Sudoku
How to play
Rows, columns, boxes
A 9×9 grid splits into nine 3×3 boxes. Each row, column, and box must contain 1–9 with no repeats.
Given digits
Bold digits are given. You can’t change or erase them. Your entries are blue.
Notes
Turn on Notes, then tap digits to mark candidates. Faster: press a cell and slide to a number, release to mark; slide to the same number to clear. On desktop, right-click a cell and tap a digit; it closes after one tap. Hold the Notes button to fill every candidate. Related notes clear when you enter a digit.
Keyboard
With a cell selected, 1–9 fill, 0 or Delete erase, arrows move. N toggles notes.
Hints in three steps
The first tap only points at a row, column, or box. “Give me a hint” names the technique. The last tap fills it in. Three hints per game.
Mistakes
A wrong digit counts as a mistake. Five in one game ends it. You can view the solution and start again.
Technique atlas
Hints use these names. Read the diagram, then find it on the board.
Beginner
Naked single
A cell has only one candidate left. That’s the digit.
Medium
Naked pair
Two cells in the same house can only be a and b. Those cells lock a and b; remove them elsewhere.
Medium
Pointing
A digit in a box appears only on one row (or column), so the rest of that row can’t take it.
Hard
Naked triple
Three cells together lock three digits (not every cell needs all three). Remove those digits from the rest of the house.
Hard
X-Wing
A digit in two rows appears only in the same two columns, forming a rectangle. Remove it from the rest of those columns.
Expert
XY-Wing
The pivot is XY, the pincers XZ and YZ. Cells that see both pincers can drop Z.
Expert
Swordfish
A digit in three rows appears only in the same three columns (2 or 3 spots each). Remove it from the rest of those columns.