BYTETOOLS

Sudoku Generator

Generate printable sudoku puzzles with a guaranteed unique solution. Choose easy to expert, rebuild any puzzle from its seed and download the answer key.

34
Clues given
47
Empty cells
Exactly 1
Solutions

Sudoku puzzle — medium

Sudoku puzzle grid
346
31
26859
26
62458
421
381927
241
23794

A randomised backtracking solver fills a complete 9×9 grid, then clues are removed one at a time. After every single removal a counting solver re-checks the grid, and any removal that would allow a second solution is undone immediately — so the puzzle you see always has exactly one answer. The printable download puts the puzzle on page one and the answer key on page two. Everything is generated in your browser.

What is the Sudoku Generator?

Every puzzle this tool produces has exactly one solution — not most of them, all of them. A randomised backtracking solver first fills a complete, valid 9×9 grid.

  • Uniqueness verified after every single clue removal
  • Four difficulty levels from easy to expert
  • Given clues and solved cells shown in different weights
  • Reproducible from a seed you can save or share
  • Printable HTML with the answer key on its own page
  • Copy as text or download as TXT, entirely offline

How to use the Sudoku Generator

  1. 1

    Choose a difficulty from easy through to expert.

  2. 2

    Press New puzzle for a fresh grid, or type a saved seed to rebuild an old one.

  3. 3

    Check the Solutions stat reads Exactly 1 before you start solving.

  4. 4

    Tick Show the completed answer grid when you want to check your work.

  5. 5

    Download the printable file for the puzzle plus a separate answer key page.

About the Sudoku Generator

Every puzzle this tool produces has exactly one solution — not most of them, all of them. A randomised backtracking solver first fills a complete, valid 9×9 grid. Clues are then removed one at a time, and after each removal a counting solver re-checks the grid. If taking a clue away would allow a second solution, that clue is put straight back before the next one is tried.

That guarantee matters, because a sudoku with two solutions cannot be solved by logic alone — at some point you would have to guess. Four difficulty levels set how many clues to aim for, from a gentle 42 down to an expert 24, and the tool reports the clue count it actually achieved along with a confirmation that the solution is unique.

Puzzles are reproducible from their seed, so you can rebuild the same one later or share a seed with a friend to race the same grid. The printable download puts the puzzle on page one and the answer key on page two. Everything is generated in your browser and nothing is uploaded.

Frequently asked questions

Does every generated sudoku have only one solution?

Yes, and it is enforced rather than assumed. After each clue is removed a solver counts the solutions, and any removal that would create a second one is immediately undone. The Solutions stat on screen confirms it for the puzzle you are looking at.

What makes a sudoku easy or hard?

Mostly the number of clues given. More clues means more cells you can fill by simple elimination. Fewer clues force you into chains of deduction across rows, columns and boxes. This tool targets roughly 42 clues for easy and 24 for expert.

What is the minimum number of clues a sudoku can have?

Seventeen. It was proven by exhaustive computer search in 2012 that no valid sudoku with a unique solution can have sixteen or fewer clues. The expert setting here aims for around 24, which is already very demanding.

Can I print the puzzle and the answers?

Yes. The Printable download is a clean HTML file with the puzzle grid on the first page and the completed answer key on a second page, so you can print both and keep the key aside until you need it.

Can I get the same puzzle again later?

Yes. Note the seed shown in the seed box. Typing that seed with the same difficulty rebuilds the identical puzzle, which is handy for sharing a specific grid with someone else.

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