Hyper Sudoku — play the four-windows variant free online

Also known as Windoku or NRC sudoku: classic rules plus four extra shaded 3×3 windows that must each contain 1–9. 400,000 puzzles, every one verified for a unique solution.

How Hyper Sudoku works

The standard rules hold — rows, columns and the nine 3×3 boxes each take 1–9 once. Hyper adds four more 3×3 regions, shaded on the grid and offset from the main boxes, that must also contain 1–9. That's thirteen box-shaped constraints woven through one grid, and because the windows overlap four main boxes each, information propagates in ways classic sudoku never allows.

The hidden fifth window

Here's the trick that unlocks Hyper: the cells not covered by any window (plus the centre-edge cells) form their own forced patterns. Because the four windows contain 36 cells holding four full sets of 1–9, arithmetic on the remaining cells yields eliminations the grid never states explicitly. Spotting these "phantom regions" is the variant's signature move.

Four difficulties

• Hyper Easy — 38 givens. The windows do half the scanning for you.
• Hyper Medium — 31 givens. Thirteen boxes to keep satisfied.
• Hyper Hard — 26 givens on a very crowded grid.
• Hyper Expert — 23 givens. The windows are your only friends.

Permanent shareable puzzle numbers, automatic progress saving, print-ready grids with the windows shaded, and dark mode — same as every game on the site.

More variants

Prefer diagonals to windows? Sudoku X is next door. New to the game entirely? Start with classic sudoku and its beginner-proof Coward's mode. And the site's main event remains killer sudoku, now running all the way up to Nightmare difficulty.