X Sudoku 4×4 Easy — Set 81
Solver Notes
The smallest X-Sudoku grid at the gentlest difficulty. A 4x4 Easy puzzle takes under a minute and is the perfect introduction to diagonal constraints.
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 4x4 Grid
The 4x4 grid is the introductory format for variant sudoku. With only 16 cells organized into 2x2 boxes, a 4x4 puzzle takes 30 seconds to 2 minutes to solve. At this size, the variant rules (diagonal constraints, window regions) are immediately visible and easy to apply — perfect for understanding how a new rule changes the solving experience before tackling larger grids. The 4x4 is specifically recommended as a first puzzle when learning X-Sudoku, giving you a low-stakes environment to understand diagonal constraints without the cognitive load of a full 9x9.
Easy Difficulty
Easy difficulty assumes you already know standard sudoku and are learning a new variant. Puzzles are designed so that the variant's unique rule creates clear, immediate deductions: in X-Sudoku Easy, most diagonal cells can be filled using only the diagonal constraint plus row/column logic. Solving technique required: naked singles (cells with only one possible value) and direct constraint elimination. No candidate markup needed. Average time: 3-8 minutes for 9x9, 30-90 seconds for 4x4.
How to Get Started
- Choose "New Puzzle" to generate a fresh puzzle with a unique solution
- Click or tap cells to enter numbers (1-4 for 4x4)
- Use the constraint highlights to track which numbers are still available
- Print the puzzle if you prefer solving on paper