Sudoku solver with step-by-step explanations
Enter the digits from any Sudoku. Solve gives the answer in a blink. The step-by-step mode shows how a human would solve it, one technique at a time.
Type or paste your puzzle, then press Solve. The solver checks the grid for conflicts, finds the solution, and tells you if the puzzle has no solution or more than one. For a lesson instead of the answer, use step by step.
Type the digits you know, leave the rest empty and press Solve. You can also paste 81 characters from a text file.
Walk through the puzzle one logical step at a time. Each step names the technique, shows the cells involved and links to its guide.
Two ways to use it
Solve finds the full solution at once. It also tells you whether the puzzle is valid: a proper Sudoku has exactly one solution, so the solver reports zero, one or several.
Step by step is for learning. It works out the candidates for every cell, then finds the easiest technique that makes progress, names it, highlights the cells involved and explains what it removes or places. Press Apply to make the move and ask for the next one. It knows all twelve techniques on our techniques page.
Entering a puzzle
- Click a cell and type a digit from 1 to 9. The cursor moves on by itself. Arrow keys move around.
- To paste a puzzle, copy 81 characters (digits, with 0 or a dot for empty cells) and paste into any cell.
- You need at least 17 digits. No valid Sudoku has fewer clues, as explained in why a Sudoku has one solution.
When the step-by-step mode says it is stuck
Some very hard puzzles need techniques beyond the twelve we cover, such as long chains. The solver then says so honestly. Press Solve to get the answer, and study the position to see what you missed.
Use it to learn, not just to finish
Looking at an answer teaches little. Looking at the technique teaches a lot. When you are stuck, ask for one step, read which pattern it found, then go back to your own puzzle and look for the same pattern. See also how to solve Sudoku.
Frequently asked questions
Is the solver accurate?
Yes. It uses an exhaustive search that checks every possibility, so it finds the solution if one exists and tells you if there are none or several.
Can it solve a puzzle I photographed?
Not yet. You enter or paste the digits yourself.
Why does it say my puzzle has more than one solution?
The grid is not a proper Sudoku: some clues are missing or mistyped. Check the digits against your source.
Does the solver store my puzzle?
No. Everything runs in your browser and nothing is sent anywhere.