Notes on this puzzle
Sudoku #5402 is an expert grid with 28 givens, which leaves 53 cells waiting for a digit. Played purely by logic, it takes 58 forced steps from the first placement to the last.
Most cells fall to the hidden single move: 52 of the 58 steps. Box–line reduction accounts for 3 more. The toughest moment needs X-Wing, and that single step is what sets the level.
Among the givens, 1 is the most common digit (5 times) and 7 the rarest (1). The emptiest box is the top-left one, with 2 givens; the top-middle box is the most crowded, with 4.
Where to beginLook at row 1, column 5 first: a hidden single is available there from the very start. Expect a stage where only a pattern across several lines moves the grid on; full notes make it visible.