How to play Sudoku
A complete guide to the rules, the controls of this game and the techniques that solve it.
In one sentence: fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1 to 9 exactly once. Start a puzzle →
The rules of Sudoku
A Sudoku grid has 81 cells, arranged in nine rows, nine columns and nine 3×3 boxes. Some cells already hold numbers - these are the givens and never change. Your job is to fill the rest so that three conditions hold at the same time:
- each row contains the digits 1–9 without repetition;
- each column contains the digits 1–9 without repetition;
- each 3×3 box contains the digits 1–9 without repetition.
No arithmetic is involved - the digits are just nine different symbols. Every puzzle in this game is generated with exactly one valid solution, so you never have to guess: each step can be deduced from the numbers already on the board.
Playing this game
On a phone or tablet
- Tap an empty cell. A small keypad with the digits 1–9 opens right next to it.
- Tap a digit to place it. Tap Notes inside the keypad first if you want to pencil in candidates instead, and Erase to clear the cell.
- Tapping anywhere outside the keypad closes it; the next tap selects a new cell.
On a computer
- Click a cell, then click a digit in the number pad below the board - or simply press 1–9.
- Backspace or 0 clears a cell, the arrow keys move the selection, N toggles notes and U undoes the last move.
Difficulty levels, points and mistakes
Three levels are available, differing in how many givens a puzzle starts with and how much deduction is required:
- Easy - around 36 givens, solvable by simple scanning. Worth 1 point, and you may make up to 2 mistakes; the third ends the puzzle.
- Medium - around 30 givens, needs notes and pairs. Worth 2 points, with a limit of 2 mistakes.
- Hard - around 26 givens, demanding careful elimination. Worth 3 points, and a single mistake ends the puzzle.
Your total points and the number of solved puzzles are shown at the top of the game and stored in your browser, so they survive a reload. Hints are unlimited and never cost points: a hint reveals the correct digit for the selected cell.
Techniques that solve puzzles
1. Scanning (cross-hatching)
Pick a digit, say 5, and look at a 3×3 box that does not contain it. Cross out every row and column in that box that already has a 5 elsewhere. If only one cell survives, that cell must be the 5. This single technique solves most easy puzzles.
2. Naked singles
Look at one empty cell and list the digits that its row, column and box do not already contain. If exactly one digit remains, it belongs there. Using the notes mode makes these obvious: a cell with a single pencil mark is a naked single.
3. Hidden singles
Within one row, column or box, check where a given digit can still go. If there is only one possible cell - even if that cell has several candidates of its own - the digit goes there. Hidden singles are the backbone of medium puzzles.
4. Naked pairs and triples
If two cells in the same unit both have exactly the same two candidates, those two digits are locked into those two cells. They can be removed from every other cell in that unit, which often unlocks a hidden single. The same logic extends to three cells sharing three candidates.
5. Pointing pairs (box-line reduction)
If, inside one box, a candidate digit appears only in cells that share a row, then that digit must be in that row inside the box - so it can be eliminated from the rest of the row outside the box. Mirror the same reasoning for columns. This is usually what breaks open a hard puzzle.
Tips for playing faster
- Start with the digit that already appears most often on the board - it constrains the grid the most.
- Fill notes for a whole box at once rather than jumping across the grid; your eye keeps the context.
- After placing a digit, immediately check the row, column and box it completes. This game removes that digit from the notes of every affected cell automatically.
- On hard puzzles, never guess. One mistake ends the puzzle, and a wrong branch is far slower than elimination.
- If you are stuck, use a hint rather than a guess - it costs no points and keeps the board consistent.
Frequently asked questions
Is this Sudoku game free?
Yes. It is free to play, needs no account and no installation. The game is funded by advertising, described in the Privacy Policy.
Does every puzzle have exactly one solution?
Yes. Each puzzle is generated in your browser and verified to have a single solution, so it can always be solved by logic alone.
Is my progress saved?
Yes. The current puzzle, your notes, the timer, your points and your theme are stored in your browser's local storage. Closing the tab or reloading the page keeps everything. Clearing your browser data removes it.
Can I play offline?
Once the page is loaded, puzzles are generated locally, so the game keeps working without a connection. Reopening it after a full close still requires loading the page once.
What happens when I run out of mistakes?
The puzzle ends and awards no points. You can start a new one immediately - there is no waiting time and no limit on how many puzzles you play.
How many points can I earn?
One point for an easy puzzle, two for a medium one and three for a hard one. The total is kept on your device only, so it is a personal record rather than a global ranking.