Diagonal Sudoku

How to play diagonal sudoku

Diagonal sudoku, also called sudoku X, adds the two long diagonals as extra houses. Each diagonal must hold 1 to 9 once, just like a row, a column or a box.

The center cell is on both diagonals, and every diagonal cell sees more of the grid than usual. Our puzzles are set so the diagonals are needed to finish.

Diagonal sudoku: full lesson

See the rule in 15 seconds

At a glance

• Both long diagonals hold 1 to 9 once.
• The center cell sits on both diagonals.
• Each diagonal crosses three boxes.
• Also called sudoku X or X-sudoku.

How the diagonals work

The two shaded lines are extra houses. Each one crosses three boxes and shares the center cell, so a digit on one diagonal rules out more of the grid than usual.

How to start a diagonal sudoku

1. Scan the diagonals like a row

   Each diagonal is a ninth house. Check which digits it's missing and where they can go, just like a row.

2. Watch the center cell

   r5c5 is on both diagonals, its row, its column and the middle box: five houses. It's often one of the first cells to fall.

3. Use the corners of each box

   In boxes 1, 3, 7 and 9, three cells lie on a diagonal. In box 5, five do. A digit placed on a diagonal clears those cells in other boxes.

4. Pointing pairs along the diagonal

   If a box's candidates for a digit all lie on a diagonal, that digit comes off the rest of the diagonal. It's a pointing pair with a new kind of line.

5. Fall back on classic technique

   Diagonal sudoku is classic sudoku with two more houses, so every classic technique still applies.

Common mistakes

Five levels, no guessing

Every puzzle has one solution, proved when it is set, and our solver finishes it by logic alone. The level is the hardest step the solve needs. Here is what each level asks of a diagonal puzzle:

1. EasySingles, with the diagonals as two more houses.Play Easy
2. MediumPointing pairs and box/line reductions, including along the diagonals.Play Medium
3. HardNaked and hidden pairs and triples.Play Hard
4. ExpertX-Wings, Skyscrapers and wings.Play Expert
5. FiendishColoring and chains. Never a guess.Play Fiendish

The daily variant rotates through 11 kinds, so a diagonal daily comes round about every 11 days. Past dailies

Hand-set diagonal puzzles

Our levels are a good start. For more, Explore has 61 diagonal puzzles made by people, from Logic Masters and Cracking the Cryptic. A few of the most popular:

Modular Miracleby masetabSchubladenby Myxo2026 Killerby Florian WortmannQuality Streetby Jay DyerFollow-on Arrowsby Aad van de WeteringDiagonalityby The Book WyrmSan Joséby ICHTUESMajor Diagonals Speed Runby Will Power

Setters with the most diagonal puzzles:

• gwai77 4
• Florian Wortmann 3
• Merdock 3
• pagedo 2
• Aad van de Wetering 2
• ICHTUES 2
• Will Power 1
• PhoenixAki 1
• Gerhard1963 1
• Blobz 1

Often combined with:

• Diagonal + Kropki 24
• Diagonal + Killer 18
• Diagonal + German Whispers 16
• Diagonal + Renban 14
• Diagonal + Arrow 11
• Diagonal + XV 10
• Diagonal + Thermo 8
• Diagonal + Odd/Even 8
• Diagonal + Fog of War 7
• Diagonal + Region Sum Lines 5

All 61 diagonal puzzles in Explore · Make your own diagonal sudoku

Questions

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