---
title: "Sudoku Solver - Complete Any 9 x 9 Puzzle"
description: "Solve any standard 9 x 9 Sudoku puzzle online. Enter the clues, catch conflicts instantly, and copy the completed grid without uploads or sign-up."
url: https://candoya.com/tools/sudoku-solver/
locale: en
type: browser-tool
---

# Free Sudoku Solver

Category: [Games & Fun](https://candoya.com/tools/games/)

## What does a Sudoku solver do?

A Sudoku solver completes a standard 9 x 9 number puzzle so every row, column, and 3 x 3 box contains the digits 1 through 9 exactly once. Enter your starting clues and this browser tool checks them for conflicts, finds a valid solution, and marks solved cells separately from your original numbers.

The solver works locally in your browser, so the puzzle is not uploaded and no account is needed. It uses constraint checking plus backtracking: it tries the cell with the fewest legal candidates first, which avoids much of the blind searching done by a simple left-to-right solver.

Duplicate digits are highlighted before solving. A puzzle can also be valid so far but impossible to finish; in that case, the grid stays unchanged and the status explains that no complete solution exists.

## How to use it

1. **Enter the clues** - Select each matching square and type a digit from 1 to 9, or tap a digit on the number pad. Leave unknown cells blank.
2. **Fix highlighted conflicts** - If a digit repeats in a row, column, or 3 x 3 box, the conflicting cells turn red. Correct them before solving.
3. **Solve the puzzle** - Choose Solve puzzle. Your clues stay dark while the digits found by the solver use the accent color.
4. **Copy or start again** - Copy the completed grid as nine text rows, or reset the board and enter another puzzle.

## Who it's for

- **Stuck puzzle solvers** who want to check the finished grid after making their own deductions.
- **Puzzle setters** testing whether a set of clues can produce a complete valid grid.
- **Teachers and learners** comparing starting clues with solved cells using the two number styles.
- **Mobile players** entering a printed puzzle with a large on-screen number pad instead of a keyboard.

## Expert note

A grid with no duplicate clues is not necessarily solvable. This solver also checks the deeper case where every clue is locally legal but the remaining candidates eventually reach a dead end.

## Frequently asked questions

### Is this Sudoku solver free?

Yes. You can enter and solve as many standard 9 x 9 puzzles as you like without payment, registration, or a download. The example, conflict checker, full solver, mobile keypad, and copy function are all available for free.

### Is my Sudoku puzzle uploaded?

No. The puzzle is checked and solved by JavaScript running in your browser. Your clues are not sent to a solving server, stored in an account, or included in the copied result unless you choose to paste that result somewhere else.

### What kinds of Sudoku can this tool solve?

It solves classic 9 x 9 Sudoku puzzles that use digits 1 through 9 and the standard row, column, and 3 x 3 box rules. It does not support variants with cages, diagonals, irregular regions, extra symbols, or grids of another size.

### How does the Sudoku solver find the answer?

The solver calculates the legal candidates for each blank cell, selects the blank with the fewest options, and tries those values in turn. If a choice creates a dead end, it backtracks and tries the next candidate until it finds a complete valid grid or proves none exists.

### Why are some Sudoku cells highlighted red?

Red cells contain a repeated digit within the same row, column, or 3 x 3 box. Every cell involved in that conflict is highlighted, not just the most recently edited one. Change or erase one of the duplicates before pressing Solve puzzle.

### Can a Sudoku have more than one solution?

Yes. A loosely constrained grid can allow several valid completions. A properly published Sudoku is normally designed to have exactly one solution. This tool finds a valid completion; it does not certify that the completion is unique.

### Can I use the Sudoku solver on a phone?

Yes. Tap a cell and use the number pad below the grid, including the erase key. On a hardware keyboard you can type digits, use the arrow keys to move between cells, and press Backspace or Delete to clear the selected cell.

## Related tools

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- [Maze Generator](https://candoya.com/tools/maze-generator/)
- [Anagram Game](https://candoya.com/tools/anagram-game/)
- [Reaction Time Test](https://candoya.com/tools/reaction-time-test/)
- [Typing Speed Test](https://candoya.com/tools/typing-speed-test/)

---

*Markdown edition of <https://candoya.com/tools/sudoku-solver/>, published for AI agents and other automated readers. Index of key pages: <https://candoya.com/llms.txt>.*