How does the solver work?

It uses backtracking — trying valid numbers cell by cell and undoing dead ends — to find a complete solution to any solvable grid you enter, almost instantly.

What do the difficulty levels change?

Difficulty controls how many cells are revealed: easy puzzles start with more clues, hard puzzles with fewer, making them tougher to complete.

How does the solver find the answer?

It uses backtracking: it fills the first empty cell with a valid number, moves on, and if it reaches a dead end it backs up and tries the next option. This systematically explores possibilities until the grid is complete.

What changes between difficulty levels?

Difficulty controls how many cells are revealed as clues. Easy grids start with around forty filled cells, medium with about thirty-two, and hard with roughly twenty-six, so fewer clues mean a harder solve.

Can I enter my own puzzle to solve?

Yes. Clear the board or type over the cells with the puzzle you want solved, then press Solve. If the grid has a valid solution the tool fills it in; if not, it tells you the entries conflict.

Are generated puzzles guaranteed solvable?

Yes. Each puzzle is created by removing cells from a fully solved, valid board, so a solution always exists. Very hard grids may have more than one solution, but they are always completable.

Can I race a friend to solve the same sudoku?

Yes. Open "Play with friends" to start a Sudoku Race room and share the link. Everyone receives the identical seeded puzzle, live progress bars show how full each grid is, and the first player to complete it correctly wins. No download or account is required.

Do all players get the same sudoku puzzle?

They do. The puzzle is generated from a shared seed tied to the room, so every player solves exactly the same grid at the same difficulty. That keeps the race fair — the winner is the fastest accurate solver, not whoever got an easier board.

Sudoku Generator & Solver

Create fresh Sudoku puzzles at three difficulty levels and play them in the grid, or enter an existing puzzle and let the solver complete it instantly. Everything runs locally.

Updated June 2026

Files never leave your browser

How to use Sudoku Generator & Solver

This Sudoku tool does two jobs in one place: it generates fresh puzzles at easy, medium, and hard difficulty for you to play directly in the grid, and it solves any valid puzzle you type in using a fast backtracking algorithm. Generated puzzles start from a complete, valid solution with cells removed according to difficulty, and the solver can complete a partially filled grid or check that a puzzle is solvable. Everything runs in your browser, so you can play offline and your progress never leaves the page.

Click New Easy, Medium, or Hard to generate a puzzle.
Type numbers into the empty cells to play.
Use Clear Entries to reset your own numbers without losing the clues.
Press Solve to complete the grid or check solvability.
Generate a new puzzle any time to start over.

Your data never leaves your device — 100% private processing.

How puzzles are generated

The generator first builds a complete, valid Sudoku solution by filling an empty grid with a randomised backtracking pass, so every game starts from a genuine solved board. It then removes cells one at a time until the target number of clues for your chosen difficulty remains. Because the puzzle is carved from a real solution, it is always solvable. Easy puzzles leave more clues to give you a gentle start, while hard puzzles strip the grid down so you must rely on advanced deduction rather than obvious placements.

Rules and solving strategy

Sudoku has one rule: every row, every column, and every three-by-three box must contain the digits one to nine exactly once. From that single constraint a rich set of strategies follows. Beginners look for cells where only one digit fits, or numbers that can only go in one place within a row, column, or box. Harder puzzles need techniques like pencilling in candidates and spotting pairs or hidden singles. The solver here applies pure backtracking, which is exhaustive rather than human-style, so it can finish any grid even when no simple logical step is available.

Play Sudoku Race multiplayer with friends

Turn solo sudoku into a competitive Sudoku Race. Hit "Play with friends", create a room, and share the code so everyone solves the exact same seeded puzzle at once. Live fill bars show how far each player has progressed, and the first person to complete the grid correctly wins — speed and accuracy both matter because a wrong solution will not finish. The shared seed guarantees identical difficulty for every player, making it a genuinely fair race. It is a free, no-install multiplayer sudoku game you can start in seconds from any browser. Browse every head-to-head game on the multiplayer games hub.

Worked examples

Easy game

Inputs: New Easy

Result: Grid with ~40 clues to play

Solve a puzzle

Inputs: Typed grid · Solve

Result: Completed 9×9 solution

Glossary

Clue: A pre-filled given cell that you cannot change while playing.
Backtracking: A trial-and-undo search that explores possibilities to find a solution.
Box: One of the nine three-by-three regions that must hold the digits 1–9.
Candidate: A digit that could legally go in a given empty cell.

Frequently Asked Questions

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Why use Sudoku Generator & Solver?

Generates playable puzzles at three difficulty levels on demand
Solves any valid grid instantly with a backtracking algorithm
Distinguishes given clues from your entries so the board stays clear
Runs entirely in the browser — play offline with nothing uploaded

Common use cases

Generate a quick puzzle to play during a break
Print a fresh grid at a chosen difficulty for offline solving
Solve a puzzle from a newspaper or book when you get stuck
Check that a Sudoku you created has a valid solution
Practise solving techniques at progressively harder levels

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