Sudoku Solver — Step by Step
Enter a puzzle to solve it step by step with detailed explanations.
Example: load a sample puzzle
Solving…
Enter a puzzle to solve it step by step with detailed explanations.
Example: load a sample puzzle
Enter any valid Sudoku puzzle — either as an 81-character string (using digits and
0 or . for empty cells) or by typing a puzzle ID from this
site — and the solver will analyse it and break it down into a sequence of
individual logical steps, from the first digit placed to the last.
The solver works the same way a human player would: it always tries the simplest available technique first, only escalating to more complex reasoning when easier approaches are exhausted. At the simplest end, some cells can be filled immediately because only one digit is possible given what is already in their row, column, or 3×3 box. Moving up the scale, the solver looks for situations where a particular digit can only fit in one cell within a unit, then progressively applies more advanced constraint-based logic that considers interactions between groups of cells or candidates across multiple units. If no purely logical deduction is sufficient, the solver can also make a reasoned guess and backtrack if it leads to a contradiction.
Every step displays the grid as it looks at that moment, with colour-coded highlighting to draw your attention to the relevant cells. A badge indicates the type of reasoning used — placement, elimination, or guess — and the explanation describes exactly why that digit can (or cannot) go in that cell. Use the navigation buttons or the arrow keys to move through the steps at your own pace.
The overall difficulty of a puzzle depends directly on the most advanced technique required to solve it. A puzzle that can be solved from start to finish using only the simplest deductions is rated Beginner. As the required techniques become more sophisticated, the rating climbs through Easy, Medium, Hard, and Expert. The step-by-step solver lets you see exactly which techniques a specific puzzle demands — a practical way to understand why a puzzle felt harder than expected, or to study techniques you have not yet mastered.