Sudoku Online — Free puzzle browser game

About Sudoku Online

Sudoku Puzzle is a free online Sudoku game.

No registration, play instantly in your browser. 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. Sudoku Puzzle is also a competitive experience.

Leaderboards track rankings by level, score, and wins. Personal profiles store game history and detailed statistics.

The chat lets players connect, share strategies, and challenge each other.

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!