Expert Irregular Diagonal Sudoku

Jigsaw regions plus two diagonal constraints — every digit 1–9 must appear once in each row, column, region, and diagonal. Free to play.

Easy Medium Hard Expert

Expert Irregular Diagonal Sudoku. The hardest combined-variant puzzles on the site — every step chains diagonal, region, row, and column logic simultaneously.

4
7
2
1
7
9
6
3
2
1
7
8
4
1
5
2
3
5
8
8
5
4
7
9
3
Mistakes
0/3
Score
-
Time
00:00
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Progress0%

What is Irregular Diagonal Sudoku?

Difficulty
★★★★☆
4/5
Constraint Type
Combined: Irregular + Diagonal
Typical Givens
22–30
Avg. Solve (Expert)
65 min

Solving Techniques for Expert Level

Technique Description Level
Map All 29 Units First You have 9 rows + 9 columns + 9 irregular regions + 2 diagonals = 29 constraint units. Identify all irregular regions and both diagonals before starting. Beginner
Diagonal–Region Intersection Cells on a diagonal that also sit in the same irregular region create a powerful two-unit intersection — use both constraints simultaneously. Intermediate
Diagonal Pointing Pairs If a digit on a diagonal is confined to one irregular region, eliminate it from all other cells of that region. Intermediate
Region Coloring for Diagonals Trace which irregular regions each diagonal passes through. Regions with many diagonal cells are the most constrained. Advanced
Chain Deduction Across Units With 29 units, a forced digit in one unit often cascades through 3–4 other units. Track chains carefully to avoid errors. Advanced

Average Solve Time by Difficulty

Easy
8 min
Medium
18 min
Hard
35 min
Expert
65 min
Want a full walkthrough of rules, strategies, and solving steps? How to Play Irregular Diagonal Sudoku →

Frequently Asked Questions — Expert Irregular Diagonal Sudoku

Is expert Irregular Diagonal Sudoku the hardest Sudoku variant on the site?
It is one of the hardest. Expert puzzles combine jigsaw regions, diagonal uniqueness, and very few givens. Every step requires reasoning about at least two constraint types simultaneously, and no placement follows from a single-constraint observation alone. It demands full concentration and advanced technique.
Can expert Irregular Diagonal Sudoku be solved without guessing?
Yes — all puzzles on Sudoku.by have a unique logical solution. Expert puzzles require advanced techniques such as X-Wings applied across diagonals, multi-region forcing chains, and diagonal-region intersection logic, but every deduction follows from provable reasoning. No guessing is needed or helpful.
What is a diagonal X-Wing in this variant?
A diagonal X-Wing occurs when a digit appears as a candidate in exactly two cells on each of the two main diagonals, and the four cells form a rectangle. If the digit can only go in two columns (or rows) across those four cells, it can be eliminated from all other cells in those columns or rows. This is a rare but powerful pattern specific to diagonal variants.
How do I approach an expert puzzle when I feel completely stuck?
Step back and audit your candidate lists — make sure every elimination from recent placements is reflected. Then look at each digit separately: for each digit, how many cells across the entire board still have it as a candidate? A digit with very few remaining candidates (four to six) is usually the one whose placement unlocks the next chain.
How long does an expert Irregular Diagonal Sudoku take to solve?
Most players need 75–120 minutes for expert puzzles. Highly experienced variant solvers may finish in 50–80 minutes. If you've spent 30 minutes without a single new placement, return to the two diagonals and look for a pointing pair you may have overlooked — it is almost always there.

More questions? See the full Irregular Diagonal Sudoku guide.