Variants & sizes
Same logic, new units — and boards from 6×6 to 16×16.
Variants & sizes
Every technique above still applies in the variants — they just add or reshape the units you check.
X-Sudoku
Classic rules plus both main diagonals must each contain 1–9. The diagonals are two extra units to scan for singles, pairs, and pointing logic. More about X-Sudoku →
The two diagonals (highlighted) behave like extra rows: a digit already on a diagonal can't repeat anywhere else on it.
Jigsaw
Nine irregular connected regions replace the 3×3 boxes. The logic is identical — each region still needs 1–9 exactly once — but the shapes change which cells "see" each other. More about Jigsaw →
Each coloured region must contain 1–9 once, just like a box — but the region's odd shape changes which cells share a unit.
Killer
Dashed cages with target sums replace given digits. On top of classic rules, the cells in a cage must add up to the target with no repeats — so cage-sum combinations become a technique of their own (a 3-cell cage summing to 7 can only be 1+2+4). More about Killer →
A 3-cell cage summing to 7 can only be {1, 2, 4} — so 3, 5, 6, 7, 8, 9 are removed from every cell in the cage.
Board sizes
Stillgrid plays at more than one size:
- 6×6 — 2×3 boxes, digits 1–6. A gentle introduction; the same row/column/box logic on a smaller board.
- 9×9 — the classic board everything above is taught on.
- 16×16 — 4×4 boxes, digits shown as 1–9 then A–G. Much larger; best on a bigger screen. Currently available for Classic and X-Sudoku.
Common questions
How is sudoku difficulty graded on Stillgrid?
Stillgrid grades each puzzle by the hardest solving technique it actually requires, not by clue count. You can choose Easy, which solves with naked and hidden singles; Medium, which needs pairs and pointing; or Nightmare, which needs advanced patterns like X-Wing, Swordfish, XY-Wing, or chains.
Is Stillgrid free?
Yes. Every puzzle, variant, and size is free to play, with no signup needed to start a puzzle.