Play Killer X Sudoku Online Free

Play Killer X Sudoku online for free. The cage-sum challenge of Killer Sudoku combined with the X-Sudoku rule that both main diagonals also contain digits 1–9.

▶ Play Killer X Sudoku — Free
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How to Play Killer X Sudoku

  1. Standard Sudoku rules: every row, column, and 3×3 box contains 1-9.
  2. Dotted cages show a target sum — digits inside must add up to it. No digit can repeat within a cage.
  3. Both main diagonals must also contain digits 1–9, each exactly once.
  4. Diagonal cells live under five constraints at once: row, column, box, cage, and diagonal.
💡 Pro Tip
Diagonal cells are the most constrained on the board — start there. A diagonal cell sitting in a tightly-summed cage often has just one possible digit.

Frequently Asked Questions

How does Killer X Sudoku differ from regular Killer Sudoku?

Killer X adds the X-Sudoku diagonal constraint: digits 1–9 must each appear exactly once on each of the two main diagonals, in addition to all the cage and standard sudoku rules.

Is Killer X harder than Killer Sudoku?

Not always harder — the diagonal constraints often help you find forced digits faster. But the puzzle space is smaller, so solo Killer X puzzles can reach lower clue counts than pure Killer.

Try More Puzzle Modes

🧩Killer Sudoku 🧩X-Sudoku (Diagonal Sudoku) 🧩Classic Sudoku 🧩Arrow Sudoku
▶ Play Killer X Sudoku