X-Wing

Difficulty level: expert

An X-Wing forms when two different rows each allow a number in exactly the same two columns. The number must occupy diagonally opposite corners of that rectangle (one per row, one per column) — so every other cell in those two columns can drop the number.

The name comes from the X drawn by the two possible diagonal placements. The same pattern works transposed: two columns each restricting a number to the same two rows eliminates along the rows.

X-Wings are usually the first genuinely 'expert' pattern players learn, and the gateway to its bigger siblings, Swordfish (three rows/columns) and Jellyfish (four).

Worked example

If 9 fits only in the highlighted cells of rows 2 and 7, it must take two opposite corners — so 9 can be erased from the rest of columns 3 and 8.
(highlighted) (highlighted)
(highlighted) (highlighted)

How to apply it

  1. Pick a number and find rows where it has exactly two possible cells.
  2. Look for two such rows whose candidate cells share the same two columns.
  3. Erase the number from all other cells of those two columns.
  4. Re-check the columns for newly forced singles.

Practice it

The fastest way to internalize the x-wing is to use it. Play a free expert puzzle — the in-game hint system points out exactly this pattern when it appears, or browse the full technique library.