Peak Sudoku
Fish, wings, chains & uniquenessPeak Score 60–75

Swordfish

The 3-row / 3-column generalisation of an X-Wing.

Also known as: 3-Fish, Three-Line Fish

Quick Summary

A Swordfish occurs when a candidate digit in three rows is confined to at most three columns. The digit can be eliminated from all other cells in those three columns.

Understanding the Swordfish Technique

The Swordfish extends the X-Wing logic into three dimensions of lines. In three separate rows, a candidate appears in cells that collectively belong to only three columns. Because each of the three rows must contain the digit, and no two can share a column, the digit must occupy one cell in each of the three columns. Consequently, no other cells in those three columns can hold that candidate.

Visual Examples

Green cells highlight the Swordfish pattern, amber cells denote where candidates are affected, and struck-through pencil marks show the eliminations. Use the buttons or arrow keys to browse examples.

Example 1 of 5
Across rows 2, 3, 6, the digit 5 sits only in columns 3, 4, 8. Those rows fill those columns with their 5s, so 5 can be removed from the rest of columns 3, 4, 8.
Removes: 5 from R1C3, R1C4, R5C4, R1C8

How to Spot & Solve a Swordfish (Step-by-Step Guide)

The complete visual scanning and logical deduction process to execute this technique:

  • 1Select a digit and find three separate rows where it only appears in two or three cells.
  • 2Verify that across all three rows, the candidate cells only fall into three shared columns.
  • 3Because each of the three rows must contain the digit, and no two can share a column, the digit must occupy one cell in each of the three columns.
  • 4The digit is completely locked into those three columns across the three rows.
  • 5Eliminate that candidate from every other cell along those three columns.

Common Traps & Mistakes to Avoid

  • Having candidate cells in a fourth column in one of the three rows.
  • Thinking each row must contain all three columns; having only 2 candidate cells per row is common and fully valid.
  • Failing to check for column-based Swordfish (where 3 columns project onto 3 rows).

Frequently Asked Questions

How many cells make up a Swordfish?

A Swordfish can consist of anywhere from 6 to 9 cells (minimum 2 per row across 3 rows).

Is Swordfish common in daily puzzles?

Swordfish appears regularly in Tough and Expert puzzles. Recognizing it is essential for solving without guessing.

Expand your repertoire by learning prerequisites and advanced counterparts:

X-WingPeak Score 55–70

A digit restricted to exactly two cells in two different rows, forming a rectangle.

Read guide →
JellyfishPeak Score 70–85

The 4-row / 4-column version of Swordfish.

Read guide →

Ready to Practice Swordfish?

Try a puzzle in the Tough tier (Peak Score 61–70), or browse all 25 techniques.

Play Tough puzzleAll 25 techniques