Windoku 6×6 Medium — Set 81
Solver Notes
Windoku — Free Online & Printable
Windoku, also known as Window Sudoku or NRC Sudoku, adds four fixed 3×3 window regions to the standard 9×9 grid. The windows are positioned symmetrically: top-left at rows 2-4, columns 2-4; top-right at rows 2-4, columns 6-8; bottom-left at rows 6-8, columns 2-4; bottom-right at rows 6-8, columns 6-8. Every window must contain digits 1-9 without repetition, in addition to standard row, column, and box constraints. The overlapping nature of windows and standard boxes creates rich constraint chains that experienced solvers find deeply satisfying.
About the 6×6 Grid
The 6×6 grid strikes a balance between accessibility and depth. With 36 cells in 2×3 boxes, puzzles take 3 to 10 minutes depending on difficulty. The 6×6 is large enough to showcase variant rules meaningfully — Killer cages have room to create genuine arithmetic puzzles, Windoku windows overlap in interesting ways — while remaining completable in a single sitting. Many players find the 6×6 their "daily driver" format: challenging enough to be satisfying, short enough to fit into a break. Variant rules interact more visibly at this size than the 4×4.
Medium Difficulty
Medium difficulty requires applying variant rules in combination with standard sudoku techniques. You will need hidden singles (where a number can only go in one cell within a region, even if multiple numbers are possible for that cell) and basic elimination chains. For Killer Medium, expect some cage combinations where two or more possible sets remain and must be narrowed by row and column logic. Average time: 10-20 minutes for 9×9. Candidate notation is helpful but not essential. This is the recommended starting difficulty for players familiar with standard sudoku.
How to Get Started
- Choose "New Puzzle" to generate a fresh Windoku puzzle with a unique solution
- Click or tap cells to enter numbers (1–6)
- Use the constraint highlights to track which numbers are still available
- Print the puzzle if you prefer solving on paper