About Sudoku
Sudoku asks one thing of you: fill the grid so that every row, every column and every three-by-three box contains the digits one to nine exactly once. There is no arithmetic and no luck. Every puzzle here is generated with exactly one solution and can be solved by logic alone, which means if you find yourself guessing, there is a deduction on the board you have not spotted yet.
Three difficulties are available. Easy leaves enough given digits that scanning alone will carry you through. Medium requires you to start eliminating candidates properly. Hard withholds enough that you will need pencil marks and pattern recognition. Your fastest clear is saved separately for each level.
How to play
- Click a cell to select it, then type a digit from 1 to 9. Backspace or Delete clears it.
- Use the arrow keys to move around the grid without the mouse.
- Turn on Notes to place small pencil marks instead of an answer — the standard way to track candidates.
- Cells that conflict with another cell in the same row, column or box are flagged immediately.
- Fill every cell correctly to finish. The timer stops automatically.
Five tips that actually move your score
- Scan for the last one first. Any row, column or box already holding eight digits hands you the ninth for free. Sweep the whole grid for those before doing anything cleverer.
- Use cross-hatching on a single digit. Pick one number, then walk the nine boxes asking where it can possibly go. Rows and columns that already contain it eliminate whole lines at a time.
- Pencil marks are not optional on Hard. Writing candidates into every empty cell feels slow, but it is what turns a hard grid from guesswork into a chain of forced moves.
- Look for naked pairs. Two cells in the same unit holding the same two candidates mean no other cell in that unit can use either digit. It is the single most useful intermediate technique.
- Never guess. These puzzles always have a logical next step. If you cannot find one, go back and re-scan — a guess that turns out wrong costs more time than the deduction would have.
Frequently asked questions
Is every puzzle solvable without guessing?
Yes. Each grid is generated and then verified to have exactly one solution, so pure logic always suffices.
What do the three difficulties change?
How many digits are given at the start, and therefore which techniques you need. Easy is scan-only, Medium needs candidate elimination, Hard needs pencil marks and pairs.
Are the puzzles the same every time?
No, a new grid is generated for every game, so nothing is memorisable.
Can I check whether I have made a mistake?
Conflicting cells are highlighted as soon as they appear, so a wrong digit shows up the moment it clashes with something.