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.

Advanced: pointing pairs and box/line reduction

When a digit's only candidates inside a box all sit on one row or column, that digit must come from that box — so you can erase it from the rest of that row or column outside the box (a pointing pair/triple). The complementary move, box/line reduction, removes candidates inside a box when a digit in a line is confined to that box. Together these two moves crack open most Hard puzzles without any guesswork.

Common mistakes

• Guessing. A proper Sudoku never needs it. If you feel the urge to guess, there's almost always a logical step you've missed — recount the candidates for the emptiest box.
• Forgetting the box. Beginners scan rows and columns but overlook the 3×3 box constraint, which is often where the decisive elimination hides.
• Stale pencil marks. Every placement removes candidates elsewhere; old marks lead to false "single candidate" conclusions.

Difficulty and the daily puzzle

This Sudoku offers Easy, Medium and Hard boards plus a Daily Challenge that gives everyone the same puzzle each day. Every board is generated to have exactly one solution that's reachable by logic alone, so higher difficulties simply demand deeper techniques (pairs, pointing, box/line reduction) rather than luck.

Frequently asked questions

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