Sudoku

What is this Sudoku tool?

This generates a fresh, valid Sudoku puzzle with a guaranteed unique solution every time, at your choice of three difficulty levels based on how many of the 81 cells are left empty.

The rules

Fill the 9×9 grid so that every row, every column, and each of the nine 3×3 boxes contains the digits 1 through 9 exactly once. The pre-filled numbers (shown in bold) are fixed and can't be changed.

How to use it

1. Pick a difficulty level and click New Puzzle.
2. Click any empty cell and type a number from 1-9.
3. Click Check for Errors at any point to highlight numbers that conflict with Sudoku's rules.
4. Stuck? Click Reveal Solution to see the complete, correct grid.

How the puzzle is generated

The tool first fills a complete, valid 9×9 grid using a randomized backtracking algorithm, then removes cells one at a time — checking after each removal that the puzzle still has exactly one solution, so you'll never hit an unsolvable or ambiguous puzzle. Harder difficulties simply remove more cells, leaving fewer starting clues.