Sudoku Online

About Sudoku Online

Sudoku Online offers a variety of Sudoku puzzles that challenge your logic and concentration. Players fill a 9x9 grid with digits so that each number appears only once in every row, column, and 3x3 box. The game presents multiple difficulty levels, from beginner-friendly to expert, allowing you to improve at your own pace. Beyond the classic Sudoku format, additional modes introduce unique rules, such as diagonal constraints or sum-based groups, to test different strategies. Each puzzle is logically solvable without guessing, encouraging careful deduction. Features like note-taking help track possibilities as you work through tougher challenges. Sudoku Online also provides competitive elements, including leaderboards and player profiles, enhancing the puzzle experience for those who enjoy friendly rivalry.

How to Play

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!