Sudoku Game and Solver: Play Sudoku Online, Free

How to play sudoku: the rules

1. The grid has 9 rows, 9 columns and nine 3 × 3 boxes, 81 cells in all.
2. Each row, each column and each box holds the numbers 1 to 9, each once.
3. Some cells are given. Fill the others; a given number never changes.
4. A good sudoku has one solution, and you reach it by looking, never by guessing.

Easy, medium, hard and expert sudoku

Each puzzle here is made when you press its level, and has one solution. The levels differ in what it takes:

• Easy38 numbers given; each cell is the only number left or the only place left
• Medium31 given; the same two ways, but the cells are harder to see
• Hardabout 26 given; the two ways above are not enough, notes and pairs are needed
• Expert22 to 25 given, as few as the puzzle allows; notes all the way

How the sudoku solver works

It checks your numbers first: two of the same in a row, column or box are shown in red. Then it fills the grid the way a person would, the only number left for a cell or the only place left for a number, and says which at each cell. When no cell is certain, it takes the one with the fewest numbers left and the number the solution needs. It also says when a puzzle has no solution, or more than one.

The history of sudoku

Howard Garns, an architect from Indiana, made the puzzle for Dell Magazines, which printed it in 1979 as Number Place. In 1984 the Japanese publisher Nikoli brought it to Japan, and its founder Maki Kaji named it sudoku, short for "the digits must be single". Wayne Gould, a judge from New Zealand, wrote a program to make the puzzles, and in November 2004 The Times in London started printing them. By 2005 sudoku was in newspapers around the world.