Sudoku FAQ
Short answers about the puzzles on sudokuprint.app: how levels are graded, why every puzzle has exactly one solution, what the puzzle codes do, how to print and save PDFs, what happens to your data, and a few facts about sudoku itself, such as the fewest clues a puzzle can have.
Sudoku questions
Is sudokuprint.app free?
Yes. The generator, the PDF download, the daily puzzles and the answer keys are free. There is no account, no sign-up and no limit on how many puzzles you make. There is no advertising on the site at the moment.
Does every puzzle have exactly one solution?
Yes. After each number is removed, a solver counts the solutions and stops at two. If a second solution appears, the number is put back. We tested this on 1,000 generated puzzles per level.
How are the levels decided?
A step-by-step solver uses human techniques in order from simple to advanced. Easy needs only singles, medium needs pairs or pointing pairs, hard needs triples or an X-Wing, and expert needs swordfish, XY-Wing or more.
What is the puzzle code for?
The code, such as #H-01234, rebuilds exactly the same puzzle and answer. Type it into Open code. It is printed above each grid and next to each answer, so you can match them and share a puzzle with a friend.
Why does it take a while to make hard puzzles?
Each new puzzle is tested many times, by a solution counter and by the grader. Hard and expert puzzles are rarer, so the generator tries more grids. Several processor cores are used at once if your device has them.
Can I use the puzzles in class or a club?
Yes, you may print and copy the puzzles for personal use, classes and clubs. Please do not sell them as your own puzzle book. If you are unsure, write to info@sudokuprint.app.
Do you store my puzzles or my answers?
No. Everything is made and solved in your browser. If you play on screen, your entries are kept in your own browser’s storage on this device. Nothing is sent to a server.
Why does my printout look small?
Check that your print window is set to 100% or actual size, not "fit to page" with large margins. Choose fewer puzzles per page, or use the large print page for one big puzzle per sheet.
Does it work on a phone or tablet?
Yes. You can make puzzles, download the PDF and play on screen. On a phone, use Download PDF and then share or print the file with your phone’s print option.
What is the fewest clues a sudoku can have?
A 9×9 sudoku with exactly one solution needs at least 17 given numbers. Gary McGuire and colleagues proved this in 2012 with a large computer search. The puzzles here have more, because few-clue puzzles are rare.
Last updated: October 15, 2026