What Is an X-Wing?
An X-Wing is a pattern where a specific candidate number appears in exactly two cells in each of two different rows, and those cells line up in the same two columns. When this happens, you know the number must go in two of those four cells (diagonally), which means you can eliminate that candidate from all other cells in those two columns.
The same logic works in reverse: two columns with the candidate in exactly two cells each, lining up in the same two rows. Then you eliminate from the rows instead.
The name "X-Wing" comes from the shape — if you draw lines connecting the four cells, they form an X.
When to Look for It
X-Wing is an intermediate-to-advanced technique. You typically need it on hard and expert puzzles, and only after basic techniques (scanning, singles, pairs) have stalled.
Look for X-Wing when you notice a candidate number that stubbornly appears in exactly two positions across multiple rows (or columns). If two of those rows share the same column positions, you have a potential X-Wing.
You need pencil marks filled in for the relevant area of the grid. Without candidates written down, X-Wing patterns are nearly impossible to spot.
Step by Step: Spotting a Row-Based X-Wing
Step 1: Pick a candidate number (say, 7). Scan each row and note which rows have the candidate 7 in exactly two cells.
Step 2: Compare those rows. Do any two of them have the candidate 7 in the same two columns? If yes, you have found an X-Wing for the number 7.
Step 3: The elimination — remove the candidate 7 from all other cells in those two columns (except the four X-Wing cells themselves).
The column-based version is the mirror: find two columns where a candidate appears in exactly two cells, check if they share the same two rows, and eliminate from those rows.
Worked Example
Suppose you are looking at the candidate 3 across the grid. You notice:
In Row 2, the candidate 3 appears only in Column 4 and Column 8.
In Row 7, the candidate 3 also appears only in Column 4 and Column 8.
This forms an X-Wing. The four cells are: R2C4, R2C8, R7C4, R7C8. The number 3 must end up in exactly two of these cells — either R2C4 and R7C8, or R2C8 and R7C4.
Either way, Column 4 and Column 8 are each "claimed" by one of these placements. So you can safely remove the candidate 3 from every other cell in Column 4 and Column 8.
For instance, if R5C4 also had 3 as a candidate, you would erase it. That elimination might reduce R5C4 to a single candidate, giving you a new placement.
Quick Checklist for Spotting X-Wing
1. Choose a candidate number.
2. Find rows (or columns) where that candidate appears in exactly 2 cells.
3. Check if two such rows share the same two columns (or vice versa).
4. If yes: eliminate the candidate from other cells in those columns (or rows).
Is This Really an X-Wing? Three Validation Tests
Test 1: The candidate appears in exactly two cells in each of the two rows. Not three, not one — exactly two.
Test 2: The column positions match. Row A has the candidate in columns 4 and 8, and Row B also has it in columns 4 and 8. If the columns differ, it is not an X-Wing.
Test 3: The elimination only removes candidates from other cells in the shared columns (or rows). You never remove the candidate from the four X-Wing cells themselves.
Common Mistakes
Miscounting candidates. If a row has the candidate in three cells instead of two, it is not an X-Wing. Double-check your pencil marks.
Columns do not align. The two rows must share exactly the same two columns. A near-miss (columns 4 and 8 in one row, columns 4 and 7 in another) does not count.
Eliminating from the wrong axis. In a row-based X-Wing, you eliminate from columns. In a column-based X-Wing, you eliminate from rows. Mixing this up will break your solve.
Removing candidates from the X-Wing cells. The four pattern cells are protected. Only other cells in the affected columns (or rows) lose the candidate.
Stale pencil marks. If your candidates are not up to date, you might see a false X-Wing. Always update pencil marks before looking for advanced patterns.
Trying X-Wing too early. If you have not exhausted singles, pairs, and pointing/claiming, you are making things harder than they need to be. X-Wing is a cleanup technique for when basic methods stall.
Practice Suggestions
X-Wing patterns appear most often in hard and expert puzzles. Try these to build pattern recognition:
Play our Deluxe Player on Hard or Expert with the mistake toggle on. This lets you experiment with eliminations safely.
Print a hard puzzle pack or expert puzzle pack and solve on paper with a pencil. Paper solving forces you to maintain candidates carefully, which is where X-Wing spotting happens.
Frequently Asked Questions
How common are X-Wing patterns?
They appear in most hard and expert puzzles, though not every puzzle requires one. The technique becomes more useful as difficulty increases.
What is the difference between X-Wing and Swordfish?
X-Wing uses two rows and two columns (a 2×2 pattern). Swordfish extends this to three rows and three columns (a 3×3 pattern). The logic is the same, just larger.
Can I solve hard puzzles without X-Wing?
Sometimes, yes. Other techniques like naked pairs, hidden pairs, and box-line reduction might be enough. But knowing X-Wing gives you another tool when those are not sufficient.
Do I need to check all 9 numbers for X-Wing?
In theory, yes. In practice, focus on numbers that have many placements already (6 or 7 of 9 placed). The remaining candidates are more likely to form patterns with few cells.