X Sudoku 6×6 Expert — Set 21
Solver Notes
Expert 6x6 X-Sudoku pushes the compact grid to its limits. Few given digits and dense constraint interactions require careful candidate tracking. 10-15 minutes.
X-Sudoku — Free Online & Printable
X-Sudoku adds a diagonal constraint to the classic sudoku rules. Both main diagonals — running from top-left to bottom-right and from top-right to bottom-left — must each contain the numbers 1 through 9 without repetition. This is the most accessible sudoku variant: the two extra constraints actually make many cells easier to deduce, since numbers on the diagonals are additionally restricted. If you''ve mastered standard sudoku and want a fresh twist without learning complex new rules, X-Sudoku (also called Diagonal Sudoku) is the ideal starting point.
About 6x6 Grid
The 6x6 grid strikes a balance between accessibility and depth. With 36 cells in 2x3 boxes, puzzles take 3 to 10 minutes depending on difficulty. The 6x6 is large enough to showcase variant rules meaningfully — Killer cages have room to create genuine arithmetic puzzles, Windoku windows overlap in interesting ways — while remaining completable in a single sitting. Many players find the 6x6 their "daily driver" format: challenging enough to be satisfying, short enough to fit into a break.
Expert Difficulty
Expert difficulty requires advanced solving techniques that go beyond basic elimination. Expect to use X-wing patterns (where a candidate appears in exactly two cells across two rows that align in the same two columns), swordfish (three-row X-wing extension), and XY-wing (three-cell chain eliminations). For Killer Expert, complex cage arithmetic with 3-4 possible combinations that must be narrowed through cross-cage deduction. Most expert solvers use full candidate notation. Average time: 40-60 minutes for 9x9. Not recommended as a first attempt at any variant.
How to Get Started
- Choose "New Puzzle" to generate a fresh puzzle with a unique solution
- Click or tap cells to enter numbers (1-6 for 6x6)
- Use the constraint highlights to track which numbers are still available
- Print the puzzle if you prefer solving on paper