GlobalCore Games
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How to play Sudoku

How to play Sudoku. Fill every empty cell with a digit from 1 to 9. Each row, column and 3×3 box must contain each digit exactly once. The given digits cannot be changed.

Rules

  1. Fill every empty cell with a digit from 1 to 9. Each row, column and 3×3 box must contain each digit exactly once. The given digits cannot be changed.
  2. Select a cell and then a number, or use the keyboard. Notes mark possible candidates without entering an answer. Erase removes your entry; Undo restores a previous move.
  3. Every generated puzzle has one solution. Easy puzzles solve with singles, Medium adds locked candidates and naked pairs, and Hard may require triples or hidden pairs. Difficulty reflects the required logic, not just blank count.
  4. Hints explain a placement or a candidate elimination. Correct conflicting or wrong entries first. Error highlighting can be switched off. There is no time limit or forced loss after mistakes.

A position to try

If a row already contains 1, 2, 3, 4, 6, 7, 8 and 9, its empty cell must be 5. In a naked pair {2,7}, both digits belong to those two cells and leave all other cells in the same unit.

Tap, click or use the keyboard.

Select a cell, then a number. Use Notes for candidates.

Hints explain one step. Undo is always available while history is kept.

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Strategy

Scan a row, column and box together. A number allowed by one row can still be ruled out by the crossing column or box.

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