How to play Sudoku

What Sudoku is

Sudoku is a number puzzle on a grid of 81 cells, made of nine rows, nine columns and nine 3×3 boxes. Some cells already hold numbers. Your job is to fill in the rest so that every row, every column and every box contains each number from 1 to 9 exactly once. No arithmetic is needed: the numbers are just symbols, and every step can be worked out by logic alone.

Playing Sudoku on AllFun

AllFun Sudoku has four levels: Easy, Medium, Hard and Expert. Every puzzle has exactly one answer, and each is graded by the techniques a person needs to solve it, not just by how many numbers are given. The Daily puzzle is the same for everyone: Easy on Monday, Medium on Tuesday, Wednesday and Friday, Hard on Thursday and Saturday, and Expert on Sunday. Solve it for a crown and keep a streak going. Tips for each level: easy, hard and expert sudoku.

Tap a cell, then a number. Or tap a number first to hold it, then tap cells to drop it in; every cell with that number lights up, so gaps are easy to spot. Turn on Notes to pencil in small candidates. A hint fills one cell and says why, with three free each puzzle, and Undo takes back any move. On a computer you can use the keyboard: arrow keys to move, 1 to 9 to place, Backspace to erase, N for notes and H for a hint.

In Classic mode a wrong number turns red and three mistakes end the game. Relaxed removes the limit, and Off stops checking altogether, so you find your own mistakes. Fewer mistakes and hints earn more stars.

The rules

• Each row must contain the numbers 1 to 9, once each.
• Each column must contain the numbers 1 to 9, once each.
• Each of the nine 3×3 boxes must contain the numbers 1 to 9, once each.
• The numbers given at the start cannot be changed.

A proper Sudoku has a single solution, so you never need to guess. If you find yourself guessing, there is a logical step you have not spotted yet.

Solving techniques, from easy to hard

1. Scan for hidden singles. Pick a number and a box. If that number can go in only one cell of the box, because the others are blocked by the same number in their rows or columns, place it.
2. Find naked singles. Look at one empty cell and rule out every number already in its row, column and box. If only one number is left, it goes there.
3. Pencil in candidates. On Medium and above, write the possible numbers in each cell with Notes. Auto-clear notes removes a number from the notes around a cell as soon as you place it.
4. Use pointing pairs. If, inside one box, a number can only go in cells that share a single row, that number cannot go anywhere else in that row outside the box. The same works for columns.
5. Look for naked pairs. When two cells in a row, column or box can only hold the same two numbers, those numbers belong to those cells, and you can remove them from every other cell in that unit.
6. Try the X-Wing on Expert. If a number fits in exactly two cells in each of two rows, and those cells line up in the same two columns, the number can be removed from the rest of those two columns.

A short history

The modern puzzle was first published in a puzzle magazine in 1979 under the name Number Place. A puzzle publisher later gave it the name Sudoku, short for a phrase meaning that the digits must stay single, and in the mid-2000s it spread to newspapers around the world and became one of the most popular puzzles anywhere.

Sudoku FAQ