Solve a puzzle
Enter the puzzle you are stuck on — type the
given digits straight into the grid, or paste an 81-character line of digits
(use 0 or . for a blank). Then press Solve.
The tool first checks that your givens are legal, then works the grid the way
a person would, and shows you exactly how it reached each answer. Use
Load example to try it instantly, or Clear to start over.
This solver runs on JavaScript, which appears to be turned off. You can still play the full Sudoku game in your browser — it generates and solves every puzzle on device and works offline.
How it was solved
How the solver works
Everything happens on your device. Nothing you type is uploaded, there is no account, and there is no tracking — the puzzle is solved by a small program running inside this page. When you press Solve, it first validates your givens: if the same digit appears twice in any row, column, or 3×3 box, it stops and tells you where, rather than pretending to solve an impossible grid.
If the givens are legal, it solves the way a person does: it keeps a list of the candidate digits still possible in every empty cell and repeatedly applies named logical techniques to eliminate candidates and place digits. It applies naked singles (a cell with only one candidate left), hidden singles (a digit that fits only one cell in a row, column, or box), locked candidates (the pointing and claiming eliminations between a box and a line), and naked and hidden pairs. When straightforward logic runs out, it falls back to a guaranteed backtracking search to finish — and it says so honestly in the log rather than dressing up a guess as a deduction.
It also tells you when a puzzle has no solution at all, or more than one solution (a proper Sudoku has exactly one). An empty grid, for instance, has billions of solutions, so the tool reports it as non-unique rather than picking one arbitrarily.
Read the log to learn the techniques
The step-by-step log is the point of this tool. Each line names the technique and explains the reasoning — “Naked single: R4C7 must be 8, the only digit left for that cell”, or “Hidden single: 3 goes in R1C2, the only cell in box 1 that can hold a 3”. Reading along is one of the fastest ways to internalise the patterns and start spotting them yourself. The named techniques here are the same ones the guides walk through in depth.
More Sudoku
Want to play rather than solve? The full game gives you an endless supply of puzzles at every difficulty, with pencil marks, hints, and offline play. If you would rather learn the ideas behind the solver, the guides explain the rules and every named technique step by step, and the studio blog explains how we generate and grade the puzzles in the first place.
Read more: how we generate and grade Sudoku puzzles · Daily Sudoku
Learn the techniques: sudoku glossary · all guides