Killer sudoku
Sudoku with sums — every cage must add up.
Click a square or use the arrow keys, then type 1–9. Each dashed cage must add up to its number with no digit repeated. N turns notes on and off, Shift + digit adds a note, Backspace erases, Ctrl+Z undoes.
Nothing leaves your device
This tool runs entirely in your browser. What you type, play or record here stays on your device: nothing is uploaded or saved on a server.
Example
Example: the cages with only one way to make their sum, and the 45 rule
Most killer sudokus start with the cages that can be filled in only one way. These are the ones the combinations helper shows with a single set; spot them first, then use the 45 rule on the boxes.
- A three-square cage of 15 has eight sets, from 1 + 5 + 9 to 4 + 5 + 6. Put a 6 in it and the helper crosses out five: only 1 + 6 + 8, 2 + 6 + 7 and 4 + 5 + 6 are left.
- The 45 rule: if three cages lying wholly inside a box add up to 13 + 17 + 9 = 39 and cover eight of its squares, the ninth must be 45 − 39 = 6.
| Squares in the cage | Sum | Only possible digits |
|---|---|---|
| 2 | 3 | 1 + 2 |
| 2 | 4 | 1 + 3 |
| 2 | 16 | 7 + 9 |
| 2 | 17 | 8 + 9 |
| 3 | 6 | 1 + 2 + 3 |
| 3 | 7 | 1 + 2 + 4 |
| 3 | 23 | 6 + 8 + 9 |
| 3 | 24 | 7 + 8 + 9 |
| 4 | 10 | 1 + 2 + 3 + 4 |
| 4 | 30 | 6 + 7 + 8 + 9 |
| 5 | 15 | 1 + 2 + 3 + 4 + 5 |
| 5 | 35 | 5 + 6 + 7 + 8 + 9 |
A cage of 16 in two squares holds a 7 and a 9 in some order; if one of them lies in a row that already has its 9, the other square is the 9. Small cages are more often like this, so easy puzzles start faster; expert ones have bigger cages with many sets each, and the 45 rule does more of the work.
How it works
- Choose a level and press New game.
- Fill each row, column and 3 × 3 box with 1 to 9, so that every dashed cage adds up to its sum without repeating a digit.
- Use the combinations helper, notes and the 45 rule; check or take a hint when stuck.
Frequently asked questions
- What are the rules of killer sudoku?
- The usual sudoku rules — 1 to 9 once in every row, column and box — plus cages: the digits in each dashed cage add up to the small number in its corner, and no digit repeats inside a cage.
- What is the 45 rule?
- Every row, column and box adds up to 45. Add up the cages that lie inside a box and compare with 45 to find the squares that stick out — often the key to a hard killer.
- What does the combinations helper show?
- For the selected cage, every set of different digits that makes its sum — for example 17 in two squares can only be 8 + 9 — with the sets that no longer fit the digits you have already put in that cage crossed out. Rows, columns and boxes are left for you to check.
- Does every puzzle have one solution?
- Yes — each puzzle is checked to have exactly one solution; easy ones may give a few digits to start.
- What changes from easy to expert?
- The size of the cages. Easy puzzles are mostly cages of two and three squares, never five, and may give a few digits to start; medium may give digits too. Hard and expert give none, and expert has the most cages of four and five squares, which have the most ways to make their sums.
- Is anything sent anywhere?
- No. The puzzles are made and played in your browser.