How to play
One rule, applied three ways: each of the nine rows, each of the nine columns and each of the nine heavy-bordered boxes must end up holding every digit from one to nine, with nothing repeated. The digits printed when the puzzle is dealt are the givens and cannot be changed; everything else is yours to fill in. There is no arithmetic anywhere in Sudoku — the symbols could be nine colours and the puzzle would be identical.
The counter marked Empty is the honest progress bar: it drops as you commit digits and it is the number to watch when you feel stuck, because a grid that has not changed in two minutes usually means you are re-reading the same three cells. Time starts on your first entry, not on page load, so opening the puzzle and walking away costs you nothing.
What each button is for
- Check marks the entries that conflict with the solution. Use it when you suspect you went wrong ten moves ago and do not want to unwind the whole grid by hand.
- Clear my entries wipes what you wrote and leaves the givens alone, which is the clean restart of the same puzzle rather than a new one.
- Reveal solution exists for the evening when a grid has beaten you. It does not record a time, and there is no penalty attached to it beyond the obvious one.
- New puzzle deals a fresh grid at the current difficulty and resets the clock.
What the four difficulties actually change
Difficulty in Sudoku is not about clever rules appearing at higher levels; the rules never change. What changes is how many digits you start with, and therefore how deep you have to reason before the next certain cell appears. Here the counts land at roughly 43 givens on Easy, 36 on Medium, 31 on Hard and 25 on Expert, and the exact number for the grid in front of you is announced when it is dealt.
The reason the number varies slightly is worth knowing, because it is the guarantee that makes the puzzle fair. The generator starts from a complete solved grid and takes digits away one by one, counting after each removal how many solutions the remaining grid admits and stopping that count at two. If removing a digit would allow a second valid answer, that digit goes straight back. Digging stops when the target is reached or when no further removal is safe — so every puzzle on this page has exactly one solution and can be finished by reasoning alone.
In practice that means Easy and Medium can be solved end to end by scanning: find the cell where only one digit is possible, write it, and repeat. Hard and Expert eventually stop offering those cells, and you have to work with pairs — two cells in a box that can only hold a 4 and a 7 between them, which removes 4 and 7 from every other cell that shares a line with both. That is not guessing. It is the same certainty, just two steps further along.
Typical completion times from our own play testing, as estimates and nothing more: four to eight minutes on Easy, eight to fifteen on Medium, fifteen to thirty on Hard, and Expert anywhere from twenty minutes to a puzzle you leave open and come back to. Comparing your time against your own previous best on the same level is the only comparison that means much.
A note on pencil marks
There is deliberately no notes mode on this board. Adding one would mean a second layer of taps for every cell, and on a phone it turns a calm puzzle into fiddly work. If you are on Hard or Expert and want to track candidates, a scrap of paper beside the screen is faster than any interface we tried: write the cell coordinates and the two or three digits still in play, and cross them out as lines get resolved. Most players find they only need it for four or five cells in a whole grid.
Where the puzzle came from
Number placement puzzles on a nine-by-nine grid appeared in French newspapers in the late nineteenth century, but the modern form was published as Number Place in the American magazine Dell Pencil Puzzles and Word Games in 1979; the design is credited to Howard Garns, a retired architect from Indiana. The Japanese publisher Nikoli picked it up in 1984 and gave it the name that stuck, later adding the conventions of symmetric givens and a limited count of them.
The worldwide wave came in 2004, when Wayne Gould, a retired judge from New Zealand, wrote a program to generate grids and convinced The Times in London to print them. Within a year the puzzle was in newspapers on every continent. What runs on this page was built here from nothing: the rules are shared property, but neither the code nor a sentence of the text is copied from anywhere.
Questions players ask
Can a puzzle here have two answers?
No. A given is only removed if the grid still has exactly one solution afterwards, which is tested by counting solutions and stopping at two.
How many givens per difficulty?
About 43 on Easy, 36 on Medium, 31 on Hard, 25 on Expert. The exact figure is announced when the grid is dealt.
Do I ever have to guess?
No. On Hard and Expert you may need to carry two possibilities for a cell and follow each until one produces a contradiction, but the answer is always reachable by reasoning.
Are my times uploaded anywhere?
No. Best times live in this browser only, under keys starting with bg:, and clearing
your browsing data removes them.