--- title: "Sudoku Solver, Step by Step with Explanations | Sudoku Flow" description: "Free Sudoku solver that shows every step: type in a puzzle or take a photo of it, and see each move with its technique explained." url: https://sudokuflow.com/tools/sudoku-solver/ language: en --- # Sudoku solver, step by step Type in a puzzle, or take a photo of it, and press Solve step by step. The solver finds every move a person would make, from the first easy number to the last, using logic only. It names the technique of each step, highlights the squares that prove it and explains it in plain words, so you can follow along or stop at the step where you got stuck.
Paste a puzzle 81 characters, row by row: 1 to 9 for numbers, 0 or a dot for empty squares. They load as puzzle numbers.
## Quick answer Type the puzzle's numbers into the grid, or scan a photo of it, and press Solve step by step. The solver works out the answer with logic only and lists every step in order with the technique it uses: singles first, then pairs, X-Wings, wings and chains. Open a step to see the squares that prove it and the explanation, the same one the hint in our app gives. It also rates the puzzle by its hardest step, on our app's six levels from Easy to Extreme. Everything runs in your browser: nothing you type and no photo you scan is sent anywhere. Your puzzle is kept on this device until you clear it. ## Filled in part of it already? The Sudoku checker tells you how many of your numbers are wrong and where, and its Next step starts from your own grid. [Sudoku checker →](https://sudokuflow.com/tools/sudoku-checker/) ## How to use it 1. Type the puzzle's numbers: tap a square, then a number. Or scan a photo of the puzzle, or paste it as 81 characters. 2. Press Solve step by step. The list below the grid shows every step in order. 3. Open a step to see it on the board and read why it works. Apply moves on to the next step. ## How the solver works On each step, the solver looks for the easiest technique that places a number, the way a person would: a square with only one number left, a number with only one place in a row, column or box, then pairs, X-Wings, wings and chains. It is the hint engine of our app, so the steps and the words are the ones the app uses. It does not guess. Only a few of the hardest puzzles need a forcing chain, where one candidate is tried and followed until it breaks, and the solver says so when a step is one of those. [How the solver reads a photo, step by step →](https://sudokuflow.com/tools/sudoku-solver/how-it-works/) ## What the rating means The rating is the level of the hardest step, on the six levels of our app. These are the techniques that set each level: - **Easy**: [Last Remaining Cell](https://sudokuflow.com/lessons/lastRemaining/), [Nearly Complete](https://sudokuflow.com/lessons/nearlyLastRemaining/), and [Naked Single](https://sudokuflow.com/lessons/nakedSingle/) - **Medium**: [Hidden Single](https://sudokuflow.com/lessons/hiddenSingle/) - **Hard**: [Pointing Pair](https://sudokuflow.com/lessons/pointingPair/), [Pointing Triple](https://sudokuflow.com/lessons/pointingTriple/), [Box/Line Reduction](https://sudokuflow.com/lessons/boxLineReduction/), [Naked Pair](https://sudokuflow.com/lessons/nakedPair/), [Hidden Pair](https://sudokuflow.com/lessons/hiddenPair/), [Naked Triple](https://sudokuflow.com/lessons/nakedTriple/), and [Hidden Triple](https://sudokuflow.com/lessons/hiddenTriple/) - **Expert**: [X-Wing](https://sudokuflow.com/lessons/xWing/), [Naked Quad](https://sudokuflow.com/lessons/nakedQuad/), [Hidden Quad](https://sudokuflow.com/lessons/hiddenQuad/), [Swordfish](https://sudokuflow.com/lessons/swordfish/), [Y-Wing](https://sudokuflow.com/lessons/yWing/), [Skyscraper](https://sudokuflow.com/lessons/skyscraper/), [Simple Coloring](https://sudokuflow.com/lessons/simpleColoring/), and [Empty Rectangle](https://sudokuflow.com/lessons/emptyRectangle/) - **Master**: [XYZ-Wing](https://sudokuflow.com/lessons/xyzWing/), [Two-String Kite](https://sudokuflow.com/lessons/twoStringKite/), [Grouped Two-String Kite](https://sudokuflow.com/lessons/groupedTwoStringKite/), [W-Wing](https://sudokuflow.com/lessons/wWing/), [X-Chain](https://sudokuflow.com/lessons/xChain/), [XY-Chain](https://sudokuflow.com/lessons/xyChain/), [WXYZ-Wing](https://sudokuflow.com/lessons/wxyzWing/), and [Remote Pairs](https://sudokuflow.com/lessons/remotePairs/) - **Extreme**: [BUG+1](https://sudokuflow.com/lessons/bugPlusOne/), [Unique Rectangle](https://sudokuflow.com/lessons/uniqueRectangle/), [Finned X-Wing](https://sudokuflow.com/lessons/finnedXWing/), [Jellyfish](https://sudokuflow.com/lessons/jellyfish/), [Finned Swordfish](https://sudokuflow.com/lessons/finnedSwordfish/), [ALS-XZ](https://sudokuflow.com/lessons/alsXZ/), [ALS-XY-Wing](https://sudokuflow.com/lessons/alsXYWing/), [Sue de Coq](https://sudokuflow.com/lessons/sueDeCoq/), and [3D Medusa](https://sudokuflow.com/lessons/medusa3d/) [What each Sudoku difficulty level asks of you →](https://sudokuflow.com/data/sudoku-difficulty-levels/) ## Questions ### Can it solve any Sudoku? Any classic 9 by 9 Sudoku with exactly one answer. If the numbers you type have no answer or more than one, it says so instead of guessing which one you meant. ### Can it read a puzzle from a photo? Yes. Press Scan a photo and take a picture of the puzzle, or pick a screenshot. The photo is read on your device and never uploaded. Check the numbers it reads before you solve: the squares it is less sure of are marked. ### Why step by step and not just the answer? The answer alone does not help with the next puzzle. Each step shows the pattern that made it possible, so next time you can spot it yourself. Show the solution is there when you only need the answer. ### Is it free? Yes, with no sign-up. It runs in your browser, so the puzzle you type stays on your device. ![Sudoku app icon](https://sudokuflow.com/assets/app-icon.png) ## Want more boards like this? We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number. [App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_web&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dweb%26utm_campaign%3Dsite) Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.