What is X-Sudoku?
X-Sudoku is normal sudoku with one extra rule. The grid is the same 9×9 you know, with the same 3×3 boxes. But the two big diagonals — the one going from the top-left corner to the bottom-right corner, and the one going from the top-right corner to the bottom-left corner — also have to use the numbers 1 to 9 without any repeats.
Those two diagonals make a giant X across the board. That’s where the name "X-Sudoku" comes from. Some puzzle books also call it "Sudoku X" or "Diagonal Sudoku", but the rules are exactly the same. If you’re already comfortable with our classic 9×9 sudoku, you already know most of the rules. X-Sudoku just adds the two diagonals on top.
We’ve tinted the two diagonals a gentle lavender colour so you can see them clearly. They stay the same colour whether you’re clicking around the board or not — that’s on purpose, so the X never disappears while you’re solving.
How is X-Sudoku different from regular sudoku?
In a normal sudoku you have three rules: every row, every column and every 3×3 box must contain the digits 1–9 with no repeats. X-Sudoku keeps all three of those rules and adds a fourth one — the two big diagonals must ALSO contain 1–9 with no repeats.
The nine cells on each diagonal are treated just like a normal row or column: you can never put the same number twice on the same diagonal. If you’re about to place a 7 on the top-left-to-bottom-right diagonal and there’s already a 7 somewhere on that diagonal, that move is blocked — even if the row, column and box all look fine.
- 🟪 Every row, column and 3×3 box must contain 1–9 (same as classic sudoku)
- ✖️ Both big diagonals must also contain 1–9 with no repeats
- 🎨 The two diagonals are tinted so you can see them without counting cells
- 🎯 The extra rule gives you extra clues — solving can actually feel FASTER
The 4 simple rules
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One of each in every row
Every row needs the digits 1 through 9 — no repeats.
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One of each in every column
Every column needs the digits 1 through 9 — no repeats.
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One of each in every box
Each 3×3 box needs the digits 1 through 9 — no repeats.
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One of each on each diagonal
The two big diagonals (top-left-to-bottom-right and top-right-to-bottom-left) must each contain the digits 1 through 9 — no repeats.
The diagonal trick that unlocks X-Sudoku
The biggest shift going from classic sudoku to X-Sudoku is learning to "see" the two diagonals as real lines, not just decoration. Any time you’re about to place a digit on one of them, you have to check four things instead of three: the row, the column, the 3×3 box, AND the diagonal.
That sounds like more work, but in practice it’s a huge gift. The centre cell of the grid sits on BOTH diagonals at once, so solving it uses five different lines to pin down a single digit. Cells near the middle are the easiest to solve on any X-Sudoku.
A great way to start every puzzle is to look at the two diagonals first. Count the digits already on each one — if a diagonal has seven of the nine digits, the other two are almost solved already.
Easy strategies for kids
- ✨ Solve the centre cell first when you can — it sits on both diagonals
- 📐 Scan both diagonals before every move
- 🔢 Use the 45-sum trick on a nearly-full diagonal
- ✏️ Tap Notes to pencil in possible candidates
- 💡 Auto Notes takes the diagonals into account for you
Most kids pick up X-Sudoku in about five puzzles. If you’ve never played sudoku of any kind, a couple of rounds at Easy 9×9 sudoku first will get the basic pattern into your head. Once rows, columns and boxes feel automatic, the X is a fun extra layer on top.
Why kids love X-Sudoku
- 🧠 Trains visual thinking — spotting patterns on diagonal lines
- 🎨 The tinted X makes every puzzle look lovely and clear
- 🕵️ Detective brain — the extra rule gives you extra clues
- ⏱️ Quick wins on Easy, longer challenges on Expert
- 📱 Plays great on phones, tablets, Chromebooks and laptops
Ready for more?
Once Easy X-Sudoku feels comfortable, try Medium X-Sudoku. From there you can graduate to Hard X-Sudoku, and finally take on Expert X-Sudoku — our toughest diagonal puzzle.
Want a totally different brain workout? Try our Killer Sudoku (sudoku with cage sums) or our Jigsaw Sudoku (classic rules, but the boxes are wiggly shapes). Younger players can also try our 4×4 sudoku and 6×6 sudoku starter grids.
Frequently asked questions
What age is X-Sudoku good for?
Most kids enjoy X-Sudoku from about 8 years old, once they’re comfortable with regular sudoku. Younger kids should start with our 4×4 or 6×6 starter grids, then move to classic 9×9, and add the X rule when rows, columns and boxes feel automatic.
Is X-Sudoku harder than normal sudoku?
Not always! The extra diagonal rule adds more constraints, but it also gives you more clues. On Easy and Medium, most kids find X-Sudoku about the same difficulty as regular sudoku — sometimes even a bit quicker.
Why is it called X-Sudoku?
The two big diagonals going corner-to-corner cross in the middle of the board and draw a giant X shape. The X is the extra rule, so the puzzle is named after it.
Is X-Sudoku the same as Sudoku X or Diagonal Sudoku?
Yes — X-Sudoku, Sudoku X, Diagonal Sudoku and Crossover Sudoku are all the same puzzle. Different sites and puzzle books use different names, but the rules never change.
Can I play without making an account?
Yes! Every game on this site is free, with no signup, no email, and no ads in the way of the puzzle.
Does it save my progress?
Yes — your puzzle, notes and timer save automatically in your browser. Close the tab and come back later, it’ll still be there.
Try other sudoku games
Different rules, same friendly board. Pick a sibling puzzle to play next.