Play a friend
Every game here has a short link. Send it and the other person gets exactly the grid you are looking at — same clues, same answer — so the times are worth comparing.
Print a sheet of 0
Six moderate puzzles and their answers, on separate sheets so a puzzle cannot be spoiled by the page it is on.
The puzzles
The answers
What the link actually does
It carries a code like g0 or m1f: one letter for the difficulty, then the number of the puzzle. Open it and the board is built from that code, so two people on opposite sides of the world are working the identical grid rather than two of the same level.
That matters more than it sounds. Two Sudoku labelled "hard" can differ enormously in how long they take, so comparing times across different puzzles tells you nothing. Comparing them on one grid is the only version of the question worth asking.
The code is short enough to read down a phone or type by hand, and it never expires. The puzzle behind a code is fixed for as long as the site exists, because the library it points into is only ever added to, never reordered.
Coming back to a game
Keep the link and the grid is still there next week, with whatever you had already written in it. Progress is stored on the device you are using, so the same link opened on a phone starts clean and then remembers that phone separately.
That split is deliberate rather than a limitation to apologise for. A puzzle half-solved on a laptop is a different working state from the same puzzle on a phone, and merging them would mean choosing whose pencil marks to throw away.
If you want a clean run at a grid you have already touched, the clear button empties the board without changing the link.
What it does not do
It does not show you the other person's board while they work. Live shared state needs a server holding the game between two browsers, and this site is static files on a content network — there is nothing running to hold it.
So "playing together" here means the same puzzle, worked separately, then compared. That is the honest description of what the link does, and it is most of the value: the disagreement about who is quicker is settled by both people having faced identical clues.
Nothing is uploaded either. The code goes in the link, your progress stays in your own browser, and no account is involved at any point.
Common questions
How do I send someone the same Sudoku?
Press share on any game and you get a short link. Anyone who opens it gets the identical grid, with the same clues in the same squares.
Can we play at the same time and watch each other?
No. You both get the same puzzle and your own clock, then compare when you finish. Watching each other live would need a server, and this site has none by design.
Does a shared link expire?
No. The code points at a fixed puzzle in a library that is only ever added to, so a link sent today opens the same grid in a year.