Killer Sudoku Online: Rules, Cages, and Where to Start
Learn Killer Sudoku rules, cage sums, best first moves, and where to practice the logic online with Pure Sudoku.
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Get the iPhone App →Killer Sudoku combines classic Sudoku with cage sums. The normal rule still applies: every row, column, and 3×3 box uses the digits 1 through 9 exactly once. The extra rule is that each dotted cage must add up to its small total.
Killer Sudoku Online
Start with the core Sudoku logic
Killer Sudoku depends on clean candidate work. Warm up on Pure Sudoku, then apply the same scanning discipline to cage sums.
How Killer Sudoku Works
A Killer Sudoku grid looks like a normal 9×9 Sudoku board, but groups of cells are surrounded by dotted cage lines. Each cage has a small number. That number is the sum of the digits inside the cage.
For example, a two-cell cage marked 3 can only contain 1 and 2. A two-cell cage marked 17 can only contain 8 and 9. Those simple combinations become powerful when they overlap with rows, columns, and 3×3 boxes.
Best First Moves
How to start a Killer Sudoku puzzle
Find the smallest cages
Two-cell cages with very low or very high totals often have only one possible combination.
Check where the cage sits
A cage that crosses boxes behaves differently from a cage contained inside one box.
Use normal Sudoku rules
Remove any cage combination that repeats a digit in the same row, column, or 3×3 box.
Practice Path
If Killer Sudoku feels noisy, practice regular Hard Sudoku first. The same habits matter: scan before writing notes, avoid guessing, and use candidate eliminations only when the board supports them.
When you are ready, use the new Killer Sudoku landing page as the hub for cage-sum logic and related practice.
Killer Sudoku FAQ
- Can digits repeat inside a Killer Sudoku cage?
- Only when normal Sudoku rules allow it. If two cage cells share a row, column, or 3×3 box, they cannot repeat.
- Is Killer Sudoku harder than regular Sudoku?
- Usually, yes. The cage sums add another layer of logic, but many puzzles become easier once you learn common cage combinations.
- What should beginners practice first?
- Practice Hard Sudoku candidates and small cage combinations before trying very dense Killer Sudoku puzzles.
Practice next
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