Click a cell, then a number 1–9. Keyboard: arrows to move, 1–9 to fill, Backspace to erase.
About Sudoku
Free sudoku online — the classic 9×9 number puzzle, no signup or installation required. Fill the grid so every row, every column, and every 3×3 box contains the digits 1–9 exactly once. Four difficulty levels cover newcomers through experts, with a running solve timer if you want to race yourself.
Mistakes are highlighted but never punished — undo and try again whenever. Pondernook sudoku is designed for clean five-to-fifteen minute sessions in any browser; pencil-mark notes are supported. Hard puzzles include techniques like hidden pairs and X-wings; easy puzzles solve with naked singles alone. No daily-streak pressure, no ads in your peripheral vision — just the puzzle and the keyboard.
Frequently asked questions
What do the difficulty levels change?
They change how many digits are given and which solving techniques are needed. Easy puzzles fall to simple scanning, while Hard and Expert require methods like hidden pairs and X-wings.
Can I make pencil-mark notes?
Yes. Notes are supported, so you can jot candidate digits into a cell before committing to a final answer.
Are mistakes penalised?
No. Wrong entries are highlighted but never end the game — erase and try again. A solve timer runs if you want to race yourself.