Windoku Rules: How to Play the Extra-Window Sudoku Variant

Windoku is a Sudoku variant that keeps all the normal Sudoku rules and adds four shaded 3×3 windows inside the grid. If you already know classic Sudoku, Windoku feels familiar right away, but the extra windows change how candidates move and create new solving opportunities.

Quick answer: in Windoku, every row, every column, every regular 3×3 box, and each shaded window must contain the digits 1 through 9 exactly once. Solve it like classic Sudoku, but always check the extra windows before you place a number or remove a candidate.

What Is Windoku?

Windoku is sometimes described as an extra-region Sudoku. The puzzle uses a normal 9×9 Sudoku grid, but four additional 3×3 regions are marked inside the board. Those extra regions act like extra boxes, so the digits 1 to 9 must appear once each in every window.

You can think of it as classic Sudoku plus one more layer of constraints. That extra layer usually makes the puzzle more interesting, not just harder, because numbers can be forced by the windows even when a normal row, column, or box still looks open.

Windoku Rules

1. Standard Sudoku rules still apply

Each row must contain the digits 1 through 9 exactly once.

Each column must contain the digits 1 through 9 exactly once.

Each regular 3×3 box must contain the digits 1 through 9 exactly once.

2. Each shaded window must also contain 1 through 9

The four highlighted windows behave like extra 3×3 regions. That means no digit can repeat inside a window, and every window must end up with all nine digits.

3. A digit can still repeat in different windows if the normal rules allow it

The windows are separate regions. A 5 in the top-left window does not block a 5 in a different window unless they also share a row, column, regular box, or that same window.

How Windoku Differs From Classic Sudoku

In classic Sudoku, you only track rows, columns, and boxes. In Windoku, you also track the four shaded windows. That means a cell can belong to:

• one row
• one column
• one regular 3×3 box
• and sometimes one extra window

This gives you more restrictions and more ways to make logical eliminations. A candidate that looks legal in classic Sudoku may be impossible in Windoku because that digit is already used inside the window.

How to Solve Windoku Step by Step

Start with normal Sudoku scanning

Look for obvious singles, nearly complete rows, nearly complete columns, and standard box deductions. Many Windoku puzzles open with the same basic moves you would use in a regular grid.

Then scan every shaded window like it is another box

This is the most important Windoku habit. Treat each window exactly the way you would treat a 3×3 box. Ask:

• Which digits are missing from this window?
• Which cells in the window can still take each missing digit?
• Does the row or column block some of those spots?

That simple check often reveals a hidden single that you would miss in classic Sudoku.

Use overlap logic

A Windoku cell often sits at the intersection of several constraints. Suppose a cell is inside a row, a column, a regular box, and a shaded window. If any one of those regions already contains a 7, the cell cannot be 7. This makes candidate elimination faster than it first appears.

Keep pencil marks clean

Windoku becomes much easier when your notes stay accurate. If you use pencil marks, update them after every confirmed placement in a window. Stale notes are one of the fastest ways to get stuck in this variant.

Simple Windoku Example

Imagine a shaded window is missing the digits 2, 5, and 8.

• One empty cell already sees a 2 in its row and an 8 in its column, so it must be 5.
• Another empty cell now cannot be 5 because the window already has it, so it becomes 2 or 8.
• A third cell sees an 8 elsewhere in its column, so it must be 2, leaving 8 for the last spot.

That is classic Sudoku logic, but applied to the extra window. Once you make this mental switch, Windoku feels much more approachable.

Best Beginner Tips for Windoku

• Check the windows early. Do not wait until the puzzle gets hard. Many easy placements come directly from the shaded regions.
• Alternate between boxes and windows. After scanning the nine regular boxes, scan the four windows before moving on.
• Write candidates carefully. Windoku adds constraints, so messy notes hurt more than usual.
• Use the extra regions to break ties. If two cells look similar in a row or box, the window rule often separates them.
• Do not overcomplicate it. Windoku is still a logic puzzle, not a guessing puzzle. Start with singles and straightforward eliminations.

Common Windoku Mistakes

Forgetting to scan the windows

The most common mistake is solving it like ordinary Sudoku and ignoring the extra regions for too long.

Treating the windows as decorative

The shaded areas are not visual hints. They are full rules of the puzzle. If a digit repeats in a window, the grid is invalid.

Missing overlap eliminations

A candidate may be blocked by a row, column, box, or window. If you only check two of those four constraints, you will leave impossible numbers in your notes.

Is Windoku the Same as Hyper Sudoku?

Often, yes. Many puzzle sources use Windoku, Hyper Sudoku, or extra-region Sudoku for the same four-window idea. The layout and naming can vary slightly by publisher, but the core rule is the same: the highlighted extra regions must also contain 1 through 9 exactly once.

FAQ

What are the rules of Windoku?

Windoku uses all normal Sudoku rules, plus four shaded 3×3 windows that must each contain the digits 1 through 9 exactly once.

Is Windoku harder than regular Sudoku?

Usually it feels different more than harder. The extra windows add constraints, which can make some placements easier to see even though the puzzle has more rules.

Can you use normal Sudoku techniques in Windoku?

Yes. Singles, hidden singles, pencil marks, locked candidates, and other standard methods still work. You just apply the same logic to the extra windows too.

How should beginners practice Windoku?

Start with easier puzzles and build the habit of scanning the windows after each pass through rows, columns, and boxes. Consistent scanning matters more than advanced techniques.

Conclusion

Once you understand the extra windows, the Windoku rules are straightforward: solve the puzzle like classic Sudoku, but treat each shaded region as another box that must contain 1 through 9. If you scan rows, columns, boxes, and windows in a steady order, Windoku becomes much easier to read.

If you want to build on this variant, continue with Hyper Sudoku rules, review our intermediate Sudoku techniques, or sharpen your note-taking with how to use notes in Sudoku.