Windoku 9×9 Medium — Set 21
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 9×9 Grid
The 9×9 grid is the full standard size for all sudoku variants. With 81 cells in 3×3 boxes, a 9×9 variant puzzle takes 10 to 60+ minutes depending on difficulty level and variant type. All variant rules reach their full expressive potential at this size: Killer cages create complex arithmetic networks, Jigsaw regions form visually distinctive shapes, and diagonal constraints span the entire grid. The 9×9 is where experienced solvers spend most of their time, and where the depth and elegance of each variant rule is fully revealed.
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 (1–9)
- Use the constraint highlights to track which numbers are still available
- Print the puzzle if you prefer solving on paper