An example Argyle puzzle: no digit repeats along each marked diagonal - here 2, 5, 8 and 3, 6, 9.
Argyle Sudoku draws a set of diagonal lines across the grid in the criss-cross pattern of an argyle sock or sweater. Along each marked diagonal, no digit may repeat - exactly like the diagonals of X-Sudoku, but there are several of them, running both ways, and most are shorter than the full corner-to-corner line.
The rule: no repeats along a marked diagonal
Wherever the argyle pattern draws a diagonal, treat it like an extra unit: every cell on it must hold a different digit. Below, one marked diagonal carries 3, 7, 1, 9, 5 - all different.
A marked diagonal (dashed): its digits 3, 7, 1, 9, 5 are all different.
A worked example, step by step
Take a marked diagonal that already shows a 3 and a 7.
Step 0. The diagonal shows 3 and 7; three cells remain.
Step 1 - the diagonal bans its own digits. Because no value repeats on the diagonal, the remaining three cells can be neither 3 nor 7 - on top of whatever their rows, columns and boxes already forbid.
Step 1. 3 and 7 are barred from the rest of the diagonal.
Step 2 - stack the constraints. Each remaining diagonal cell also sits on its own row, column and box, so the diagonal ban combines with those to leave very few candidates - often a single one. Where two marked diagonals cross, a cell feels both diagonal bans at once, which is where Argyle puzzles crack open.
Why several short diagonals help
A single long diagonal (as in X-Sudoku) is a strong clue; a lattice of shorter ones spreads that strength across the whole grid. Even a three- or four-cell diagonal bans its digits from each other, and because the argyle lines overlap, many cells lie on two diagonals at once. Tracking which diagonals a cell belongs to is the key skill.
Solving strategy
- Treat each diagonal as a unit. Scan it for repeats exactly as you would a row or box.
- Target the crossings. A cell on two marked diagonals carries two extra bans - start there.
- Combine with the grid. The diagonal ban plus the ordinary rules usually leaves a cell one candidate.
- Feed the grid. Each diagonal digit placed behaves like a given for its row, column and box.
Common mistakes
- Missing a diagonal. Argyle marks several lines both ways - check every one a cell lies on.
- Treating unmarked diagonals as constrained. Only the drawn diagonals carry the no-repeat rule.
- Overlooking the crossings. The cells on two diagonals are the most constrained - don't skip them.
- Forgetting ordinary Sudoku. Diagonal cells still obey their rows, columns and boxes.
Can I play it here?
Not yet - Argyle Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile:
- Try the closely related X Sudoku, which you can play right now.
- Browse all the Sudoku variants we do offer.
- Or print free puzzles from the printable PDF page.
Where to play it
Argyle Sudoku belongs to the constraint family and runs on 9×9. It is not one SudokuStreak generates yet - but the deduction it trains is the deduction every Sudoku runs on.
Difficulty and type are two separate dials here: the type sets the extra rule, the level sets how much of the grid you start with. Hard Sudoku leaves 26 of the 81 cells filled, where scanning gets you started and then leaves you stranded; Expert Sudoku leaves 25, where the beginner tools dry up almost entirely. Take it at the gentler end while the pattern is still new, and move up once it stops being a fight.