How to Find an X-Wing in Sudoku Without Over-Searching

An X-Wing is easiest when treated as a single-digit question. Choose one candidate and compare its positions across rows or columns.

You are looking for two matching pairs, not a shape to force onto the board.

Choose a scarce digit

Pick a digit that appears in only two or three positions in several rows. A scarce candidate reduces the number of comparisons and makes the rectangle easier to see.

Find matching pairs

If two rows each contain the digit in exactly the same two columns, their four cells form an X-Wing. The same pattern can be rotated: two columns sharing two rows.

Make the rectangle proof

One of the two positions in the first row must hold the digit, and one in the second row must hold it. Therefore the digit can be removed from other cells in those two columns.

Limit the elimination

Remove the candidate only from the matching columns outside the two base rows. Do not change the four corner cells or unrelated rows.

Stop when the scan is empty

If no digit produces a clean pair, return to simpler methods. X-Wings are occasional tools, not a requirement to inspect every candidate on every puzzle.