X-Wing practice sheets

The sheet people actually search for

X-Wing is the technique where sudoku stops being arithmetic and becomes pattern reading. It is also the one most players learn from a diagram, nod at, and then never manage to find on a real board — because a diagram shows you four neat cells and a real board shows you eighty-one cells and a mess of pencil marks.

This page exists for that gap. Every puzzle here is generated, then replayed with the cheapest technique first, the way a person solves; the puzzle is kept only if an X-Wing is used somewhere on that path. The filter runs in your browser on each visit, so the set is fresh each time — which is what you want for drilling a scan.

Spotting one, in order

1. Take one digit at a time. X-Wing is always about a single digit. Pick one that is already placed several times; it has fewer cells left.
2. Count its homes in each row. You are looking for rows where the digit has exactly two possible cells. One such row is not enough — you need a matching pair of rows.
3. Check whether the four cells form a rectangle. Two rows, each with two homes, and the two homes in the first row sit in the same two columns as the two homes in the second row. That is the pattern.
4. Eliminate along the other direction. If the base was the two rows, the digit is impossible in the rest of those two columns. If the base was the two columns, the digit is impossible in the rest of those two rows.

The trap is step 3: a digit with two homes in two rows is common, and it usually fails the rectangle test. Do not stop counting until both rows agree on the same two columns.

What the grader guarantees

Every puzzle on the sheet needs at least one X-Wing, and nothing on it asks for more than one tier above: the hardest extra step you can meet is a skyscraper, an XY-Wing or a unique rectangle. Expect a few sheets where a puzzle needs one of those to finish — that is the honest state of the difficulty ladder, not a bug. The filter never relaxes to fill a sheet, so if one comes up short, press New set.

Printing it

Scale 100% (not "fit to page" — that thins the box lines). One or two puzzles per page leaves room to write; four per page is a set you can work through in a sitting.

Candidate marks matter more on this sheet than on any other. An X-Wing lives entirely in the candidate grid: with printed marks you are comparing lists, without them you are holding four lists in your head and guessing. If you print one copy to learn on, print it with marks on; print a second without, later, to check whether you can now find the pattern unaided.

Answer page puts the solutions on separate sheets at the end, numbered to match the puzzles.

Where to go next

The full guide to X-Wing has a worked position pulled from a real game, the case-by-case proof of why the elimination is safe, and an honest section on what an X-Wing does not prove — it never places a digit, it only removes candidates.

Once the rectangle is easy to see, the skyscraper sheet is the natural next step: same scan, one corner missing. If you want the harder version first, try swordfish — three lines instead of two, nine cells instead of four.