Sudoku Online

Free browser-based Sudoku with unique-solution puzzles, four difficulties, notes and hints — everything runs and saves on your device.

Features

🧩

A backtracking generator builds fresh boards and verifies each has exactly one solution.

🎚️

Choose intro, easy, medium or hard — difficulty scales with how many cells are removed.

✏️

Toggle note mode to jot candidate numbers in a neat 3×3 mini-grid inside any cell.

🚦

Optional real-time checking flags duplicate numbers in any row, column or box in red.

↩️

Step back through every move, redo, or reveal the correct value for a stuck cell.

💾

Your board, timer and difficulty are saved locally so you can refresh and keep playing.

Select intro, easy, medium or hard to generate a brand-new puzzle with a guaranteed unique solution.

Tap a cell, then use the number pad or your keyboard. Toggle notes to record candidates.

Use conflict check, hints and undo as needed. Finish the grid to see your time and best record.

What is this Sudoku tool?

It is a free online Sudoku game that generates classic 9×9 puzzles in your browser, each guaranteed to have exactly one solution.

Is it free to play?

Yes. All four difficulties and every feature are completely free with no account or installation required.

Are the puzzles guaranteed solvable?

Yes. A backtracking algorithm verifies that every generated puzzle has one and only one valid solution.

Will I lose my progress if I refresh?

No. Your current board, timer, mistakes and difficulty are saved in local storage, so you can refresh or reopen and continue.

Does it work on mobile and offline?

Yes. The board scales to fit any screen with large touch targets, and the whole game runs offline in your browser.

How do pencil notes work?

Turn on note mode, then tap numbers to add or remove candidate marks shown as small digits inside the cell.