A plain-language walkthrough of the X-Wing elimination — the first "advanced" Sudoku move most players meet, and the one that breaks open stubborn hard boards.
If you can finish easy and medium Sudoku but stall on hard, the gap is almost always one technique: the X-Wing. It is less scary than it sounds, and you do not need notation or memorised patterns to use it.
This guide teaches you to spot it by eye, in about five minutes, using the same board you are already stuck on.
What the X-Wing actually is
An X-Wing happens when a single candidate digit can only appear in two cells of two different rows, and those cells line up in the same two columns. The digit must sit in one of the two columns in both rows — which means it cannot appear anywhere else in those two columns.
In plain terms: you have found a digit "trapped" between four corners. Wherever the real answer is, the other cells in those columns are now safe to eliminate.
How to spot it while playing
Scan one digit at a time. For each row, mark every cell where that digit is still possible. If exactly two rows each have exactly two possible cells, and those four cells form a rectangle, you have an X-Wing.
You do not need to prove it — just eliminate the digit from the rest of the two columns it spans and see what opens up. Most hard boards crack within two such eliminations.
Why it beats guessing
Guessing on a hard board usually costs you the run: one wrong digit cascades. The X-Wing is deduction, so it never backfires. It is also fast — once you can see the rectangle, the elimination takes a second and the rest of the board often solves itself.
FAQ
Do I need to write candidate marks everywhere first?
Only for the one digit you are hunting. Most players scan a digit, sketch its two-rows, and decide — no full pencil-mark grid required.
Is this the same as a Swordfish?
A Swordfish is the three-row version of the same idea. Learn the X-Wing first; the Swordfish follows naturally.