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.
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▶ 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.
🎬 On a real grid
The diagrams above isolate the pattern. Here is the same technique on a full grid, at the point where it stalls. Step through it at your own pace.
A real position: unique solution, exact candidates, verified eliminations.
🎮 Put it into practice right away
Four grids from the book are playable online, free and with no sign-up. When you get stuck, the simulator reads your grid and tells you which technique to use, without ever giving the answer away.
Play a grid now →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.
This technique is one of the 6 advanced techniques. See them all in the order to tackle them, split into two families, with the method that makes them automatic.