Sudoku Online

Controls

The goal is to fill a 9×9 grid with digits from 1 to 9 so that each digit appears exactly once in every row, column, and 3×3 box. Some cells are pre-filled — these are your starting clues. Begin with cells that have the most filled neighbors: fewer options make it easier to identify the correct digit. As cells are filled in, the choices for adjacent ones narrow down — the puzzle unfolds as a chain of logical steps. Use the notes mode to write down multiple candidates in a cell and eliminate them as the grid fills up. This is especially useful at Hard and Expert levels. Additional modes come with extra rules. In X-Sudoku, digits must also be unique along both main diagonals. In Windoku, extra highlighted regions apply the same uniqueness rule. In Killer Sudoku, groups of cells must add up to a given sum. In Kropki, markers between cells define relationships: a white dot means the two digits differ by 1, a black dot means one is exactly twice the other. Train your mind!