Solve classic Sudoku or switch to X-Sudoku, Windoku, Killer Sudoku, and Kropki, each adding different constraints to the 9×9 grid.
Here's a quick look at the game:
Sudoku Online by Smartberry expands the standard 9×9 number puzzle with five rule sets. Alongside Classic Sudoku, you can solve X-Sudoku, Windoku, Killer Sudoku, and Kropki puzzles, so the deductions you need to make change depending on the selected mode.
Five Ways to Solve the Grid
The basic objective stays familiar: fill the 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 already filled and act as the clues for the rest of the solution.
Classic mode follows these standard rules and offers Easy, Medium, Hard, and Expert difficulty levels. The four variant modes add another constraint:
- X-Sudoku: digits must also be unique along both main diagonals.
- Windoku: highlighted regions follow the same no-repeat rule as rows, columns, and 3×3 boxes.
- Killer Sudoku: grouped cells must add up to the target sum shown for their cage.
- Kropki: a white dot means two adjacent digits differ by 1, while a black dot means one digit is exactly twice the other.
Because each variant adds information to the grid, those extra markings are part of the deduction process rather than decoration. In Kropki, for example, checking the dot relationship can eliminate candidates that would otherwise satisfy the normal row and column rules.
How to Play Sudoku Online
Click or tap an empty cell to select it, then click or tap a digit to enter that number. When you are not ready to commit to one answer, switch to Notes mode and record several possible digits in the cell.
Start with cells surrounded by the most completed entries. More filled neighbors mean fewer possible digits remain, so these cells are often easier to resolve. Each confirmed number then removes possibilities from its row, column, box, and any additional region or relationship used by the current mode.
Notes become particularly useful on Hard and Expert puzzles because several candidates may remain valid until another part of the grid is solved. Remove candidates as their numbers appear elsewhere in the relevant row, column, box, diagonal, highlighted region, cage, or Kropki relationship.
Every puzzle is designed with one solution that can be reached through logic, so guessing is not required. When progress stops, recheck the existing constraints and look for a cell where only one candidate still satisfies all applicable rules.
