Hard Sudoku puzzles stop giving you free cells early. You will fill the grid with candidate notes and hunt for naked triples, box-line reductions and X-Wings before the digits start to fall. Expect a thirty-minute solve and a real sense of progress when a single elimination opens up a whole region.
Rated 3.0–4.9 by Sudoku Explainer, hard is where casual solvers become serious ones. Our note mode keeps candidates tidy and removes them automatically when you place a digit. Curious about other grid shapes? See the types of Sudoku overview.