Hard sudoku starts with the fewest givens in our 9×9 set. Early moves are not obvious singles — you will use elimination patterns like naked pairs and pointing pairs.
Still no guessing: if you feel forced to gamble, re-scan for a constraint you missed.
How to play Sudoku Hard
- Standard 9×9 sudoku: unique digits in every row, column, and 3×3 box.
- Givens are minimal — expect to reason about multiple candidates per cell.
- Use New game for another puzzle anytime.
Strategy tips
- Pointing pairs: if a digit’s candidates in a box all lie in one row, eliminate that digit from the rest of that row outside the box.
- Naked triples: three cells in a unit sharing three digits among them lock those digits out of other cells in the unit.
- Avoid filling a cell until only one candidate remains unless you are sure — a wrong digit cascades fast on hard grids.
- Crosshatch: pick a digit and scan which rows and columns already contain it to see where it must go in a box.
- Step down to medium if a puzzle stalls you for ten minutes — building technique beats brute force.
Common questions
Do I need advanced sudoku notation for hard?
Not on paper, but thinking in candidates helps. The techniques named above are enough for our hard puzzles without X-Wings or coloring.
