Is every generated puzzle guaranteed to have a unique solution?

No. This is a simplified generator, not a full backtracking constraint solver. It always produces a valid, fully-solved grid before blanking cells, but it does not verify that the resulting puzzle (after blanking) has only one possible solution.

How many cells can be blanked?

Between 0 and 64 of the 81 cells. 0 blanks returns the complete solved grid; higher blank counts produce a sparser, harder-looking puzzle.

How is the base grid built?

It starts from the classic row-shift formula (row*3 + row/3 + col) mod 9, which always yields a valid Sudoku Latin square, then shuffles bands, rows within each band, stacks, columns within each stack, and the 1-9 digit labels to vary the layout.

What does '.' mean in the output?

A period marks a blanked cell, the ones you're meant to fill in when solving the printed puzzle.

Sudoku Board Generator - Create a Sudoku Puzzle Online

Overview

Introduction

This tool generates a random, valid 9x9 Sudoku grid and turns it into a puzzle by blanking out a chosen number of cells.

It's a decorative/practice generator: every full grid it builds is a genuinely valid Sudoku solution, but the blanking step is simple random removal rather than a solver-verified puzzle design.

What Is Sudoku Board Generator?

A generator that produces a complete, rule-following 9x9 Sudoku grid (every row, column, and 3x3 box contains 1-9 exactly once), then replaces a requested number of cells with '.' to present as a solvable puzzle.

The underlying grid comes from a well-known deterministic construction, varied with random symmetry-preserving shuffles so repeated generations look different.

How Sudoku Board Generator Works

A base grid is built with the formula (row*3 + floor(row/3) + col) mod 9 + 1, which always produces a valid Sudoku Latin square.

Random shuffles of the three bands, the rows within each band, the three stacks, the columns within each stack, and the 1-9 digit labels are applied; each of these operations preserves Sudoku validity.

Finally, a random selection of cells (up to your requested blanks count) is replaced with '.' to form the puzzle.

When To Use Sudoku Board Generator

Use it to quickly generate a Sudoku grid for printing, practice, or embedding in a text-based document.

It's also handy for testing Sudoku-solving code with grids that are always guaranteed to have started from a valid solution.

Often used alongside Magic Integer Generator and Integer Matrix Generator.

Features

Advantages

Every full (0-blank) grid it produces is a genuinely valid, rule-following Sudoku solution.
Fast, purely client-side generation with no external puzzle database.
Plain monospace text output that copies and pastes cleanly anywhere.

Limitations

Does not guarantee a unique solution for the blanked puzzle: it's a simplified generator, not a full backtracking constraint solver, so some blank counts could in principle admit more than one valid fill.
Blanking is purely random, so difficulty is not tuned or rated.
Capped at 64 blanks (out of 81 cells) to always leave at least some starting clues.

Examples

A fully solved grid (0 blanks)

Input

Output

5 3 4 6 7 8 9 1 2
6 7 2 1 9 5 3 4 8
1 9 8 3 4 2 5 6 7

8 5 9 7 6 1 4 2 3
4 2 6 8 5 3 7 9 1
7 1 3 9 2 4 8 5 6

9 6 1 5 3 7 2 8 4
2 8 7 4 1 9 6 3 5
3 4 5 2 8 6 1 7 9

With 0 blanks, the full valid grid is shown (exact digits vary run to run since bands/rows/digits are randomly permuted).

A puzzle with blanks

Input

Output

. 3 . 6 7 . 9 1 .
6 . 2 . 9 5 . . 8
. 9 8 3 . . 5 6 7

. 5 9 . 6 1 4 . 3
4 2 . 8 . 3 7 9 .
7 . 3 9 2 . 8 5 6

9 6 . 5 . 7 2 . 4
2 8 7 . 1 9 . 3 5
. 4 . 2 8 . 1 7 9

With 40 blanks, roughly half the cells are replaced with '.', leaving a printable puzzle grid.

Best Practices & Notes

Best Practices

Use a monospace font/context so the space-separated columns stay visually aligned.
Click Regenerate a few times if you want a fresh layout without changing the blanks count.

Developer Notes

The base grid uses the standard row-shift Latin square formula, then applies Fisher-Yates shuffles to bands, in-band rows, stacks, in-stack columns, and the digit labels (all Sudoku-validity-preserving symmetries) before uniformly sampling which cells to blank.

Sudoku Board Generator Use Cases

Printing a quick Sudoku puzzle for practice
Seeding test fixtures for Sudoku-solving or Sudoku-validating code
Generating placeholder puzzle content for a demo or mockup

Common Mistakes

Assuming a generated puzzle has exactly one solution; it isn't solver-verified.
Viewing the output in a proportional font, where columns won't align.
Requesting more than 64 blanks, which is rejected to keep at least some starting clues.

Tips

Set blanks to 0 to get a complete, valid solved grid instead of a puzzle.
Lower blank counts (around 30) tend to look like 'easy' puzzles; higher counts (55+) look sparser and harder.

Sudoku Board Generator