How to play Sudoku
Sudoku is a logic puzzle on a 9×9 grid, divided into nine 3×3 boxes. The goal is simple; the deduction is what makes it fun.
The rule
Fill the grid so that every row, every column and every 3×3 box contains the digits 1 to 9, with no repeats. Some digits are given to start — the rest you deduce. A proper Sudoku has exactly one solution and never requires guessing.
Technique 1: Scanning
Pick a digit and scan rows, columns and boxes where it already appears. Those lines block the digit elsewhere. Often a box will have only one cell left where a given digit can legally go — place it there.
Technique 2: The last empty cell
Whenever a row, column or box has eight cells filled, the ninth is forced — it's simply the missing digit. Always finish off near-complete lines first.
Technique 3: Single candidates
For a tricky cell, list which digits are still legal there given its row, column and box. If only one digit survives, it's forced. This "pencil-mark" approach is the backbone of medium and hard solving.
Technique 4: Naked and hidden pairs
If two cells in the same line can only hold the same two digits, those digits are locked to that pair — remove them as candidates from the rest of the line (a naked pair). Conversely, if two digits can only fit in two cells of a line, those cells must hold them (a hidden pair). Spotting pairs unlocks most hard boards.
Tips
- Start on Easy to drill scanning, then move to Medium and Hard.
- Duplicate numbers are highlighted in red — use that to catch slips early.
- Stuck? The Hint button reveals one correct cell.