Classic sudoku has one constraint repeated three ways. Variants add or alter a constraint, and because the base puzzle is so tight, even a small change transforms how it solves. Here are the ones you are most likely to meet.
Diagonal sudoku (sudoku X)
The two long diagonals must also contain 1 to 9 with no repeats. Just two extra regions, but they cut across every box and interact with everything, which makes the centre of the grid far more constrained than usual.
Solving change: check the diagonals early and often. Cells on a diagonal frequently resolve first, and the centre cell — which sits on both — is often the single most constrained square on the board.
Jigsaw sudoku (irregular)
The nine three-by-three boxes are replaced by nine irregular shapes of nine cells each. Rows and columns work as normal.
Solving change: scanning gets harder because the shapes do not line up with rows and columns, so cross-hatching loses its neat geometry. On the other hand, the irregular regions often produce very strong locked-candidate deductions, because a region snaking across several rows constrains them all.
Killer sudoku
No clues at all. Instead the grid is divided into cages, each with a target sum, and digits cannot repeat within a cage. Classic rules still apply on top.
Solving change: this is the one variant where arithmetic genuinely matters. Small cages are the way in — a two-cell cage summing to 3 must be 1 and 2; one summing to 17 must be 8 and 9. There is also a powerful counting tool: every row, column and box sums to 45, so a set of cages covering most of a region reveals the remainder.
The rule of 45
In killer sudoku, if cages fully cover a row except for one cell, that cell equals 45 minus the cage totals. This single trick opens most killer grids.
Hyper sudoku (windoku)
Four additional three-by-three regions sit inside the grid, offset from the standard boxes. Those overlapping constraints are strong and the puzzles usually need fewer clues as a result.
Samurai sudoku
Five grids overlapping at the corners, sharing boxes. It is not conceptually harder — each grid follows normal rules — but the shared boxes mean progress in one grid unlocks another, and the whole thing takes an hour or more.
Consecutive and greater-than sudoku
Markers between adjacent cells show either that the values are consecutive, or which of the two is larger. These variants reward ordering logic rather than elimination, and they feel quite different from classic solving — closer to a logic puzzle than to sudoku.
Which to try first
| Variant | Difficulty jump | Good if you enjoy |
|---|---|---|
| Diagonal | Small | Classic solving with a twist |
| Hyper | Small | Heavily constrained grids |
| Jigsaw | Moderate | Spatial reasoning |
| Killer | Large | Arithmetic and set logic |
| Samurai | Time, not difficulty | Long sessions |
Diagonal is the natural first step because every technique you know still applies. Killer is the biggest change and the most rewarding if you like the counting side.
What carries over
Every variant still rewards the same core habits: scan before marking, keep candidates accurate, look for regions with few gaps, and never guess. The specific patterns change; the discipline does not. Time spent getting solid at classic sudoku transfers directly.
The board on this site plays classic sudoku with four difficulty levels. If variants become your main interest, the techniques here remain the foundation for all of them.