1 vs 1 sudoku duel: the same board, and the first to finish wins

By Miguel Arechaga

Playing sudoku online has always looked the same: you, a grid and a timer. The 1 vs 1 duel replaces that picture with a very different one: the same sudoku for two people at once, and whoever finishes first wins.

How a duel works

You press the ⚔️ Duel button and wait for an opponent. When someone turns up, the server sends exactly the same puzzle to both of you. Not a similar one, not one of the same difficulty: the same one, cell by cell.

From there it's a race. Each of you solves it on your own screen, and the first to submit a correct grid wins.

Neither of you picks the puzzle

That's not a small detail. If you could request the board, you could keep requesting until an easy one came up. The server picks it and imposes it, and that's what makes the duel mean something.

There are no hints

In a normal game you get a limited number of hints. In a duel there are none, for either player. It's the only way the comparison is fair: if one of you could uncover three cells and the other couldn't, you wouldn't be playing the same game.

Your opponent never sees your board

During the duel you see a bar telling you how many cells your opponent has filled. That's all that travels: a number. Your grid is never sent, and theirs never reaches you.

That's deliberate: the bar gives you the tension of the race without turning the duel into copying.

Who decides the winner

The server, not your browser. When you submit the grid, it's checked against the solution only the server knows — and so is the time: the clock that counts is theirs, not your computer's.

Put another way: there's nothing you can do from the browser console that wins you a duel. If you want to understand why that matters, read about how sudokus are generated and where each board's solution actually lives.

You're matched with players at your level

The matchmaking queue looks at your level before pairing you with anyone. If you've only been waiting a moment it looks for someone close to you; as the seconds pass it widens the band so you're not left without a game.

A beginner against someone with a thousand sudokus behind them isn't a duel: it's discouraging for one and a formality for the other.

If you lose, finish the game anyway

Losing the duel doesn't cancel what you played. The game still counts towards your daily streak, your XP and your stars on the Master's Path. Finishing the sudoku after your opponent has won isn't a consolation prize: it's exactly the same progress as if you'd played it alone.

You can also give up if it clearly isn't happening, and if nobody shows up after a while the search cancels itself.

Where you can play it

In classic sudoku and in all 26 variants: killer, diagonal, jigsaw, windoku, sandwich, kropki and the rest. The classic duel also has its own page, with the puzzle served on the spot.

If you've never tried a variant, a duel is a surprisingly good way in: the extra rules stick much faster when there's someone on the other side. Here's a run through the best known sudoku variants.