One solution
Nine diagonal cells are removed from a completed grid. Each row is missing exactly one number, so there is only one way to finish it.
Sudoku tools / Solver
Sudoku solver & checker.
Check a Sudoku for conflicting clues, no solution, multiple solutions, or one unique answer. Enter the numbers by hand or paste an 81-cell puzzle.
Calculations run in your browser. No account required.
Your puzzle
63 clues · 18 empty cellsKeyboard: arrow keys move; 1–9 enter a clue and move to the next empty cell; 0, Delete or Backspace erase. Home/End move within a row. Ctrl/⌘ + Z undoes; Shift + Ctrl/⌘ + Z redoes. Tab leaves the grid.
Ready when you are
Enter your clues, then check whether the puzzle has exactly one solution.
Use 1–9 for clues and 0 or . for empty cells, row by row from the top left. Spaces, line breaks and grid separators are ignored.
Import replaces the grid. Undo restores the previous clues.
Try it yourself
Four examples. Four different results.
Load an example into the grid, then select Check puzzle. Each example is constructed to demonstrate a specific result. Loading an example replaces your input; Undo brings it back.
Conflicting clues
The two 1s in row 1 repeat in the same row and box. Both conflicting cells are marked.
No solution
Row 1 needs a 9 in column 9, but that column already contains a 9. There are no repeated clues, yet no valid completion exists.
Multiple solutions
All 1s and 2s are removed from a completed grid. Swapping 1 and 2 gives different valid completions, so the remaining clues cannot select one answer.
How to check a Sudoku
- 01 / Enter
Copy the original clues
Enter the printed numbers and leave blank cells empty. To verify your own progress, you can include your filled numbers too; every entered number is treated as fixed.
- 02 / Check
Read the diagnosis
The checker first finds repeated numbers, then searches for valid completions. It stops after two solutions or a 15-second limit. An interrupted check gives no conclusion.
- 03 / Continue
Understand your next move
Correct a clue, copy a unique solution, or learn to work it out yourself with Sudoku candidates. This checker gives a complete answer, not a step-by-step logical proof.
Conflicting clues
The same number appears twice in a row, column, or 3 × 3 box. Correct the marked clues before checking again.
Read the guideNo solution
The clues contain no immediate duplicates, but they cannot all belong to a completed Sudoku. Recheck the numbers against your original puzzle.
Read the guideMultiple solutions
At least two valid completions fit the clues. A clue may be missing. The checker does not present an arbitrary completion as the answer.
Read the guideOne solution
Exactly one completed grid fits every entered number. The result preserves your clues and highlights the numbers added by the solver.
Read the guideSudoku solver questions
Can a Sudoku have no duplicates and still be impossible?
Yes. A duplicate is an immediate rule violation, but clues can also lead to an impossible position later in the search. The no-solution example above demonstrates this: row 1 needs a 9 in a cell whose column already has a 9.
Why won’t the checker show one answer when several exist?
Choosing one of several completions would hide the fact that the clues do not identify a unique answer. Check your transcription for missing numbers. A conventional Sudoku puzzle is intended to have exactly one solution.
Does this support diagonal, killer or other Sudoku variants?
No. This checker uses standard 9 × 9 Sudoku rules only: each row, each column and each 3 × 3 box must contain the digits 1–9 once. It does not enforce diagonals, cage totals or other extra constraints.
Is my puzzle sent to a solving service?
No. Checking happens in a Web Worker in your browser. A puzzle included in a page URL is part of that page request; manually typed or pasted clues are not sent to a solving service.