Rules and controls
Fill a 9×9 Sudoku grid with digits 1–9, without repeating a digit in any row, column or 3×3 box. Select an empty cell or one you filled, then use a number button or number key. Given digits cannot be changed. Use Erase or Delete/Backspace to clear an entry. Fill every cell while satisfying all three constraints to finish.
A worked example
A row containing 1, 2, 3, 4, 5, 6, 7, 8 and one blank is missing 9. Check that the blank’s column and 3×3 box also allow 9 before entering it.
Beginner tips
Start with nearly complete rows, columns or boxes. Eliminate candidates using all three constraints. A red conflict marks a repeated digit nearby; it is not a hint revealing the solution.
Choose a difficulty
Every level uses 9×9. The generator aims to remove 30 digits on easy, 40 on medium and 50 on hard while keeping one solution. It may remove fewer to preserve uniqueness; the count alone does not guarantee a solving difficulty.
Questions and answers
Are wrong entries blocked?
No. Repeated digits in a row, column or box are highlighted as conflicts, and you can edit or erase them. Completion requires every cell to satisfy the rules.
Can I come back to a puzzle I started?
Yes. Progress is saved in this browser, so open the same puzzle at the same site address on the same device and browser to continue. Clearing site data or changing device, browser or domain means the existing record will not carry over.
How can I enjoy the daily challenge and practice?
The daily challenge gives everyone the same puzzle for a matching game, UTC date and level. Choose “New practice” to play another practice round at your own pace. The same round repeats its puzzle; different rounds can occasionally have the same layout.