The goal. Fill every empty square with a number from 1 to 9. Each row, each column and each of the nine 3×3 boxes must hold every number exactly once.
Fill a square. Tap a square, then a number on the pad. The numbers that were there from the start can't be changed.
Mistakes. A number that doesn't belong turns red and counts as a mistake. Tap Erase, or tap another number, to fix it. There is no limit; your mistakes just show at the end.
Notes. Turn on Notes to pencil small numbers into a square while you work it out. Placing a number removes it from the notes in its row, column and box.
Hint. Fills in the selected square, or the easiest open square if none is selected. Hints are counted.
Highlights. The row, column and box of the selected square are shaded, and the same number shows everywhere it is placed. The small count on each number key shows how many are still to place.
Levels. Easy, Medium and Hard start with fewer numbers each step up. The daily puzzle is the same for everyone today; solve it on days in a row to build a streak.
Saved. Your puzzle and time are saved after every move, so Continue picks it up later. The clock stops while a menu is open.
Keyboard: arrow keys move, 1 to 9 fill, Backspace or 0 erases, N switches notes, U undoes, H gives a hint, Esc opens the menu.