How to Play

The rules

Fill every empty cell with a digit from 1 to 9.
Each row must contain every digit from 1–9 exactly once.
Each column must contain every digit from 1–9 exactly once.
Each 3×3 box must contain every digit from 1–9 exactly once.
Pre-filled (dark) numbers are clues — they cannot be changed.

Controls

Click a cell to select it, then tap a number on the pad.
Keyboard: type 1–9 to enter, Delete to erase, arrow keys to navigate.
Click a filled cell to highlight every occurrence of that digit.
Enable Notes to pencil in candidate digits (small numbers).
Hint reveals the correct answer for the selected cell (3 hints per game).

History of Sudoku

The roots of Sudoku reach back to Leonhard Euler's Latin Squares (1783) — mathematical grids where each symbol appears exactly once in every row and column.

Modern Sudoku was created by American architect Howard Garns and first published in 1979 in Dell Pencil Puzzles & Word Games under the name "Number Place".

In 1984 Japanese publisher Nikoli introduced the puzzle as 数独 (Sūdoku), an abbreviation of "Sūji wa dokushin ni kagiru" — "digits must remain single". The grid was slightly refined: symmetry of the given clues and a maximum of 32 clues became part of Nikoli's standard.

In 1997, retired Hong Kong judge Wayne Gould discovered a Sudoku book in a Tokyo bookshop and spent six years writing a computer program to generate puzzles. In November 2004, The Times (London) published his puzzles and sparked a worldwide craze. By 2005 Sudoku had appeared in hundreds of newspapers on every continent.

Tips & Fun Facts

Solving strategies

Naked Single — a cell where only one digit fits given the row, column and box constraints.
Hidden Single — a digit that can only be placed in one cell within a row, column or box.
Start with the row, column or box that already has the most digits filled in.
Use Notes to mark candidates and cross them off as you solve neighbouring cells.
On harder puzzles, look for naked pairs: two cells in the same unit that each contain only the same two candidates.

Did you know?

The total number of valid 9×9 Sudoku grids is 6.67 × 10²¹.
A puzzle needs at least 17 given clues to guarantee a unique solution — proven in 2012.
Sudoku is not a mathematics puzzle: any 9 distinct symbols (letters, shapes, colours) work equally well.
The first World Sudoku Championship was held in Lucca, Italy, in March 2006.
The hardest known puzzle, "AI Escargot" by Arto Inkala, reportedly takes most humans hours to solve.

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