Building a puzzle takes a moment

The solution count is recomputed after every removed digit. Hard puzzles remove more digits and therefore need more checks. Skipping it would let multi-solution grids through, so the wait is the side we accept.

Can I see the solution?

No. A reveal button gets pressed at every dead end, and then the puzzle has not really been solved. When stuck, try the "only one home" view across rows, columns and boxes.

Can I close it and come back?

Yes. The grid, your entries and the elapsed time are stored on this device, so reopening resumes where you left off. Starting a new puzzle clears the save.

Can anyone see my times?

No. Fastest times are stored per difficulty in this browser only. There is no leaderboard and no account.

Does it work offline?

Yes. Generating and solving both happen entirely inside the browser.

Look for a cell with only one candidate

For an empty cell, cross off every digit already present in its row, column and box. Sometimes exactly one survives. This is the most basic move and carries almost all of an easy puzzle. Scanning the fullest rows, columns and boxes finds them far faster than sweeping the whole grid.

Then look for a digit with only one home

The reverse view. Take a 3x3 box missing a 7, then check its empty cells one by one: "not here, that row already has a 7". Often only one cell survives. When the first technique stalls, this is always the next thing to try — harder puzzles are solved by alternating between the two.

Pencil marks help, even mental ones

On paper you would write small candidates in the corners; working purely in your head means recomputing the same eliminations repeatedly. There is no pencil-mark feature here, but selecting a cell highlights every other cell holding the same digit, which is useful for seeing at a glance where a digit already lives.

You never need to guess

Because every puzzle is verified unique, logic alone reaches the end. Being stuck means there is a technique you have not applied yet — most often the "only one home" view, which is easy to miss. Try it across rows, columns and boxes before assuming otherwise.

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Sudoku

Runs in your browserNothing is uploaded

Every row, column and 3x3 box takes the digits 1 to 9 exactly once. Every puzzle served here has exactly one solution, so guessing is never required. There is no timer.

Seconds

Empty cells

Fastest

—

Building a puzzle…

Tap a cell, then pick a number. With a keyboard: arrows to move, 1-9 to enter, Backspace to erase

No time recorded at this difficulty yet

A digit repeated in its row, column or 3x3 box turns red. Clear the conflicts and fill all 81 cells.

All tools

Why this one

Only single-solution puzzles: Every time a digit is removed while building the puzzle, the number of solutions is recounted. If removing it would allow two, the digit goes back. Puzzles carved out at random can have several solutions, and those cannot be reasoned to an answer — they need a guess. Whether the game works at all rests entirely on this check.
Completion is not checked against an answer key: A grid is solved when all 81 cells are filled and nothing repeats in any row, column or box. It is never compared with the stored solution. Because the puzzle is guaranteed unique, any consistent filling must be that solution — whereas comparing against a key would tell someone they were wrong for finding a genuine alternative.
Conflicts show immediately: A digit that repeats in its row, column or box turns red as soon as you enter it. Hiding mistakes until the end means hunting for a cell you filled ten minutes ago. What it will not tell you is whether a digit is correct — that would be solving it for you.

How to play

Select a cell
Tap an empty cell to select it. Bold digits are givens and cannot be changed.
Enter a digit
Use the number pad below, or press 1-9 on a keyboard. Pressing the same digit again clears the cell, and arrow keys move the selection.
Fill all 81 cells
When every row, column and box holds 1 to 9 exactly once, the puzzle is solved. Conflicting digits appear in red.

How to make progress

Look for a cell with only one candidate: For an empty cell, cross off every digit already present in its row, column and box. Sometimes exactly one survives. This is the most basic move and carries almost all of an easy puzzle. Scanning the fullest rows, columns and boxes finds them far faster than sweeping the whole grid.
Then look for a digit with only one home: The reverse view. Take a 3x3 box missing a 7, then check its empty cells one by one: "not here, that row already has a 7". Often only one cell survives. When the first technique stalls, this is always the next thing to try — harder puzzles are solved by alternating between the two.
Pencil marks help, even mental ones: On paper you would write small candidates in the corners; working purely in your head means recomputing the same eliminations repeatedly. There is no pencil-mark feature here, but selecting a cell highlights every other cell holding the same digit, which is useful for seeing at a glance where a digit already lives.
You never need to guess: Because every puzzle is verified unique, logic alone reaches the end. Being stuck means there is a technique you have not applied yet — most often the "only one home" view, which is easy to miss. Try it across rows, columns and boxes before assuming otherwise.

FAQ

Building a puzzle takes a moment: The solution count is recomputed after every removed digit. Hard puzzles remove more digits and therefore need more checks. Skipping it would let multi-solution grids through, so the wait is the side we accept.
Can I see the solution?: No. A reveal button gets pressed at every dead end, and then the puzzle has not really been solved. When stuck, try the "only one home" view across rows, columns and boxes.
Can I close it and come back?: Yes. The grid, your entries and the elapsed time are stored on this device, so reopening resumes where you left off. Starting a new puzzle clears the save.
Can anyone see my times?: No. Fastest times are stored per difficulty in this browser only. There is no leaderboard and no account.
Does it work offline?: Yes. Generating and solving both happen entirely inside the browser.

Related tools

Why this one

How to play

Select a cell

Enter a digit

Fill all 81 cells

How to make progress

FAQ