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Sudoku Solver

Enter your puzzle and solve it instantly, or step through the solution to learn each technique.

How Our Sudoku Solver Works

This solver combines human-readable techniques with a backtracking algorithm to crack any valid Sudoku. It's not a brute-force tool - step-by-step mode walks you through each deduction so you can actually learn the strategies behind the solution.

Solving Techniques Explained

Techniques get applied in order, starting simple and escalating:

Naked Single

Only one candidate left in a cell? That's your digit. The most basic technique, but it cascades constantly.

Hidden Single

A digit can only fit in one cell within a row, column, or box. Even if that cell has other candidates, the digit goes there.

Naked Pair

Two cells in the same unit share the exact same two candidates. Those digits get eliminated from every other cell in the unit.

Pointing Pair

A candidate within a box only appears in one row or column. That lets you eliminate it from the rest of that row/column outside the box.

Box/Line Reduction

Flip side of pointing pair: when a candidate in a row or column lives entirely within one box, eliminate it from the rest of that box.

Hidden Pair

Two digits in a unit only appear in the same two cells. Strip out every other candidate from those cells - only the pair matters.

Multi-Variant Support

Four variants, one solver:

9×9 Classic

Classic 9×9 grid with the standard row, column, and 3×3 box rules.

6×6 Mini

Smaller 6×6 grid with 2×3 boxes. Quick solves, great for learning.

Killer Sudoku

Killer Sudoku with cage constraints and target sums. Define your cages and the solver handles the combinatorial heavy lifting.

Diagonal Sudoku

Diagonal Sudoku with two extra constraints - both main diagonals need digits 1–9.

Tips for Using the Solver

Frequently Asked Questions

What is a Sudoku solver?

It takes a partially filled grid and finds the complete solution. Ours uses human techniques first (naked singles, hidden singles, pairs, etc.) and falls back to backtracking when needed.

Can this solver handle different Sudoku variants?

Four: classic 9×9, mini 6×6, Killer Sudoku (cage constraints), and Diagonal Sudoku (diagonal constraints). Pick the variant tab before you enter your puzzle.

How does the step-by-step solving work?

It applies techniques in difficulty order. Each step highlights the cells involved, names the technique, and explains the reasoning. A solid way to learn strategies you haven't encountered before.

What does Validate do?

Two checks: first, are there any conflicts (duplicate digits in rows, columns, or boxes)? Second, does the puzzle have exactly one solution? Both must pass for Validate to give the green light.

Is there a formula to solve Sudoku?

No single formula, but there's a systematic approach. Start with naked singles and hidden singles, then move to pairs and intersections. The step-by-step solver shows exactly this progression. When techniques run out, backtracking with constraint propagation guarantees a solution.

What is the best strategy for solving Sudoku?

Naked and hidden singles first - always. Scan every row, column, and box for cells with one possible digit. Then hunt for pairs and intersections. Pencil marks help you track what's left. That's the exact progression the solver uses.

What is the trick to solve Sudoku?

Elimination over guessing. Scan for naked singles (cells where only one digit works), then hidden singles (digits that only fit one cell in a unit). Get comfortable with these two and you'll handle most easy-to-medium puzzles without ever needing to guess.

How do you solve a Sudoku puzzle?

Scan for naked singles first - cells with just one valid digit. Then look for hidden singles - digits that only fit one spot in a row, column, or box. Harder puzzles call for naked pairs, pointing pairs, and box-line reduction. The solver demonstrates all of these, step by step.

Explore More Sudoku

Classic Sudoku

Play free 9×9 Sudoku puzzles in five difficulty levels.

Killer Sudoku

Cage constraints with target sums — a harder twist.

Diagonal Sudoku

Diagonal constraints for players who want more.

Sudoku Strategies

From scanning basics to X-Wing and Swordfish - all techniques covered.

How to Play Sudoku

Rules, basic techniques, and tips for your first game.