---
title: "Swordfish: Sudoku Technique #15 | Sudoku Flow"
description: "Swordfish: When a number's candidates in three rows all fall within the same three columns (or in three columns all fall within the same three rows), that…"
url: https://sudokuflow.com/lessons/swordfish/
language: en
---

[Sudoku technique lessons](https://sudokuflow.com/lessons/) / Swordfish

Lesson 15

# Swordfish

## The rule

When a number's candidates in three rows all fall within the same three columns (or in three columns all fall within the same three rows), that candidate is removed everywhere else in those three crossing lines.

## Step by step

1. In each base row, 5 is a candidate in 2 or 3 cells. Taking the three base rows together, every 5 candidate sits in one of only three columns. This is a Swordfish!
2. The Swordfish means we can remove the candidate 5 from the three columns that hold it, in every cell outside the three base rows.

[Read the full lesson, with more examples →](https://sudoku.rubigogames.com/techniques/swordfish.html)

In our app, when this technique is the next step, the hint names it and shows you why, step by step. No ads, free to download.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_cta&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dcta%26utm_campaign%3Dlesson)

## Try it on more boards

Each board is a real puzzle from our app, at a moment where Swordfish applies. Find the step yourself, or tap Hint and the app's own hint walks you through it.

Swordfish practice board:

```text
5  .  9  | 2* 4* 6* | .  7  1*
.  4  .  | 7  1* 5* | .  9  6*
6* 7* 1  | 3* 8* 9  | 5  2  4
---------+----------+---------
.  5  .  | 9  7* .  | .  .  3
9  .  .  | 5  3* 2  | 7  .  8
3  .  7* | 8  6  .  | 9* .  .
---------+----------+---------
.  9* .  | .  2  .  | .  .  .
7  .  .  | 1  5* .  | 6  .  9
.  .  .  | .  9* .  | .  8  .
```
Digits marked * were filled in by a player; the others were printed with the puzzle.

![Sudoku app icon](https://sudokuflow.com/assets/app-icon.png)

## Want more boards like this?

We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_web&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dweb%26utm_campaign%3Dsite)

Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.