The Swordfish is a natural extension of the X-Wing pattern, scaled up from a 2x2 grid alignment to a 3x3 configuration. It occurs when a candidate digit appears in two or three cells within each of three different rows, and all those candidate positions are confined to the same three columns. Because the digit must appear exactly once in each row, the three rows collectively account for three placements of that digit, and those placements must all fall within the three identified columns. This means the candidate can be eliminated from all other cells in those three columns.
Unlike the X-Wing, where every corner of the rectangle must contain the candidate, a Swordfish does not require every intersection cell to hold the candidate. As long as each of the three rows has the candidate in only two or three positions within the three columns, the logic holds. This makes Swordfish patterns harder to spot because the grid of nine potential cells may be only partially filled with the candidate, creating irregular shapes rather than a clean rectangle.
The Swordfish is the second member of the fish technique family and a crucial tool for tackling puzzles rated hard or extreme. Learning to identify Swordfish patterns strengthens your ability to analyze candidate distributions systematically across multiple rows and columns simultaneously. Once you can reliably find Swordfish, you are well-prepared for its larger sibling, the Jellyfish, and other complex set-based elimination strategies.
Try It Yourself
Walk through each step of the swordfish technique on a real puzzle. Follow the instructions and try entering the correct value when prompted.
We are tracking candidate 1 across the grid. Examine rows 1, 4, and 5 for the positions where 1 can appear. Note which columns hold candidate 1 in each row.
Step-by-Step Guide
Select a candidate digit and map its positions across all nine rows.
Identify rows where the candidate appears in only two or three cells.
Try to find three such rows where all candidate positions fall within the same three columns.
Verify that each of the three rows has the candidate only within those three columns.
Confirm the pattern cannot be reduced to a simpler X-Wing.
Eliminate the candidate from all other cells in the three columns outside the Swordfish rows.
Check the grid for new singles or further deductions enabled by the eliminations.
Think of three bus routes that only stop at three specific stations — since every route must use one station, no other route can claim those stations.
The three rows each impose an independent constraint requiring exactly one placement of the digit, and since all candidate positions are confined to the same three columns, those three rows must collectively place the digit exactly three times within those three columns. By the pigeonhole principle, three placements across three columns means one placement per column, fully satisfying each column's constraint and leaving no room for additional placements of that digit anywhere else in those columns.
When to use: Use Swordfish when X-Wing fails but you notice a candidate confined to two or three positions in each of three rows (or columns), all within the same three columns (or rows).
Common Mistakes to Avoid
Requiring all nine intersection cells to contain the candidate.
Unlike X-Wing, Swordfish only needs each of the three rows to have the candidate in two or three cells within the three columns. Not all nine intersections need the candidate.
Confusing a Swordfish with three separate X-Wings.
A Swordfish is a single pattern across three rows and three columns. If you can reduce it to independent X-Wings, it is not a true Swordfish.
Eliminating from the Swordfish rows instead of the Swordfish columns.
When the pattern is row-based, eliminations occur in the columns (outside the three Swordfish rows), and vice versa.
More Examples
See swordfish applied in different puzzle configurations to strengthen your pattern recognition.
Swordfish on Digit 1
Highlighted cells show the swordfish pattern
Practice Puzzles
Apply the swordfish technique on these mini challenges. Tap a highlighted cell and enter the correct digit.
Quick Reference
- Pattern:
- A candidate in exactly 2-3 cells per row across three rows, confined to three columns
- Action:
- Eliminate that candidate from all other cells in those three columns
- Look for:
- A candidate forming a 3x3 fish pattern across rows and columns