Fewer clues, advanced techniques — only for serious solvers
Hard Sudoku puzzles start with only about 28 pre-filled numbers, compared to 42 in easy mode. This means you'll face large empty regions where simple scanning won't work. You'll need to think multiple steps ahead, use pencil notes extensively, and apply advanced solving techniques to crack these puzzles.
At the hard level, basic elimination isn't enough. You'll need pointing pairs — when a number in a box can only appear in one row or column, eliminating that number from the rest of that row/column. Naked pairs work when two cells in the same unit share the same two candidates, allowing you to remove those candidates from other cells in that unit.
The X-Wing technique is your power tool: if a candidate appears in exactly two cells in two different rows, and those cells share the same two columns, you can eliminate that candidate from all other cells in those columns. Master this, and most hard puzzles become solvable.
If hard Sudoku feels comfortable, try our expert difficulty directly on the main Sudoku page. Expert puzzles drop to just 23 clues and may require techniques like Swordfish and XY-Wing. Or try today's Daily Sudoku for a fresh challenge every day.
Hard Sudoku requires advanced techniques like X-Wing, pointing pairs, and naked/hidden pairs. Pencil notes are essential — you'll need to track multiple candidates per cell and eliminate systematically.
Hard Sudoku puzzles typically have 23-28 given numbers. Our hard puzzles provide around 28 clues, while expert mode drops to around 23.
Experienced solvers typically complete a hard Sudoku in 15-30 minutes. Expert puzzles can take 30-60 minutes or more.