Sudoku Online

About Sudoku Online

Sudoku Online offers a challenging puzzle experience that tests your logic and concentration through a variety of Sudoku grids. The classic game requires filling a 9x9 board so that each row, column, and 3x3 box contains the numbers 1 to 9 without repetition. Players can choose from multiple difficulty levels, from easy to expert, making it suitable for beginners and seasoned solvers alike. Beyond the traditional rules, additional game modes bring new twists, such as requiring unique digits along diagonals or solving sum-based groups, adding depth and variety. Helpful features like note-taking allow players to keep track of possible numbers, especially valuable on tougher puzzles. Whether you prefer solo play or competing through leaderboards, Sudoku Online provides an engaging mental workout for puzzle enthusiasts.

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!