How do you play Killer Sudoku?
Just like regular sudoku, every row, column and bold 3×3 box holds 1 to 9 exactly once. On top of that, the grid is covered with dotted cages, and the digits in each cage must add up to the number in its top left corner. Almost no digits are given, so the sums are your clues.
Every puzzle here was checked by a solver that understands cage sums to make sure it has exactly one solution. You never need to guess.
What are the rules of Killer Sudoku?
| Rule | What it means |
|---|---|
| Rows, columns, boxes | Each of the 9 rows, 9 columns and 9 boxes contains 1 to 9 once. |
| Cage sums | The digits inside a dotted cage add up to its small corner number. |
| No repeats in a cage | A digit can appear only once in a cage, even when the cage crosses a box border. |
| Given digits | Only Easy starts with 3 to 6 digits filled in. Normal and Hard start from an empty grid. |
What are the best Killer Sudoku strategies?
Start with cages that have only one possible combination, then use the fact that every row, column and box adds up to 45 to work out single cells.
- Look for unique combinations. Two cells adding to 3 must be 1+2, to 4 must be 1+3, to 16 must be 7+9 and to 17 must be 8+9. Three cells adding to 6 are 1+2+3 and to 24 are 7+8+9.
- Use the rule of 45. If the cages inside a box cover all but one cell, or stick out by one cell, the difference from 45 gives you that cell.
- Read the helper line under the grid. Pick a cell and it shows the cage's remaining sum and every combination that still fits.
- Take notes. Writing candidates in each cage lets you combine sum logic with classic tricks like hidden singles and pairs.
What is the difference between Easy, Normal and Hard?
Levels differ in cage size and how many digits are given. Bigger cages allow more combinations, so they are harder to pin down.
| Level | Cages | Given digits |
|---|---|---|
| Easy | 30 to 34, many small ones | 3 to 6 |
| Normal | 25 to 28 | None |
| Hard | 20 to 23, up to 6 cells | None |
Controls
- Enter a digit: tap a cell, then a number button. Tap the same number again to clear it. The small number under each button shows how many are still missing.
- Notes: turn on Notes to pencil in small candidates. Placing a real digit removes it from the notes in the same row, column, box and cage.
- Check: when on, wrong digits turn red. Even when off, repeats and cages with the wrong total are shown in red.
- Keyboard: digits, arrow keys, Backspace, N for notes, Ctrl+Z to undo, H for a hint, E to toggle checking.
- Continue: your grid, notes and time are saved in this browser, and a Continue button appears on the start screen.
The daily puzzle is the same Normal grid for everyone and changes at midnight Korea time. Best times for each level are saved only in this browser.
Where did Killer Sudoku come from?
Killer Sudoku was already a well known sudoku variant in Japan in the 1990s under the name samunamupure, a Japanese take on "sum number place".
It reached most English speaking players in 2005, when The Times in London began printing it as Killer Sudoku. Today it is the puzzle many people try next once regular sudoku feels easy.