solution lookup
Sudoku answers — look up the solution to any puzzle
Stuck on a grid, or checking a finished one? Type the code printed under the puzzle and its solution comes straight back. No answer key needed, and no account.
How a six-character code knows the answer
This is the part that usually raises an eyebrow, because there is no database here and your puzzle was never uploaded anywhere. The trick is that the code is not a reference to a stored puzzle. It is the puzzle, in compressed form.
Generating a sudoku involves a lot of shuffling: which digits go where in the first complete grid, and which order the clues are taken out in. All of that shuffling is driven by a single starting number. Fix that number and the whole process runs the same way every time, down to the last cell. So the code carries two things — which difficulty was asked for, and that starting number — and from those the generator rebuilds your exact puzzle, and therefore its exact solution, on the spot.
Two useful consequences. There is nothing to expire: a sheet you print today will still look up in ten years, because the answer is recomputed rather than retrieved. And there is nothing to leak: the lookup runs in your browser like everything else on this site, so no one, including us, learns which puzzles you have been working on.
The codes are deliberately awkward to mistype. They never use the letters I, L, O or U, so there is no confusing them with 1 and 0, and each code carries a small check built into it. Get a character wrong and you are told the code is wrong — rather than being handed a different puzzle’s answer and left to wonder why nothing lines up.
Where to find the code
Look directly beneath the grid. Each puzzle prints its code on the left — a hash followed by six characters — with the difficulty and clue count on the right. On a sheet with four or six puzzles to a page, every grid has its own, so you can look up one puzzle without spoiling the rest of the page.
If you would rather have the answers on paper from the start, the generator can print them for you: see printable sudoku with answers, which puts a full key at the back of the PDF. This page is the fallback for when you did not print one, or no longer have it to hand.
Looking up answers — questions
Where do I find the puzzle code?
It is printed directly under the grid, just left of the difficulty. Six characters after a hash, like #K7M2A9. Every puzzle on every sheet carries its own.
How can it know the answer without storing my puzzle?
Because the code is not a reference to a stored puzzle — it is the recipe for one. The generator turns a code into a grid by a fixed procedure with no randomness left in it, so feeding the same code back in rebuilds exactly the same puzzle, and its solution, from scratch. Nothing was ever uploaded and nothing needed to be kept.
Does this work for a sheet I printed months ago?
Yes. There is no expiry and no database to go stale — the code is all that is needed. A sheet found at the back of a drawer in five years will still look up, as long as the code is legible.
It says the code is not one we could have printed. What now?
Almost always a misread character. The codes never contain the letters I, L, O or U, precisely so they cannot be confused with 1 and 0 — so if you read one of those, try the digit instead. The check built into every code means a wrong entry is rejected rather than quietly returning somebody else’s puzzle.
Can I still get the answers printed in the PDF?
Yes, that has not gone anywhere. Tick "Include answers" in the generator and the solutions come as a section at the back of the document. It is off by default, since most people would rather have a clean set of puzzles and look up the odd answer here. This page is for exactly that.
Can I link straight to a solution?
Add the code to the address: /sudoku-answers?code=K7M2A9 opens with that puzzle already worked out. Handy if you are setting puzzles for other people and want to hand them the answer separately.
Need more puzzles?
The free printable sudoku generator will make you a fresh set at any difficulty, and you can now mix levels in one run. If you are checking a grid because you got stuck rather than because you finished, the solving techniques guide may get you moving again without giving the whole thing away.