Windoku Sudoku: rules, strategy and how to start
Four extra 3×3 windows behave like additional boxes. Each must contain 1–9 once, and every one of them overlaps four ordinary boxes.
Why the rule changes everything
The windows overlap rows, columns and boxes, so a single digit can be excluded from a cell by eight different units. In the centre of the board, a cell usually belongs to a row, a column, a box and two windows.
That overlap is why windoku puzzles have far fewer givens than a standard puzzle for the same difficulty: the constraint density is roughly double.
How to start a board
- Treat the four windows as four extra rows. Scan one digit at a time across all thirteen units (9 rows, 9 columns, 9 boxes, 4 windows).
- Start with the centre: cells at rows 4–6 and columns 4–6 sit in the most windows.
- Look for a digit that appears in three of the four windows; the fourth window then has very few places left.
Common mistakes
- Forgetting that the windows exist when scanning a row — the row alone is not enough.
- Assuming the four windows tile the board; they overlap and leave five 3×3 blocks outside them.
- Placing a digit that violates a window while satisfying its row, column and box.
Frequently asked questions
Where are the four windows?
The 3×3 blocks anchored at rows/columns 2–4 and 6–8 — the four copies of a 3×3 block inset one cell from each corner.
Is windoku the same as hypersudoku?
Effectively yes. The two names describe the same four-window rule.
Every board on this site is generated with a uniqueness check, so the puzzle in front of you has exactly one solution and every digit can be proved rather than guessed.
Play Windoku Sudoku ↗