What makes a sudoku hard
A hard puzzle runs out of singles at least once. To get going again you need an elimination: a pointing pair (a digit confined to one line inside a box), a naked or hidden pair, or a triple. They don't place a number themselves; they remove candidates until a single appears.
We grade every puzzle by the hardest step it needs, the way sudoku experts do, so every grid on this page really does call for one of these, and none needs more. Our guides show each one on a real board.
Tips for hard puzzles
- Pencil in candidates early. On hard grids the marks are how you find the next move, not a last resort.
- When two cells in a unit share the same two candidates, those digits belong to that pair. Remove them from the rest of the row, column or box.
- Inside each box, check whether a digit sits on just one row or column. If it does, it can be crossed off the rest of that line.
Questions
What is the difference between hard and expert sudoku?
Hard puzzles need pairs, triples and pointing. Expert puzzles need at least one of the bigger patterns, such as an X-Wing, a Swordfish or an XY-Wing.
Why do I get stuck on hard sudoku?
Usually there is a pair or a pointing digit you haven't noticed. Fill in pencil marks for the whole grid (auto-notes does it in one tap) and the pattern tends to jump out. If it still doesn't, the hint button shows the next step and explains it.
Can two people solve a hard sudoku together?
Yes, and it is a good way to take on hard grids, because two people spot different patterns. "Play this with a friend" opens a shared multiplayer room at this level.