Sudoku
Classic sudoku puzzle in 3 difficulties
Online Sudoku: The Classic Logic Puzzle
Place the digits 1–9 without repeats in every row, column and 3×3 box.
Sudoku is a number-based logic puzzle where you fill the board with the digits 1 to 9. The rule is a single sentence: each digit appears exactly once in every row, every column and every 3×3 box. This version runs entirely in your browser, and every puzzle has a unique solution — so you reach the one answer by logic, not guessing. With Easy, Medium and Hard levels you can play from beginner to expert, mark candidate digits with pencil notes, and track your time. Your progress is saved in your browser, so you can close the tab and pick up right where you left off.
Features
3 Difficulties
Easy, Medium and Hard — the number of clues is tuned per level.
Pencil Notes
Mark the possible digits for a cell as small notes.
Mistake Highlight
Conflicts in the same row, column or box show up in red.
Unique Solution
Every puzzle has exactly one answer — no guessing needed.
How to Play
Basic rules
- Place 1–9 once in each row
- Place 1–9 once in each column
- Place 1–9 once in each 3×3 box
- Given (bold) digits can't be changed
Tips
- Start with cells that have only one possibility
- Leave pencil notes where you're unsure
- Focus on one digit and scan the whole board
- If a conflict turns red, undo and try again
Frequently Asked Questions
How do you play sudoku?
The goal is to fill the 9×9 board with the digits 1–9 so that each digit appears exactly once in every row, every column and every 3×3 box. Select a cell and tap the number buttons (or press 1–9 on your keyboard) to place a digit.
What makes the difficulty levels different?
Difficulty depends on how many clues (filled cells) you start with. Easy gives more clues; Hard starts with fewer, which calls for more advanced techniques.
What are pencil notes for?
If you're not sure which digits can go in a cell, turn on Notes and mark them as small candidates. It helps you eliminate possibilities, just like playing on paper.
Does the puzzle have a single solution?
Yes. Each generated puzzle is created with a solution-count check and has exactly one valid solution, so with correct logic you never need to guess.
Is my progress saved?
Yes, your game is stored in your browser. Close the tab and come back, and you'll continue the same puzzle from where you left off. The data never leaves your device.
Is it free? Do I need an account?
It's completely free and needs no account. The game runs entirely in your browser — no installation or sign-in required.