You can solve easy Sudokus, but hard puzzles always leave you stuck on the same cells? You pencil in all the candidates and nothing moves forward? X-Wing is very likely the technique you are missing.
The X-Wing is one of the first advanced techniques to master in order to move from intermediate to expert level. In this tutorial, I explain everything: the technique on rows, on columns, the search method, and an application quiz to check your understanding.
How an X-Wing works on rows AND columns (with illustrated examples), the Domino33 method to spot it quickly, and a quiz to validate your knowledge. All in less than 10 minutes of reading.
🎬 The full Domino33 video on X-Wing
Before the written content, here is the 15-minute video where I detail the X-Wing in two parts (rows / columns), the search method, and the final quiz. An English audio track and English subtitles are available (⚙️ icon on the player):
▶ English audio track and English subtitles: pick either from the ⚙️ icon.
Found this video helpful? Over 120 free Sudoku tutorials are waiting on the channel.
▶ Subscribe for freeThe article below follows the same structure as the video so you can learn in your preferred way (reading, video, or both).
Part 1
Row X-Wing & Column X-Wing
What is an X-Wing?
An X-Wing is a candidate elimination technique based on a rectangular pattern. When 4 cells in a grid form a perfect rectangle and all contain the same digit as a candidate (and only in these 4 cells for the 2 rows (or columns) involved) you can eliminate this candidate from the other cells in the columns (or rows) of the rectangle.
The name "X-Wing" comes from the shape drawn by the diagonals connecting the 4 cells: a capital X. The technique exists in two orientations: row X-Wing and column X-Wing.
1️⃣ Row X-Wing (example)
We talk about row X-Wing when we spot the pattern on two rows of the grid. Here is a concrete example with the digit 4 on rows 2 and 6:
The 4 cells circled in red form the X-Wing. The crossed-out "4"s are the candidates to eliminate in columns 3 and 7.
Reading the diagram:
- On row 2, the 4 is only a candidate in columns 3 and 7
- On row 6, the 4 is also only a candidate in columns 3 and 7
- The 4 cells (R2C3, R2C7, R6C3, R6C7) form a perfect rectangle
Logic: the 4 will be placed either at R2C3 + R6C7 (diagonal 1), or at R2C7 + R6C3 (diagonal 2). In both cases, the 4 will occupy one cell in each column of the rectangle. So we can eliminate all other 4 candidates in columns 3 and 7 : here at R4C3, R4C7, R8C3 and R8C7.
2️⃣ Column X-Wing (example)
The column X-Wing is the "rotated 90°" version: the pattern is spotted on two columns and allows elimination in the rows of the rectangle.
The logic is exactly the same. If you understand row X-Wing, you automatically understand column X-Wing. Just swap the roles of rows and columns.
Concretely: on 2 columns, the same digit has only 2 candidate cells, located on the same 2 rows. We get a rectangle, and we can eliminate this digit from all other cells in the 2 rows of the rectangle.
In my video, I show both orientations with different grids so you can clearly see the visual difference between the two.
Part 2
The X-Wing search method
Now that you know what an X-Wing is, you still need to know how to spot it quickly in a grid. Here is the Domino33 method in 4 steps:
Step 1, Choose a digit to analyze
No need to search everywhere at once: your brain will get lost. Focus on one digit at a time (the 1, then the 2, etc.). Do this for each digit still to be placed in the grid.
Step 2, Spot the "binary" rows for this digit
A row is called "binary" for a digit when this digit has only 2 candidate cells left on this row (no more, no less). This is the only configuration that can produce an X-Wing.
Step 3, Look for a second aligned binary row
Once a binary row is found, scan the rest of the grid to find another row where this same digit is a candidate in exactly the same two columns. If you find it: you have a row X-Wing.
Step 4, Repeat the work on columns
Once the rows are scanned, repeat the same search on the columns. Many beginners miss an X-Wing because they only think of one orientation.
Many confuse X-Wing with a simple naked pair. Crucial difference: in an X-Wing, the 2 cells of a row are not a closed pair, they can contain other candidates. What matters is that the studied digit is only a candidate in these 2 columns for the 2 rows involved.
🎬 See the method in action
In the video, I walk through the method on a real grid step by step. It is even clearer than in writing. English audio track and subtitles available.
Exercise
Your turn
Here is a map of the possible locations of the 5. It contains an X-Wing.
Look for two rows whose 5s fall in the same two columns.
Part 3
Application quiz
Now that you have seen everything (theory, row and column examples, and the search method) it is time to put it all into practice. Here is a mini-quiz to check your knowledge. Good luck!
❓ Frequently asked questions
Row X-Wing is spotted on 2 rows and allows elimination in the 2 columns of the rectangle. Column X-Wing is spotted on 2 columns and allows elimination in the 2 rows of the rectangle. The logic is identical, only the reading direction changes. Get used to searching in both orientations.
X-Wing typically appears in puzzles of level 6 and above (hard to expert). On easier puzzles, basic techniques (Naked Pairs, Hidden Pairs, Box Reduction) are enough to progress.
X-Wing is the first step in a family of techniques. Next comes Swordfish (3 rows × 3 columns) and Jellyfish (4 × 4). The logic is the same, but extended to more cells.
No. X-Wing strictly relies on row/column alignment. For blocks, we use the Box Reduction and Pointing Pairs techniques instead.
📋 In summary
X-Wing essentials
- Setup: 4 cells in a perfect rectangle, candidates for the same digit
- Prerequisite: this digit appears only in these 4 cells for the 2 rows (or columns)
- Row X-Wing action: eliminate this digit from all other cells in the 2 columns
- Column X-Wing action: eliminate this digit from all other cells in the 2 rows
- Appears at level: 6+ puzzles (hard to expert)
- Sister techniques: Swordfish (3×3), Jellyfish (4×4)
As with cycling, it is through practice that you become able to spot X-Wings in seconds. To practice, download free level 6+ puzzles from the Domino33 site or subscribe to the channel to discover other advanced techniques.
📘 Go further with the Domino33 books
Every technique on this site is covered step by step in the Domino33 memento, available in English, with the Sudoku Solver Pro software included.
