Sudoku Solver

Type the numbers of your sudoku into the grid (or paste the 81 characters) and solve it instantly. If you want to learn, tap “Explain” and follow the reasoning step by step, with the name of each technique.

Board as text (81 characters)

Type the numbers with the keyboard or tap a cell (on a phone the numeric keypad opens). You can also paste the 81 characters with Ctrl+V over the grid or in the text box. With “Explain” the steps are shown one by one: the cells of the step are highlighted and the eliminations in another color.

Techniques the solver uses

Technique	Level	What it does
Naked single	Easy	A cell has only one possible number.
Hidden single	Easy	A number fits in only one cell of its row, column or box.
Naked pair	Medium	Two cells in the same unit share the same two candidates: those numbers are removed from the other cells.
Hidden pair	Medium	Two numbers fit only in the same two cells of a unit: those cells cannot hold any other candidates.
Pointing pair	Medium	In a box, a number fits only in one row or column: it is eliminated from the rest of that line.
Box/line reduction	Medium	In a row or column, a number fits only inside one box: it is eliminated from the rest of the box.
Naked triple	Hard	Three cells in a unit share only three numbers between them: those are eliminated from the other cells.
Hidden triple	Hard	Three numbers fit only in the same three cells of a unit: those cells lose their other candidates.
X-Wing	Hard	A number appears in only two columns in two different rows: it is eliminated from the rest of those columns (and vice versa).
Swordfish	Expert	Like the X-Wing, but with three rows and three columns.
Y-Wing	Expert	A cell with candidates A and B sees one with A and C and another with B and C: C is eliminated from whatever both wings see.
XYZ-Wing	Expert	A variant of the Y-Wing with a three-candidate pivot: the common number is eliminated from everything all three cells see.

How to solve a sudoku with this tool

Enter the numbers your sudoku already has into the grid, or paste the 81 characters into the text box (dots or zeros for the blanks).
Tap “Solve” to see the full solution; the numbers the solver adds appear in a different color.
If the board is invalid, has no solution or has several, it tells you and marks the repeated numbers.
Tap “Explain” to walk through the solution step by step: each step names the technique used, the cells involved and what is placed or eliminated.

How the solver thinks

The solver does not just try numbers until everything fits: it first solves the way a person would, always applying the simplest technique that works. That makes it possible to explain every step and also to work out the board's level: the level of the hardest technique needed (Easy, Medium, Hard, Expert), or Extreme if logic runs out and hypotheses are required.

The technique table below summarizes the ones it uses, from the simplest to the most advanced. Naked and hidden singles are enough for easy boards; pairs, triples and intersections show up in medium and hard ones; X-Wing, Swordfish, Y-Wing and XYZ-Wing, in expert ones.

Everything happens in your browser: the board you enter is not sent to any server or saved.

Things to keep in mind

A sudoku needs at least 17 numbers to have a unique solution; with fewer, the solver will not solve it.
If the board has several solutions, only the first one is shown and it cannot be explained.
The explanations use the techniques in the table; when they run out, the board requires trying hypotheses and the explanation ends there.

Frequently asked questions

How do I enter a sudoku from a photo or from paper?

Type it into the grid by hand, cell by cell, or build a string of 81 characters with dots or zeros for the blanks and paste it into the text box.

What happens if my sudoku has more than one solution?

It tells you and shows the first solution it finds. This usually means a number was missed when you entered it.

What does the Explain button do?

It shows the solution step by step, with the name of the technique for each step, the cells that form it and which number is placed or eliminated.

Why does it say the level is Extreme?

Because the solver's techniques run out before the board is finished, and a hypothesis has to be tried and followed through to a contradiction.

Is my board saved or sent anywhere?

No. Everything is calculated in your browser, and nothing is saved or sent.

Does it solve variants such as Killer or Samurai?

No, it solves the classic 9×9 sudoku.