sudokly
Sudoku tool

Sudoku Checker

Is your sudoku a real one? Paste it in to find out if it's valid, has one solution, or none. Useful for puzzles you've copied from a book or made yourself.

How to use it
  1. Type the puzzle
    Fill in the cells with the numbers as given. Leave the empty cells blank.
  2. Check
    We'll tell you one of three things: it's valid and has one solution; it has no solution (a duplicate somewhere); or it has more than one (not really a sudoku).
  3. Fix and retest
    If something's off, edit the cells and check again. Conflicts will be highlighted in red.

Checker FAQ

What does 'valid' mean here?

A valid sudoku has no duplicates in any row, column, or 3×3 box, and has exactly one solution. Both conditions need to be true.

What if my puzzle has more than one solution?

Then it's not technically a sudoku. A real sudoku has exactly one answer. Add more given clues until that's true.

What if it has no solution?

That usually means a typo. two of the same number in a row, column, or box. Look for the highlighted cells and fix them.

Does the checker tell me the answer?

No, just whether the puzzle works. Use the solver if you want the full solution.