Sudoku you solve together, on one board
How to play Sudoku with a friend
- Start a co-op gameChoose Sudoku and invite a friend. You'll both land on the same board.
- Agree who takes whatThere are no turns, so decide out loud — top half and bottom half, or one of you on rows and the other on boxes.
- Fill cellsTap an empty cell and enter a digit. The given clues are fixed and can't be changed by either player.
- Watch their entries landAnything your partner types appears on your board immediately. Their progress is your information.
- Finish the gridThe board completes when every cell matches the solution. There's no loser and no rating change — co-op games are deliberately unrated.
This is the opposite of racing two copies
There are two completely different things people mean by "Sudoku with a friend", and they feel nothing alike.
Racing means two separate grids and a timer. It's a competition, it's fine, and it's basically solo Sudoku with a scoreboard bolted on — you never actually interact.
Co-op means one grid. Your partner's deduction changes your board while you're looking at it. That turns a silent puzzle into a conversation, which is the entire reason it's built this way here.
How to split a board between two people
Because there are no turns, two people can absolutely trip over each other — both staring at the same box, both ignoring the same corner.
The split that works best is by region, not by technique. Take a half each, or three boxes each with the middle shared. You'll naturally hand cells over as one side opens up.
The split that works worst is by difficulty: "you do the easy ones" leaves one person idle and the other doing the whole puzzle with an audience.
Say the digit out loud when you place it. A shared board with silence is two people solving the same puzzle in parallel; a shared board with talking is one person with two brains.
Why co-op games don't move your rating
Every competitive duel here updates a Glicko-2 rating, the same family of system competitive chess uses. Co-op games don't, and that's deliberate rather than unfinished.
A rating measures one player against another. In a co-op solve there is no loser to take points from — the server skips the rating update entirely for games with no losing side.
It also keeps the incentives clean. Nobody should be reluctant to help their partner because it might cost them a number.
Three things that actually help
- Claim a region out loud before you start. Two people quietly solving the same box is the most common way a co-op solve stalls.
- When you get stuck, say what you've ruled out rather than what you're looking for. Eliminations transfer between brains; hunches don't.
- Let your partner finish the box they started even if you spot it first. Snatching the last cell of somebody's box is technically optimal and socially fatal.
Sudoku questions
Can you play Sudoku with a friend?+
Yes, in two very different ways. You can race separate copies of the same grid, or you can share one grid and fill it together. Co-op Sudoku here is the shared-grid kind: one board, both players typing into it live, no turns.
Do we take turns?+
No. Either player can fill any empty cell at any moment. That's what makes it collaborative rather than alternating, and it's why agreeing on who takes which region matters.
Can my partner overwrite what I entered?+
The original clues are locked for both of you. Cells you've filled in can be changed, which is a feature — catching each other's mistakes is most of what co-op solving is for.
Does a co-op Sudoku win affect my rating?+
No. Co-op games are unrated on purpose, because a rating compares two players and a shared solve has no losing side.