Sudoku Solver

How to use

1. 1Click any cell in the 9x9 grid, then type a digit from 1 to 9. Use 0, Delete, Backspace, or Space to clear the cell. Arrow keys move the selection.
2. 2Or load a starting position: click Easy, Medium, Hard, or Expert under Generate puzzle to get a fresh unique puzzle, pick a sample from the list, or paste an 81-character puzzle string into the import box and click Load puzzle.
3. 3Watch for red cells. Any conflict with the row, column, or 3x3 box rule is highlighted in real time so you can fix typos before you solve.
4. 4Click Solve. The tool fills every empty cell and tells you whether the solution is unique. Cells you typed stay in their colors; new cells appear in green.
5. 5Use Clear entries to drop your own numbers and the solver fill while keeping the original givens. Use Reset grid to empty the board entirely.
6. 6Click Copy line to copy the current grid as an 81-character string, or Copy grid to copy a printable ASCII block. Both include your entries and the solver result.

About this tool

Sudoku Solver fills any valid 9x9 Sudoku puzzle in your browser. Type the clues or paste an 81-character puzzle string, click Solve, and the tool returns a completed grid with the original givens in white, your own entries in blue, and the cells the solver filled in green. Conflict checking runs in real time: any cell that breaks the row, column, or 3x3 box rule is highlighted in red the moment you type it, so you spot a mistyped clue before you waste minutes on a dead-end search. Under the hood the solver uses constraint propagation followed by backtracking with the minimum-remaining-value heuristic: it computes the candidate digits for every empty cell, picks the cell with the fewest candidates, and recurses through each option. The search keeps going past the first solution so it can tell you whether the puzzle is well-formed (exactly one solution) or ambiguous (two or more). The tool also generates fresh puzzles at Easy, Medium, Hard, and Expert levels by building a uniformly random valid grid and removing givens one at a time while preserving uniqueness, so every generated puzzle has exactly one answer. Four sample puzzles cover the difficulty band from newspaper-easy to expert torture, and the import box accepts any common 81-character format (digits 1 to 9 for clues, plus 0, dot, dash, underscore, or space for blanks). Export the current grid as a compact one-line string for copying into another solver or a printable ASCII block for sharing on paper. Useful for checking a finished puzzle, getting unstuck on a hard one, generating fresh puzzles for a classroom or commute, and verifying that a hand-built puzzle has the single solution a real Sudoku is supposed to have. Everything runs in your browser; nothing you type is uploaded.

Free to use. Works in your browser. No signup, no login.