The rules of Sudoko
Sudoko is played on a grid of 9 rows and 9 columns, split into nine boxes of 3 × 3 cells. Some digits are given at the start, and they are fixed. Your goal is to fill every empty cell.
- Each row contains the digits 1 to 9, once each.
- Each column contains the digits 1 to 9, once each.
- Each box of 3 × 3 cells contains the digits 1 to 9, once each.
Every grid has a single solution, checked by a solver before it is published. It can be solved by deduction, without any guessing.
The daily grid
A new grid comes out every day, the same for all players. Its difficulty depends on how many digits are given: around 36 for an easy grid, 28 for a medium one and 22 for a hard one. Sunday's grid is always hard; on weekdays the level changes from day to day.
Controls
Tap an empty cell to select it, then a digit on the keypad below the grid. On a computer, type 1 to 9 directly and move with the arrow keys.
Every digit is checked straight away:
- a correct digit locks in with a small animation, and a wave runs through the row, column or box you just completed;
- a wrong digit turns red, crossed out, and locks the grid: only the undo button stays active so you can remove it.
The keypad shows how many copies of each digit are left to place, and a check mark once a digit is complete. The game controls carry French labels: Annuler (undo), Notes, Effacer (erase) and Joker.
Notes mode
Turn on Notes (or press N) to pencil candidates into a cell. The game refuses an impossible note, meaning a digit already present in the row, column or box, and flashes the cells that block it. When you place a correct digit, it disappears from the notes in its row, column and box.
To note a digit in several cells, drag your finger across the empty cells, then tap the digit. On a computer, Shift + click or Shift + drag works too. Effacer clears the notes of the selected cells. Notes stay on your device.
Locking a digit
A long press on a keypad digit (or the L key) locks it: every copy is highlighted, and each empty cell you tap receives that digit. The lock lifts once all nine copies are placed.
A box solved step by step
Take the top-left box (rows 1 to 3, columns 1 to 3). Dots mark empty cells:
| Col. 1 | Col. 2 | Col. 3 |
|---|---|---|
| 4 | · | · |
| · | 2 | 8 |
| · | 5 | · |
The digits 1, 3, 6, 7 and 9 are missing. Elsewhere on the grid, rows 1 and 3 each contain a 7, column 1 contains a 1 and a 9, and row 3 contains a 6.
1. Place the 7. The box's 7 can be neither in row 1 nor in row 3, which already have one. So it is in row 2, where only one cell is free: column 1. This is a "hidden single": the digit has only one possible spot in the box.
2. The bottom-left cell. It can still take 1, 3, 6 or 9. Column 1 rules out 1 and 9, row 3 rules out 6. Only 3 is possible: this is a "naked single", a cell with just one candidate left.
These two lines of reasoning, finding the spot for a digit or the digit for a cell, solve most easy and medium grids. More advanced techniques are covered in our guide to sudoku solving techniques.
How scoring works
Your score out of 1000 depends on mistakes, jokers and time. On a 9 × 9 grid a mistake costs about 10 points: not much, but they add up.
The Joker reveals the digit of the selected cell if it is empty, otherwise another open cell. Jokers are unlimited and cost about 60 points each. The reference time is 5 minutes on easy, 8 on medium and 12 on hard; finishing twice as fast earns the maximum 20% bonus.
What next?
To become more consistent, read our Sudoko tips. For a shorter version, try Sudolito, SIWA's 6 × 6 sudoku.