Type your puzzle into the grid, drop or paste an image of it (Ctrl+V works), or take a photo. Images are read on your device and never uploaded.
Sudoku Solver, Step by Step
Stuck on a sudoku? Enter it above and the solver shows you the next move the way a good player would find it. It names the technique, highlights the cells and explains why the move works, so you learn the pattern instead of just copying an answer.
Three ways to enter your puzzle
- Type it. Click a cell (or use the arrow keys) and type the digits. On a phone, tap a cell and use the number pad under the grid.
- Photo or screenshot. Press Solve from a photo or screenshot to pick an image or take a photo, drop an image onto the grid, or paste a screenshot with Ctrl+V. The solver finds the grid, corrects for a tilted camera, ignores pencil marks and reads the printed digits. Everything happens in your browser, and the image is never uploaded. The digits it read are outlined on the grid and your picture is shown underneath. Any that it was less sure of are outlined in orange. Tap a cell and type to fix it.
- Paste the digits. Press Paste digits and paste 81 characters, reading left to right and top to bottom, with
0or.for empty cells. Pasting a line like that anywhere on the page works too.
When a puzzle loads, the solver checks it straight away. It tells you whether it has exactly one solution, a clash between two digits, too few clues, or no solution at all (almost always one wrong digit).
Solving one step at a time
- Hint gives you a nudge without spoiling the move. It names the technique to look for and the row, column or box where it is.
- Show next step highlights the move on the board and explains it. Cells involved are shaded, digits being placed are green, and candidates being removed are red. Candidates appear automatically when a step needs them, and you can turn them on yourself with Show candidates.
- Apply step makes the move and moves on to the next one. Undo takes back the last step or edit.
- Solve all finishes the puzzle and rates it by the hardest technique it needed, from Easy to Extreme, with a count of every technique used.
Each step links to its technique guide, so if the solver uses something you haven’t met yet, such as a Skyscraper or a W-Wing, you can learn it there and then.
Techniques the solver uses
The solver always uses the simplest technique that makes progress, in this order:
| Technique | Level | What it does |
|---|---|---|
| Full House | Easy | Fills the last empty cell of a row, column or box |
| Hidden Single | Easy | A digit that fits in only one cell of a row, column or box |
| Naked Single | Easy | A cell with only one candidate left |
| Pointing Pair / Triple | Medium | A box’s candidates for a digit all on one line clear the rest of that line |
| Box/Line Reduction | Medium | A line’s candidates for a digit all in one box clear the rest of that box |
| Naked Pair | Medium | Two cells with the same two candidates lock those digits |
| Hidden Pair | Hard | Two digits that fit in only two cells clear the cells’ other candidates |
| Naked Triple / Quad | Hard | Pair logic over three or four cells |
| Hidden Triple / Quad | Hard | Hidden pair logic over three or four digits |
| X-Wing | Expert | A digit locked into two rows and two columns |
| Skyscraper | Expert | Two strong links on one digit that share a base |
| Two-String Kite | Expert | A row link and a column link joined in a box |
| XY-Wing | Expert | A two-candidate pivot and two wings |
| XYZ-Wing | Expert | An XY-Wing whose pivot has three candidates |
| W-Wing | Expert | Two matching pairs joined by a strong link |
| Swordfish | Expert | The X-Wing over three rows and columns |
| Simple Coloring | Extreme | Two-coloring a digit’s chain of strong links |
| Unique Rectangle | Extreme | Avoids a pattern that would give two solutions |
| BUG+1 | Extreme | Avoids the “bivalue universal grave” |
| Jellyfish | Extreme | The X-Wing over four rows and columns |
| Finned X-Wing | Extreme | An X-Wing with an extra candidate (the fin) in one corner box |
| Empty Rectangle | Extreme | A box’s candidates for a digit in one row and one column, joined to a strong link |
| X-Chain | Extreme | A longer chain of strong and weak links on one digit |
| XY-Chain | Extreme | A chain of two-candidate cells, the longer cousin of the XY-Wing |
| Alternating Inference Chain | Extreme | A chain of strong and weak links mixing digits, cells and box-line groups |
Almost every newspaper, book and app puzzle can be solved with these. A few of the very hardest need forcing chains or trial and error. When no technique applies, the solver tells you and offers to reveal one cell from the solution so you can keep going.
Tips for learning with the solver
- Try the Hint first. Knowing the technique and where to look is often enough to find the move yourself.
- Read the reason, not just the move. Each explanation says why the move is safe. That is the part that carries over to the next puzzle.
- Note the hardest technique. Solve all rates the puzzle by the hardest step it needed, which shows you the technique to practise next. Our technique guides go through each one with examples.
- Look back over the steps. The step list shows every move in order, and Undo lets you go back and try to find a step on your own.
Want a fresh puzzle instead? Play sudoku at any level, or try the daily puzzle. For more on getting the most from the solver, see How to Use a Sudoku Solver.