Sudoku

How to Play Sudoku

Sudoku is a logic puzzle on a 9x9 grid split into nine 3x3 boxes. Some cells arrive pre-filled as givens; your job is to complete the grid so every row, every column, and every 3x3 box contains each digit from 1 to 9 exactly once. No math is involved - only pure deduction, and every puzzle generated here has exactly one solution.

Click a cell (or move with the arrow keys) and type a digit or tap the number pad. The board checks your work live: a wrong entry turns red and counts as a mistake, and three mistakes end the run - though you can keep playing casually. Toggle pencil mode to jot small candidate digits in a cell while you reason, and watch the highlighting: selecting a cell lights up its row, column, box, and every matching digit on the board. Beat the clock across four difficulties, from a gentle Easy to a brutal Expert with barely two dozen clues.

Strategy Tips

• Start with the most crowded digits - pick the number that already appears six or seven times on the board and chase its remaining placements. Rows and boxes it can't enter narrow the options fast.
• Scan boxes in bands of three - if a digit sits in two of three horizontally adjacent boxes, its position in the third box is confined to one row. This "cross-hatching" solves most Easy and Medium cells without any notes.
• Hunt naked singles after every entry - each digit you place changes what its 20 peer cells can hold. Re-check those cells immediately; chains of forced entries often cascade from a single placement.
• Use pencil marks for pairs, not everything - noting every candidate buries the signal. Mark cells that are down to two or three options; when two cells in a unit share the exact same pair, that pair is eliminated everywhere else in the unit.
• On Expert, look for pointing candidates - when all of a box's candidates for a digit fall in one row or column, that digit is banned from the rest of that line. It's the key that unlocks most low-clue puzzles.

Playing Sudoku on PlayVersusAI

Standard 9x9 Sudoku: fill the grid so every row, every column and every 3x3 box contains the digits one to nine exactly once. Four difficulty levels, pencil marks for candidates, optional error checking, and a timer if you want to race yourself.

Puzzles are generated fresh each time rather than pulled from a fixed library, so you will not see the same grid twice. Every puzzle is verified to have exactly one solution, and — more importantly — to be solvable by logic alone at the difficulty you chose. You will never be forced to guess, and if you find yourself wanting to, there is a deduction available that you have not spotted yet.

What's on This Page

• High-score table — fastest times are ranked on the global leaderboard when you are signed in.
• No account required — the full game is playable as a guest, on desktop, tablet or phone.

The four levels differ in which solving techniques are required. Easy needs only naked singles — squares with one possible value. Medium adds hidden singles. Hard requires pairs and pointing candidates. Expert demands the harder chain techniques, and is genuinely difficult rather than just sparse.

Mistakes That Lose Games

• Guessing when stuck. Every puzzle here is solvable by deduction. A guess that turns out wrong wastes far more time than the minute you would have spent finding the logic.
• Not using pencil marks on harder grids. Expert puzzles are effectively impossible to hold in your head, and candidate notation is a tool rather than a crutch.
• Only scanning rows and columns. Boxes are the third constraint and are where hidden singles usually turn up.
• Filling in the easy digits and stopping. Once the obvious placements run out, switch technique rather than re-scanning the same way and hoping.

Sudoku Questions

For the complete rules, the deeper strategy and the history of the game, read the full Sudoku guide, or browse guides for all 20 games.