Sudoku Online

Play Sudoku at the level that suits you

Pick a level above and start. Sudoku Online is free, needs no account, and runs in your browser on a phone, tablet or computer. The board on this page is classic 9×9 Sudoku: fill the grid so that every row, column and 3×3 box contains each digit from 1 to 9 once. If you are new, the guided first puzzle walks through the opening moves of a real Easy puzzle. If you know the game, choose a level and go. The full wording of the rules is on the rules page, and every key, button and setting is on the controls page.

What do the five levels mean?

The levels here are defined by technique, not by how many digits a puzzle starts with. Each level needs the techniques of the one before it, plus new ones.

This is the site’s own grading and not an industry standard, so another site’s “Hard” may feel different. Clue counts barely differ between levels in the stored puzzles, averaging about 24 to 25 on all five, which is why the grading looks at technique. The details and the limits of the method are in how Sudoku difficulty is graded.

What is different about playing here?

• Hints that teach. A hint has three levels: where to look, which technique applies, and the move. It is worked out from the digits you have placed, and it names the technique so you can learn it.
• Every puzzle has exactly one solution. The site stores 1,000 classic puzzles for each level, and a check repeated before each release confirms that every one has a single solution and matches its level. You never need to guess.
• Notes that stay out of the way. Switch on pencil marks, let the game remove them automatically when you place a digit, or fill every cell with Auto-notes in one tap.
• Play that fits real life. The game pauses when you switch apps and saves your board in your browser, so an interruption does not cost you the puzzle.
• Accessible by design. The whole game can be played from the keyboard, the grid is announced to screen readers, and highlights never rely on color alone. A colorblind-safe palette, large digits and a dark theme are in the settings.

The generation guide explains how the puzzles are built and checked, so you can see what “verified” means here.

Which other boards can you play?

Classic Sudoku is the starting point, and ten other boards each change one real rule. The games hub lists all of them. Five that show the range:

• Killer Sudoku replaces most of the givens with cages that must add up to a stated sum.
• Diagonal Sudoku makes both long diagonals hold every digit once.
• Irregular Sudoku swaps the square boxes for jigsaw-shaped regions.
• Sudoku 16×16 scales the grid up to 256 cells and sixteen symbols.
• Daily Sudoku gives every player the same puzzle each UTC day, with a streak in your browser.

Smaller grids, hyper windows, the anti-knight rule and a no-help expert mode are all on the hub too.

How do you get better at Sudoku?

Improvement comes from learning one technique at a time and recognizing it in real puzzles. The site has four sections for that, and each is written to be checked against the game.

• The guides hub has ten tutorials on playing, solving, pencil marks, mistakes and mobile play. The pillar, how to solve Sudoku, is a complete method from singles to unique rectangles with a worked example.
• The techniques hub has a lesson for each of the twelve techniques, with a diagram drawn from a real puzzle and the level at which this site first needs it.
• The history hub covers where Sudoku came from and the mathematics behind it.
• The games hub is where to go when you want a different kind of puzzle.

A short routine for a first session

1. Choose Easy and play one puzzle using only the two singles. Do not use pencil marks yet.
2. If you stall, ask for the second hint level, which names the technique without giving the move, and then find the move yourself.
3. When Easy feels comfortable, try Medium and switch on notes when the singles run out. The pencil marks guide shows how.
4. Read the lesson on pointing pairs, the technique most Medium puzzles use, and look for one in your next game.

How do you use it on a phone?

Tap a cell, then tap a digit on the pad. The Notes button switches to pencil marks, and double-tapping a digit arms it so every cell you tap receives it. Large digits and a left-handed pad layout are in the settings. The mobile tips guide covers these and what to do if the game pauses or a puzzle does not load.

Your questions

Common questions, such as whether progress is saved, how the daily puzzle works and what data the site collects, are answered on the FAQ. Unfamiliar words are in the glossary.