About the game
Sudoku Online drops you onto a 9×9 board with a handful of numbers already placed. Your job is to complete it so that 1 through 9 each appear a single time in each row, each column and each of the nine 3×3 blocks. Those starting numbers are the only hints you get.
Easy, Medium, Hard and Expert change how crowded the board starts. Four extra modes rewrite the rules: X-Sudoku adds the two long diagonals, Windoku adds highlighted regions, Killer gives cell groups a target sum, and Kropki puts white dots (difference of 1) or black dots (double) between neighbors. Notes mode keeps several candidates in a cell so you can erase them as numbers land. Every grid has one answer and logic alone finds it.
How to play
- Tap or click a cell, then press 1–9 to place a digit.
- No digit repeats in a row, a column or a 3×3 block.
- Start with cells whose row, column and block are already crowded, since fewer choices remain.
- Switch on notes mode to store candidates, and follow the extra rule in X-Sudoku, Windoku, Killer and Kropki grids.