to pencil in candidates instead of answers.
- A cage's sum sits in its top-left cell; its notes move down to make room.
- Hint first points out any wrong digits, then names the next technique and shows where it applies before giving anything away.
- Your puzzle is saved in this browser, so you can come back to it later.
Techniques by level
Every technique the solver knows, from easiest to hardest. A puzzle's level is the hardest one it needs.
Easy
- Hidden single
- In the highlighted area, one digit fits in only one cell.
- Naked single
- The highlighted cell has only one possible digit left.
- Cage combinations
- Only a few sets of different digits add up to this cage's number, so the marked candidates are ruled out.
- Rule of 45
- Every row, column and box adds up to 45. Take away the cages inside it and the highlighted leftover cells have a known sum.
Medium
- Pointing
- Inside a box this digit fits only in one line, so it can't go elsewhere on that line.
- Claiming
- On this line the digit fits only inside one box, so it can't go elsewhere in that box.
- Naked pair
- Two cells share the same two candidates, so those digits leave the rest of their area.
- Cage and unit
- A digit this cage must contain sits in one line or box, or a line can only place a digit inside this cage. Either way, the marked candidates go.
- Hidden pair
- Two digits fit only in the same two cells, so those cells hold nothing else.
- Naked triple
- Three cells hold only three digits between them, so those digits leave the rest of their area.
- Hidden triple
- Three digits fit only in the same three cells, so those cells hold nothing else.
Hard
- Rule of 45 across units
- Neighbouring rows, columns or boxes add up to 45 each. Take away the cages inside them and the leftover cells have a known sum.
- X-Wing
- A digit is limited to the same two columns in two rows (or the reverse), so it leaves the rest of those lines.
- XY-Wing
- Whatever the middle cell holds, one of the two wings gets the shared digit, so cells seeing both wings can't.
- Naked quad
- Four cells hold only four digits between them, so those digits leave the rest of their area.
- Hidden quad
- Four digits fit only in the same four cells, so those cells hold nothing else.
- Swordfish
- A digit is limited to the same three columns in three rows (or the reverse), so it leaves the rest of those lines.
- XYZ-Wing
- One of these three cells must hold the shared digit, so cells seeing all three can't.
Questions
What is the rule of 45?
The digits 1 to 9 add up to 45, so every row, column and box sums to 45. Subtract the cages that lie fully inside a unit and the cells left over must make up the difference.
Where should I start a Killer Sudoku?
Look for cages with few ways to make their sum, such as 3 in two cells (only 1 and 2) or 17 in two cells (only 8 and 9). Then use the rule of 45 on rows, columns and boxes that are almost covered by cages.
Is Killer Sudoku free to play here?
Yes. Every level is free, with no account and no sign-in.