Swordfish Practice Puzzles

Every puzzle below is verified to feature the Swordfish as its hardest required technique — of the 65,284 puzzles in our library, 12,015 require it and 12,015 need nothing harder. New to the pattern? Learn the Swordfish or see a worked example first.

How to drill the Swordfish

A Swordfish is the X-Wing argument extended to three lines and three columns, and the single most important thing these puzzles teach is that the rows do not each need exactly three candidate cells. Two is fine. What matters is that across three rows, the digit's possible positions fall entirely within the same three columns.

Solvers who learn the pattern as a tidy three-by-three grid of candidates find only the textbook cases and conclude Swordfish are rarer than they are. Learning it as a containment condition — three rows, three columns, nothing outside — finds the rest.

It is also worth being honest about when this is the right tool. A Swordfish is expensive to search for, and on most stalled grids there is a cheaper elimination still available. These puzzles are constructed so that there genuinely is not, which is what makes them useful practice rather than a test of patience.

Curated Swordfish puzzles

  1. Practice puzzle #1 — 24 givens · needs Naked Single, Swordfish
  2. Practice puzzle #2 — 23 givens · needs Naked Single, Swordfish
  3. Practice puzzle #3 — 26 givens · needs Naked Single, Hidden Single, Swordfish
  4. Practice puzzle #4 — 26 givens · needs Naked Single, Hidden Single, Swordfish
  5. Practice puzzle #5 — 24 givens · needs Naked Single, Hidden Single, Swordfish
  6. Practice puzzle #6 — 24 givens · needs Naked Single, Hidden Single, Swordfish
  7. Practice puzzle #7 — 25 givens · needs Naked Single, Hidden Single, Swordfish
  8. Practice puzzle #8 — 24 givens · needs Naked Single, Hidden Single, Swordfish
  9. Practice puzzle #9 — 25 givens · needs Naked Single, Hidden Single, Swordfish
  10. Practice puzzle #10 — 25 givens · needs Naked Single, Hidden Single, Swordfish
  11. Practice puzzle #11 — 23 givens · needs Naked Single, Hidden Single, Swordfish
  12. Practice puzzle #12 — 25 givens · needs Naked Single, Hidden Single, Swordfish
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Swordfish practice FAQ

How many Sudoku puzzles require the Swordfish technique?
Of the 65,284 puzzles in the Precision Sudoku library, 12,015 require the Swordfish to solve, and 12,015 can be completed with nothing harder than the Swordfish. Every puzzle is verified by a solver that records the exact techniques needed.
Does each row in a Swordfish need exactly three candidate cells?
No, and believing so is the main reason Swordfish get missed. A row may contribute two candidate cells instead of three. The requirement is only that across the three rows, every possible position for the digit lies within the same three columns.
How is a Swordfish different from an X-Wing?
It is the same argument one size larger. An X-Wing confines a digit to two lines and two crossing lines; a Swordfish confines it to three and three. Both conclude that the digit can be removed from the crossing lines everywhere outside the pattern.