Diagonal Sudoku

Printable Diagonal (X) Sudoku Puzzles

Diagonal Sudoku, also known as X Sudoku, plays like a standard 9x9 Sudoku with one extra rule: both main diagonals must contain every digit from 1 to 9 exactly once. That additional constraint forms an X across the grid, which gives the variant its nickname.

This generator produces print-ready Diagonal Sudoku puzzles in A4 or US Letter PDF format, with two puzzles per page and optional solutions. The two diagonals are tinted in the printout so the X constraint stays obvious, which makes the puzzles friendlier for newcomers to variant Sudoku.

Diagonal Sudoku is a rewarding form of brain training that blends classic Sudoku pattern recognition with an extra layer of deductive reasoning. It works well as a quiet-time activity, a travel puzzle, or a classroom enrichment task for children and adults alike.

How the diagonal rule works

Standard Sudoku rules still apply. Place digits 1 to 9 in every row, column and 3x3 box without repetition. The extra rule is simple but powerful.

• The main diagonal from top-left to bottom-right contains every digit from 1 to 9.
• The main diagonal from top-right to bottom-left also contains every digit from 1 to 9.
• These two diagonals share a single cell at the centre of the grid.

In practice the extra constraint often lets you fill the puzzle with fewer starting clues than a standard Sudoku, because the diagonals act almost like extra rows.

Who Diagonal Sudoku is for

Beginners

If you know standard Sudoku, Diagonal Sudoku is a friendly first variant. The tinted diagonals remind you of the rule visually, so you rarely forget to check the X.

Puzzle enthusiasts

Variant Sudoku fans enjoy the extra interaction between rows, columns, boxes and diagonals. It is the kind of puzzle where a single deduction on a diagonal can open up three separate boxes at once.

Classroom teachers

Two puzzles per page gives a short, focused activity. Diagonal Sudoku is also a nice stepping stone when introducing children to the broader family of variant puzzles.

Parents

Print a couple of pages for a long car journey or a calm weekend afternoon. The variant adds interest without making the puzzles intimidating.

What you can customise

• Puzzle count: two per page is the default for clear diagonals.
• Include solutions: add a separate page with fully solved grids.
• Seed: lock the set to reproduce the same puzzles on demand.
• Paper size: choose A4 or US Letter PDF output.

Worked example

Suppose the main diagonal from top-left to bottom-right already contains the digits 2, 5, 7, 9 and 3 in various cells. That leaves four cells along the diagonal still to fill and those cells must contain the digits 1, 4, 6 and 8 in some order. Combine that with the row, column and box restrictions on each of those cells and you often find that only one placement is possible.

Similarly, a single digit placed on the centre cell affects both diagonals, a row, a column and a box all at once, which makes the centre particularly valuable to solve early.

How to use the tool

1. Choose the number of puzzles you want (two per page by default).
2. Decide whether to include the solutions page.
3. Optionally set a seed for a repeatable set.
4. Select A4 or US Letter paper.
5. Click Generate and preview the first page.
6. Download the PDF and print at 100% scale.

Methodology

The generator first builds a fully solved Sudoku grid that also satisfies the extra diagonal constraint. It then removes starting digits, using the diagonals as additional structure to keep the puzzle solvable. Because both diagonals reinforce the row, column and box rules, puzzles can often be set with fewer givens than a comparable classic Sudoku without losing uniqueness.

Tips for solving

• Scan both diagonals first. Any digit that appears on a diagonal tells you a great deal about the centre column and row.
• Use the centre cell’s triple duty. It sits on both diagonals, a row, a column and a box all at once.
• Keep pencil marks light on diagonal cells. Often the diagonal eliminates candidates that would look plausible from the box alone.
• Treat each diagonal as an extra row. When seven digits are placed, the remaining two cells behave exactly like a two-cell row.

Designed for A4 and US Letter printing

The PDF prints cleanly on both A4 and US Letter. Two puzzles per page gives plenty of room to pencil candidate digits in each cell, and the diagonal tint stays visible even on economy printer settings.

Why Diagonal Sudoku is worth trying

Diagonal Sudoku is among the most accessible Sudoku variants. You do not need to learn new arithmetic or a new region shape, just remember to check the X. That low barrier to entry makes it a great introduction for anyone curious about variant Sudoku without wanting a steep learning curve.

At the same time, the diagonals add genuine depth. Because every digit must appear on each diagonal, Diagonal Sudoku often has fewer starting clues than classic Sudoku, which rewards deductive reasoning and pattern recognition over memorised tricks. The tinted diagonals keep the extra rule visible on the printed page, so the puzzle never feels confusing even when cages or arrows are absent.

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