Free Sudoku Solver with Step-by-Step Explanations

Use this Sudoku solver to enter, paste, or scan a classic 9×9 puzzle. Get a hint, full steps, or the final answer.Enter a classic 9×9 puzzle, paste 81 digits, or upload a clear image. This free online Sudoku solver can show the next logical move, guide you step by step, or reveal the completed grid when you only need the answer.

Free to use · No signup · Works on phone and desktop

Enter your Sudoku

Add the given numbers and leave empty cells blank.

Choose how this Sudoku solver helps

Use the Sudoku solver as a small nudge, a guided walkthrough, or a final answer checker. You stay in control of how much the puzzle reveals.

Choose how much help you get

Ask for one logical hint, follow the complete solution path, or reveal the finished grid only when you need it.

Understand every move

The Sudoku solver names each supported technique and highlights the cells that make the move valid.

Scan, review, then solve

Upload a screenshot or photo, correct any misread clues in the editable grid, and solve only the puzzle you approved.

Catch bad inputs early

The Sudoku solver flags duplicate clues and tells you when a puzzle has no solution or more than one solution.

How to use the Sudoku solver in four steps

Add

Type the givens, paste an 81-character string, or upload a clear image.

Check

Let the Sudoku solver mark conflicts, then correct any scan mistakes.

Choose help

Get one hint, follow the solution step by step, or reveal the final grid.

Continue

Use the highlighted cells and explanation to keep solving yourself.

5376195986863485317266284195879

Sudoku solver example

Naked Single · R5C5 = 5

R5C5 can only contain 5 after checking all of its connected cells.

The Sudoku solver highlights the target and the supporting cells that provide the evidence. It also names candidate eliminations when the next supported step is a Locked Candidate or Naked Pair.

How this Sudoku solver explains logical steps

An exact calculation can complete a valid Sudoku, but that does not make every calculation a useful human explanation. This Sudoku solver keeps validation and final completion separate from the learning view, which shows only supported techniques with visible evidence.

If the current position requires a technique the explainer does not support, the page says so instead of inventing a step. You can still reveal the exact final grid or return to the puzzle and continue on your own.

Supported at launch

Classic 9×9 Sudoku with 3×3 boxes, including Naked Singles, Hidden Singles, Locked Candidates, and Naked Pairs.

Not supported yet: Killer Sudoku, Samurai Sudoku, diagonal rules, irregular regions, or handwritten candidate notes.

Sudoku Solver FAQ

How does the Sudoku solver work?

The Sudoku solver accepts givens entered by hand, an 81-character puzzle, or a grid detected from an image. It checks the clues for rule conflicts, verifies that the puzzle has one solution, and can show one logical move, a step-by-step path, or the final grid.

Can this Sudoku solver read an image or photo?

Yes. Upload a clear screenshot or a straight, well-lit photo that includes the full grid. The detected digits appear in an editable 9×9 grid, so you can correct scan mistakes before solving. Image recognition is an input aid, not a guarantee; always review the clues first.

Does the Sudoku solver explain every step?

The Sudoku solver explains each supported logical technique, including the target cell and the evidence behind the move. If exact solving can finish the puzzle but the explainer cannot produce another supported human-style step, the page says so and offers the final grid instead.

What is the best Sudoku solver technique to start with?

Start with forced moves instead of guessing. Scan each 9-cell unit for a cell that has only one possible digit, then look for a digit that can appear in only one position within that unit. These are commonly called Naked Singles and Hidden Singles.

What is the 45 rule in Sudoku?

The digits 1 through 9 add up to 45. Every 9-cell unit in a classic Sudoku contains those digits once, so each unit also totals 45. This fact is especially useful in Killer Sudoku and other puzzles that include cage sums.

Is there a 1-5-9 rule in classic Sudoku?

Classic Sudoku has no universal 1-5-9 rule. Some variant puzzles use columns 1, 5, and 9 as indexers for the positions of digits 1, 5, and 9. Follow any special instructions printed with the puzzle; otherwise use the standard classic Sudoku rules.

What does the Sudoku solver do if my puzzle is invalid?

Duplicate givens are highlighted before solving. It also reports when a puzzle has no valid solution or more than one solution. Your original clues are never replaced, so you can edit the grid and try again.

Is this Sudoku solver a game or a Sudoku generator?

This Sudoku solver works with a puzzle you already have. It is not a daily game and it does not create new puzzles. To make a fresh printable 9×9 puzzle with an answer key, use the Word Puzzle World Sudoku Generator.