Paused. Take a breath.
Fill every row, column and box with each number exactly once. No guessing needed. Every puzzle has one solution you can reach by logic.
Tap a cell, then a number. Switch on Notes to jot small candidates. On a keyboard use 1–9, arrow keys, Backspace, N for notes, Ctrl+Z to undo and H for a hint.
Tap Hint once to see where to look and why. Tap again to reveal the number.
Beginner and Easy need only single-number logic. Medium adds locked candidates and pairs, Hard adds hidden sets and triples, Expert uses X-Wing and XY-Wing patterns, and Master goes beyond them.