What is an X-Wing in sudoku?

An X-Wing is a candidate-elimination pattern. When a digit appears in exactly two cells of one row and exactly two cells of another row, and those four cells line up in the same two columns, they form a rectangle. The digit must sit on one diagonal of that rectangle, so it can be removed from every other cell in those two columns. The same works with rows and columns swapped.

How do I find an X-Wing quickly?

Pick one candidate digit and scan for rows where it has exactly two possible cells. If two such rows put that digit in the same pair of columns, you have an X-Wing and can eliminate the digit from the rest of those columns. Then repeat the scan by columns. Doing it digit-by-digit is far faster than staring at the whole grid.

Is the X-Wing worth learning for speed?

For completeness, yes — it's the first pattern that unblocks a genuinely hard puzzle. For everyday speed, it's low priority: X-Wings are rare and expensive to spot, so time is better spent making singles and pairs instant. Treat 'this puzzle needs an X-Wing' mainly as a difficulty signal.

Difficulty tier T3

X-Wing Sudoku Technique: How to Spot It Fast

The X-Wing is usually the first "advanced" technique a solver learns, and it looks more intimidating than it is. It's a single-digit pattern that tells you where a number can't go. Here's how to see it in seconds — and an honest take on when it's worth looking for.

What an X-Wing actually is

Pick one digit — say 4. An X-Wing forms when that digit has exactly two possible cells in one row, exactly two in another row, and all four cells sit in the same two columns. Those four cells make the corners of a rectangle.

Because the 4 has to appear once in each of those rows, and only in those two columns, the two 4s must sit on one diagonal of the rectangle or the other. Either way, each of the two columns gets its 4 from inside the rectangle. So the 4 can be eliminated from every other cell in those two columns. The pattern works identically if you swap the words "row" and "column."

It doesn't place a digit. Like all the tier-2 and tier-3 techniques, it clears candidates so the next hidden single can appear.

How to find one fast

Don't scan the whole grid at once. Go one digit at a time:

Take a candidate digit and find every row where it has only two possible cells.
Check whether any two of those rows place the digit in the same pair of columns.
If they do, that's an X-Wing — eliminate the digit from the rest of those two columns.
Repeat the same scan looking down columns instead of across rows.

Working digit-by-digit turns a vague hunt into a quick, mechanical check.

Speed note: an X-Wing sits at tier T3 in Speedoku's difficulty model — the level where singles-clicking stops working. That's the useful signal. If a puzzle forces an X-Wing, it's genuinely hard by construction, not just tedious. Most puzzles you solve against the clock never require one.

When to bother

Be honest about the trade. X-Wings are rare and slow to spot, so hunting for one on an easy or medium grid is wasted time — the cheapest available move is almost always a single or a pair you skipped. Learn the X-Wing so a hard puzzle can't stop you cold, then keep your eyes on the cheap moves for everyday speed.

The fastest way to internalize the pattern is reps: solve enough hard boards and the rectangle starts to jump out. Practice free or take today's Daily Challenge — one shared board, one attempt.

Frequently asked questions

What is an X-Wing in sudoku?: An X-Wing is a candidate-elimination pattern. When a digit appears in exactly two cells of one row and exactly two cells of another row, and those four cells line up in the same two columns, they form a rectangle. The digit must sit on one diagonal of that rectangle, so it can be removed from every other cell in those two columns. The same works with rows and columns swapped.
How do I find an X-Wing quickly?: Pick one candidate digit and scan for rows where it has exactly two possible cells. If two such rows put that digit in the same pair of columns, you have an X-Wing and can eliminate the digit from the rest of those columns. Then repeat the scan by columns. Doing it digit-by-digit is far faster than staring at the whole grid.
Is the X-Wing worth learning for speed?: For completeness, yes — it's the first pattern that unblocks a genuinely hard puzzle. For everyday speed, it's low priority: X-Wings are rare and expensive to spot, so time is better spent making singles and pairs instant. Treat 'this puzzle needs an X-Wing' mainly as a difficulty signal.