Expert Sudoku

Our toughest level. Every grid has as few clues as possible and needs logic beyond the patterns used at Hard — expect a long, satisfying solve.

How to play Expert Sudoku

Fill the 9×9 grid so that every row, every column and every bold-outlined 3×3 box contains each digit from 1 to 9 exactly once.
Some digits are given at the start and cannot be changed. Every puzzle has exactly one solution, and you never need to guess.
Tap a square, then tap a number (or type it). Tap the same number again, or use Erase, to clear it.
Switch on Notes to pencil in small candidate digits. Placing a digit removes it from the notes in the same row, column and box automatically.

Look for swordfish patterns: the X-wing idea stretched across three rows and three columns.
Try following a chain of two-candidate squares: if one choice forces a contradiction, the other must be true.
Take breaks — the puzzle and timer are saved, and fresh eyes often spot the key step.

After creating the grid our solver counts its solutions and only keeps it if there is exactly one.

Expert grids are minimal: removing any further clue would allow a second solution, so every remaining digit matters.