Sudoku Online: game overview
- Category
- Puzzle
- Play
- Online in your browser
About Sudoku Online
Fill a Sudoku grid using logic and the standard number-placement rules. Choose from four difficulty levels and work through the puzzle at your own pace.
The classic mode offers four difficulty levels: Easy for beginners, Medium for steady practice, Hard for experienced players, and Expert for those who seek a real challenge. Additional game modes expand the standard rules: X-Sudoku adds diagonal constraints, Windoku introduces extra regions on the grid, Killer Sudoku requires groups of cells to meet a target sum, and Kropki adds ratio and difference markers between adjacent cells.
Every puzzle has exactly one solution, reachable through pure logic — no guessing required. If you get stuck, a step was missed somewhere, and it can always be traced back.
Game highlights
- Puzzle
How to play Sudoku Online
- 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!
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!
Tips for your next attempt
- Look for rows, columns or boxes with few missing numbers, and eliminate candidates before guessing.
