Windoku 6×6 Easy — 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 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.
Easy Difficulty
Easy difficulty is designed so that the variant's unique rule creates clear, immediate deductions. In X-Sudoku Easy, most diagonal cells can be filled using only the diagonal constraint plus row and column logic. Solving technique required: naked singles (cells with only one possible value) and direct constraint elimination. No candidate markup needed. Average time: 3-8 minutes for 9×9, 30-90 seconds for 4×4. If you are new to this variant type, Easy is where you build intuition for the extra rule before encountering combinations of constraints.
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