Printable Sudoku, each one proven
Generate a sheet of puzzles with answer keys. Every puzzle is checked to have exactly one solution before it reaches the page, and its difficulty is measured from the techniques it actually needs.
Generate a sheet
Generated on this device — nothing is uploaded
Why generating expert puzzles takes longer
Clues are removed from a completed grid in a random order, and after every single removal the remaining grid is re-solved from the givens alone to confirm exactly one solution still exists. That is the slow, boring way to do it, and the only way that actually guarantees what it claims — the check never consults the solution the puzzle was carved from, so it cannot be fooled by already knowing the answer.
The difficulty that emerges from a carve is not chosen; it is whatever the removals happen to produce. So the generator carves, measures, and discards anything outside the band you asked for. Beginner and easy turn up constantly. Expert turns up in roughly one carve in a hundred, which is why it takes a moment and why it uses asymmetric carving — measured over 120 grids, symmetric carving produced no expert puzzles at all.
Symmetric grids look better on paper and are used for everything up to hard. They cost a little strict minimality: because clues leave in mirrored pairs, a clue whose mirror is essential stays even where it could go on its own. Uniqueness is unaffected.
For classrooms and puzzle books
Every sheet prints two puzzles to a page with the answer keys on their own pages at the end, so a set can be handed out without the answers travelling with it. Nothing about the sheet leaves your machine — no account, no upload, no watermark, and no limit on how many you make or what you do with them.
The seed field is there for when you need the same sheet twice. Type anything memorable, and that sheet is reproducible forever: same puzzles, same order, same answers. Useful for printing a replacement copy a week later, or for giving two classes identical work.
What the difficulty labels mean here
They are measured, not guessed from clue count. A second solver works the way a person does — naked singles, hidden singles, pointing pairs, box/line reduction, naked and hidden pairs, triples, X-wings — and the label comes from the hardest technique the puzzle genuinely requires.
This matters for teaching. A sheet labelled beginner is solvable start to finish by looking for cells with only one digit left, which is exactly what you want when introducing the rules. An easy sheet forces the next idea — scanning for a digit with only one home left in a unit. Nothing here ever needs guessing, at any level.
Clue count would not give you that. We have generated two puzzles with 31 clues each, one beginner and one easy: same count, genuinely different work.
Related
Play Sudoku here, with hints that explain the next deduction rather than filling it in.
Questions people actually ask
Are the puzzles really unique?
Yes, and it is verified rather than assumed. After every clue removed during generation, the remaining grid is solved again from the givens alone and the removal is undone unless exactly one solution remains. A solver finding an answer proves only that at least one exists; proving uniqueness means continuing the search and finding no second.
Can I use these in a classroom or sell a puzzle book?
Yes. They are generated on your machine from a seeded algorithm, there is no account, no watermark and no usage limit. What you print is yours.
Will the same seed give the same sheet?
Always. Type a seed you will remember and that sheet is reproducible: same puzzles, same order, same answers. Useful for reprinting a lost copy or giving two classes identical work.
Why did one puzzle get skipped?
Because it could not reach the requested band within the time budget. The generator skips it rather than including a puzzle carrying a label it did not earn — an 'expert' sheet with an easy puzzle in it is worse than a sheet with five puzzles.
Do students ever have to guess?
No, at any difficulty. A puzzle that cannot be completed using the modelled techniques is discarded during generation rather than shipped as 'expert'. Every puzzle on the sheet is solvable by pure deduction.
Where do the answer keys print?
On their own pages after all the puzzles, so a sheet can be handed out without the answers going with it.