Hard Sudoku Online

Puzzles that make you lift your gaze: no longer one cell or one box at a time, but patterns stretching across the whole grid. Free, no sign-up, playable offline. And with one precise guarantee: every puzzle solves all the way through by deduction — never by trial and error.

What changes at the hard level

At the earlier levels, techniques work inside a single unit, or at most along the border between a box and a line. At hard, the logic extends: two distant rows constrain one another, three cells split three candidates between them, a pair of values sets off a short chain. You need your pencil marks in order — and you need to read the grid as a system, not a collection of squares.

The internal solver certifies the tier: a puzzle is hard if it requires at least one technique from this group, and none of those reserved for expert.

The techniques required

Triples (naked and hidden): three cells in a unit sharing three candidates, extending the pair principle. The X-Wing: four cells at the corners of an imaginary rectangle, on two rows that each allow a candidate in only two columns — and that candidate vanishes from the rest of those columns. The XY-Wing: three two-candidate cells linked through a pivot, eliminating a candidate wherever the two branches intersect.

The X-Wing is the signature pattern of the level, and it has a dedicated guide: how to solve an X-Wing.

No guessing — deduction only

An honest hard sudoku never asks you to try a number and see where it leads. Every puzzle at this level has been solved by the solver using only the techniques listed above: if you're stuck, a visible logical step always exists on the grid. Finding it is the game. In that sense, hard isn't easy with fewer clues — it's a different way of looking.

After hard

Once X-Wings and XY-Wings stop hiding from you, one tier remains: expert sudoku, with Swordfish and simple coloring. And if you want to revisit the foundations everything rests on, the technique guides index starts from pairs.