The X-Wing is the first advanced sudoku pattern most solvers learn, and it is the gateway to the wider family of “fish” techniques. It looks intimidating on paper but rests on one simple idea: when a digit is boxed into the same two columns across two rows, those columns are spoken for, and the digit can be cleared from everywhere else in them. This guide builds the pattern up step by step. If you are still placing digits with the basics, read naked and hidden singles first, then the full sudoku techniques overview.
An X-Wing only becomes visible once you keep accurate pencil marks — the small list of candidates in each empty cell. Without them, the pattern hides. So reach for it after singles, pairs, and locked candidates have stalled, not before.
The pattern: a rectangle of four cells
Pick a single digit, say 6. Find two rows in which that digit has exactly two possible cells each, and where both rows place those cells in the same two columns. The four cells form the corners of a rectangle. That rectangle is the X-Wing. The name comes from the two diagonals you can imagine crossing inside it, though the logic uses the corners, not the diagonals.
Here is the key deduction. Each of the two rows must place the 6 in one of its two cells, and both cells sit in the same pair of columns. Whichever way it resolves, one 6 lands in the left column and the other in the right column — the two rows fully occupy those two columns with the digit 6. That means no other cell in either column can be a 6. You erase 6 from every other cell of both columns.
Why the elimination is certain
Consider the two ways the rows can resolve. If the top row’s 6 goes in the left column, the bottom row’s 6 is forced into the right column, because the two rows cannot both use the same column. If instead the top row’s 6 goes in the right column, the bottom row’s 6 is forced left. Either arrangement puts a 6 in each column, so both columns already have their 6 accounted for by these two rows. Any 6 elsewhere in those columns would create a second 6 in a column, which the rules forbid. The elimination follows with no guessing.
Rows and columns are interchangeable
The pattern works just as well with the roles swapped. Find a digit that, in two columns, is limited to the same two rows — again four cells forming a rectangle. Now the two columns lock the digit into those two rows, so you can erase the digit from the other cells of both rows. Whenever you hunt for an X-Wing, check both orientations: two rows fixing two columns, and two columns fixing two rows.
When it helps, and what comes next
An X-Wing rarely places a digit outright. Instead it removes candidates, and those removals often unlock a naked or hidden single elsewhere. Treat it as a tool for breaking a deadlock: when scanning, singles, pairs, and locked candidates all stall, look for a digit confined to two cells in two parallel units. The X-Wing also introduces the logic behind larger fish — the Swordfish uses three rows and three columns on the same principle, and the Jellyfish extends it to four. Learn the X-Wing well and those patterns stop looking mysterious.
Patterns like this become quicker to see with practice on real boards. Try the daily puzzle on Microsoft Sudoku or a fresh daily sudoku, and keep your pencil marks current so the rectangle can surface. The full set of boards is in our sudoku catalog.
Frequently asked questions
What is an X-Wing in sudoku?
An X-Wing is a pattern where a single digit is limited to the same two columns across two different rows, forming a rectangle of four candidate cells. Because those two rows must fill both columns with the digit, it can be eliminated from every other cell in those two columns. The pattern also works with rows and columns swapped.
When should I look for an X-Wing?
After the simpler methods stall. Solve as far as you can with scanning, naked and hidden singles, pairs, and locked candidates first. Only when those run out, and with accurate pencil marks in place, is it worth scanning each digit for the two-by-two rectangle.
Does an X-Wing place a digit directly?
Usually not. An X-Wing removes candidates rather than placing a number, but those removals often expose a hidden or naked single nearby, which does place a digit. It is a tool for unlocking progress, not a direct placement.
How is the X-Wing related to the Swordfish?
They use the same logic at different sizes. An X-Wing links two rows and two columns; a Swordfish links three rows and three columns; a Jellyfish, four of each. All are “fish” patterns built on the idea that a digit confined to a set of parallel units locks the crossing units and clears the digit elsewhere.
