Sudoku: free online puzzles, from Easy to Expert

How to play Sudoku

1. Tap or click an empty cell to select it.
2. Tap a number from 1 to 9 on the number pad, or type it on your keyboard, to fill the cell.
3. Make sure each row, each column and each 3×3 box contains every number from 1 to 9 exactly once.
4. Use Notes to pencil in possible numbers, Undo to take back a move and Hint if you get stuck.
5. Fill all 81 cells correctly to solve the puzzle and record your time.

The rules in one sentence

Place the numbers 1 to 9 so that no number repeats in any row, any column or any of the nine 3×3 boxes. The starting numbers (the clues) cannot be changed. That is all: no maths and no guessing, only logic. Here is a classic starting grid:

Look at the top-left box: it already has 5, 3, 6, 9 and 8. The empty cells in that box must hold 1, 2, 4 and 7, and the rows and columns around them tell you which goes where.

Controls

• Phone and tablet: tap a cell, then tap a number on the pad. Tap the same number again to clear the cell. The small figure under each number shows how many are still missing.
• Keyboard: arrow keys to move, 1–9 to fill, Backspace or 0 to erase, N for notes, Z to undo, H for a hint and P to pause.
• Notes (pencil marks): with Notes on, numbers go into the cell as small candidates. Notes in the same row, column and box are cleared automatically when you place a number.
• Pause: tap the pause button to hide the board and stop the clock.

Difficulty levels

Easy and Medium puzzles are checked by a logic grader to make sure they can be finished with singles alone, so they never require trial and error. Hard and Expert puzzles are chosen because singles are not enough.

Hints that teach you Sudoku

Most Sudoku apps answer "Hint" by quietly filling in a number, so you learn nothing. Here, the coach finds the next step a strong human solver would take and shows it on the board: the row, column or box to look at is shaded, the cells that matter glow gold and the numbers that block other cells are outlined in red. A short explanation names the technique and says why it works. On harder puzzles the coach walks you through a few steps, for example a pointing pair that crosses out candidates, followed by the hidden single it unlocks. Reading the explanation is free; you can reveal the answer itself up to three times per game. The coach also spots wrong numbers and tells you which cell to fix.

The coach knows full houses, naked and hidden singles, pointing, box/line reduction, naked and hidden pairs, naked triples, X-wings and Y-wings, which covers almost every position you will meet on Easy to Expert.

Challenge a friend

Solved a puzzle? Tap Challenge a friend, type your name and send the link. Your friend opens exactly the same puzzle with your time shown at the top as the target, and when they finish they see whether they beat you. The whole puzzle travels inside the link, so there is no account and nothing to install. Send it back for a rematch!

Solving techniques, from basic to advanced

1. Naked single

Look at one empty cell and cross out every number already in its row, column and box. If only one number is left, it must go there. This is how you solve most Easy puzzles.

2. Hidden single

Pick a number, say 7, and a box (or row or column) that does not have it yet. If 7 can fit in only one cell of that box, it goes there, even if that cell has other candidates too.

3. Naked pair

If two cells in the same unit can only be the same two numbers, for example 4 and 9, those numbers belong to those two cells. Remove 4 and 9 from the notes of every other cell in that unit.

4. Pointing

If, inside a box, a number can only go in cells that share one row, then that number cannot appear anywhere else in that row outside the box.

5. X-wing

When a number can go in exactly two cells in each of two rows, and those cells line up in the same two columns, the number must be at two opposite corners of that rectangle. You can remove it from the rest of both columns.

Tips to solve faster

1. Scan by number. Take the number that already appears most often and look for where its missing copies can go.
2. Finish the nearly full units first. A row with seven numbers gives you two easy placements.
3. Use notes on harder puzzles. Writing all candidates in a box makes pairs and pointing patterns easy to spot.
4. Use the highlight. Select a placed number to light up all its copies; empty cells outside the lit rows, columns and boxes are where it can still go.
5. Never guess. Every puzzle here has one logical solution. If you feel you must guess, look again for a hidden single.
6. Take a break. Pause the game, look away and come back. A fresh look often reveals the next move.

A short history of Sudoku

Number puzzles similar to Sudoku appeared in French newspapers in the 1890s, but the modern puzzle was designed by American architect Howard Garns and published by Dell Magazines in 1979 as Number Place. In 1984 the Japanese publisher Nikoli introduced it in Japan as Sūji wa dokushin ni kagiru ("the digits must be single"), soon shortened to Sudoku. New Zealander Wayne Gould brought it to The Times in London in 2004, and within a year it was printed in newspapers all over the world. There are about 6.67 × 10²¹ valid completed Sudoku grids, and a puzzle needs at least 17 clues to have a unique solution.

Frequently asked questions