Sudoku is a logic-based number puzzle played on a 9×9 grid divided into nine 3×3 boxes. Some cells are pre-filled with numbers from 1 to 9. Your task is to fill in the remaining cells so that every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once.

Click or tap an empty cell to select it, then enter a number from 1 to 9. Use logic and elimination — look at which numbers are already present in a row, column, and box to determine what can go where. Start with the rows, columns, or boxes that have the most numbers filled in.

Common techniques include scanning (checking rows and columns for missing numbers), naked pairs (two cells in a group that can only contain the same two numbers), and hidden singles (a number that can only go in one cell within a row, column, or box).

No guessing is needed — every Sudoku puzzle has exactly one solution that can be found through logic alone. This free online version features multiple difficulty levels and highlights conflicts to help you learn.