How to Play Sudoku Online for Free
November 9, 2026 · by Game Zone Team
Sudoku is the most popular puzzle in the world, and it is also one of the easiest to start. There is one rule, it fits in a single sentence, and you can learn it in two minutes. The puzzle itself, though, can keep you busy for the rest of your life.
This guide explains how to play Sudoku online for free, from the very first grid to the techniques that solve the harder puzzles. No download, no sign-up, no maths degree needed.
The one rule
A Sudoku puzzle is a grid of 9 rows and 9 columns, divided into nine 3 by 3 boxes. Some of the cells already have numbers in them. Your job is to fill in the empty cells with the digits 1 to 9, so that every row, every column and every 3 by 3 box contains each digit exactly once.
That is the whole rule. There is no arithmetic. You never add, subtract or multiply anything. It is a logic puzzle, not a maths puzzle, and the numbers could just as easily be colours or shapes. What matters is that each digit appears once in each row, once in each column and once in each box.
A proper Sudoku has exactly one solution, and it can be reached by logic alone. You should never need to guess. If you find yourself guessing, you have missed a step — go back and look again.
A short history
Sudoku was created by Howard Garns, a retired American architect, and first published in May 1979 in Dell Pencil Puzzles & Word Games magazine, under the name Number Place. The rules were already exactly the ones we use today.
The puzzle reached Japan in the early 1980s, where the publisher Nikoli gave it the name Sudoku in 1984. Sudoku is short for a Japanese phrase meaning roughly “the digits must remain single” — a neat summary of the one rule. Nikoli also set the style of the modern puzzle: the given numbers arranged in a symmetrical pattern, and no more than about 32 of them, so that solving takes real thought.
Sudoku stayed popular in Japan for twenty years before going worldwide. The Times of London printed its first Sudoku on 12 November 2004, and within a year the puzzle was in newspapers all over the world. Today it is played online by millions of people every day, which is why there are so many good free versions to choose from.
How a puzzle works
Every Sudoku starts partly filled. The numbers already in the grid are called givens, or clues. An easy puzzle has more givens — often 35 or more — and a hard puzzle has fewer, sometimes as few as 17. The fewer givens, the more you have to work out for yourself.
Your first job in any puzzle is to look, not to write. Scan the grid. Find a row, column or box that already has eight of its nine digits filled. The missing digit is the only one that can go in the empty cell, and you can write it in with confidence. That is your first solved cell, and it will often unlock the next one.
Then keep going. Each number you place removes possibilities from its row, column and box, which makes the next number easier to find. Easy puzzles can be solved entirely this way, one certain step at a time.
Beginner technique 1: scanning
Scanning is the first technique to learn, and it solves most easy puzzles on its own. Pick a digit, say 5, and look for it in every row, column and box. When you find a box where 5 can only go in one cell — because the other cells in that box are already filled, or because 5 already appears in the same row or column as those cells — write it in.
Work through the digits from 1 to 9, then start again. Each pass finds a few more numbers, and each number you place makes the next pass easier. Slow down and be systematic. Rushing through a Sudoku is how mistakes happen.
Beginner technique 2: pencil marks
Pencil marks are small notes you write in the corner of an empty cell, listing the digits that could still go there. Most online Sudoku games have a pencil-marks mode — usually a button or a keyboard shortcut — that lets you add and remove them easily.
Pencil marks turn guessing into reasoning. When a cell has only one possible digit left in its pencil marks, that digit is the answer. When a digit can only go in one cell within a box, even though that cell has other pencil marks, that digit belongs there. These two ideas — a cell with one candidate, and a digit with one home — solve most medium puzzles.
Do not be shy about using pencil marks. They are not cheating. Every serious Sudoku player uses them, and the best players use them from the very first move.
Beginner technique 3: look for pairs
As you get more confident, start looking for pairs. If two cells in the same row, column or box both have the same two pencil marks — say both can only be 3 or 7 — then those two cells must hold 3 and 7 between them. That means no other cell in that row, column or box can be 3 or 7, and you can remove those digits from their pencil marks. This often leaves another cell with only one candidate, and the puzzle moves forward again.
You do not need to learn every advanced technique to enjoy Sudoku. Scanning, pencil marks and pairs will carry you through easy and medium puzzles, which is where most of the fun is.
Difficulty levels
Most free Sudoku sites offer four or five difficulty levels. Easy puzzles have more givens and can be solved with scanning alone. Medium puzzles need pencil marks. Hard puzzles need pairs and more advanced patterns. Expert or extreme puzzles need techniques with names like X-Wing and Swordfish, and they can take an hour or more.
Start on easy, and stay there until you can finish a puzzle without guessing and without getting stuck. Then try medium. There is no rush to reach the hard levels — an easy Sudoku solved cleanly is more satisfying than a hard one finished by luck.
If you are not sure how much time a puzzle will take, How to Choose the Right Browser Game for a Short Break helps you match a game to the time you have. An easy Sudoku takes about ten minutes. A hard one can take the best part of an hour.
Where to play for free
There are many free Sudoku sites, and most of them are good. A good free Sudoku site has a few things in common. It lets you play without creating an account. It offers several difficulty levels. It has a pencil-marks mode, an undo button, and a hint button for when you are stuck. It checks your entries as you go, or lets you turn that checking off if you prefer to find your own mistakes.
Be careful with sites that cover the grid in adverts, or that ask for payment details before you can play. A free Sudoku needs neither. The Best Free Online Games No Download lists free games that work straight in the browser, with no download and no sign-up.
Sudoku variants
Once you are comfortable with the standard 9 by 9 grid, there are variants worth trying. Mini Sudoku uses a 6 by 6 grid with 2 by 3 boxes, and is a good choice for a quick game or for children. Killer Sudoku adds cages — groups of cells with a target sum — so you do need a little arithmetic after all. There are also larger grids, diagonal Sudoku, and puzzles that use letters or symbols instead of digits. The one rule stays the same in every version: each symbol appears once in each row, column and box.
Common mistakes
The most common mistake is writing a number you are not sure about. If you are not certain, use a pencil mark instead. A wrong number early in a puzzle can make the whole grid impossible, and finding the error takes longer than the puzzle itself.
The second mistake is forgetting to update your pencil marks. When you place a number, remove it from the pencil marks of every other cell in the same row, column and box. Stale pencil marks are the main reason beginners get stuck on medium puzzles.
The third mistake is only looking at rows. Remember that every number has to work in its row, its column and its box at the same time. If a move works in the row but breaks the box, it is the wrong move.
Why Sudoku is so addictive
Sudoku is a puzzle with no luck in it at all. Every puzzle has one solution, and every solution can be found by logic. That is a rare thing in games, and it is why people come back to it. Why Puzzle Games Are So Addictive explains the feeling in detail, but the short version is that Sudoku gives your brain a clear problem and a clear answer, and the pleasure of finding that answer is what keeps you playing.
It is also a calm game. There is no timer unless you want one, no opponent, and no penalty for a wrong move except the time it takes to fix it. That makes it a good game for winding down. If you want something even calmer, Simple Games to Relieve Stress has more ideas along the same lines.
A good way to start
Pick an easy puzzle. Turn on pencil marks. Scan the grid slowly, fill in the certain numbers first, and add pencil marks to the cells you cannot solve yet. When you get stuck, do not guess — look for a cell with one candidate, or a digit with one home. Finish the puzzle, then do another one. After a week of easy puzzles, try a medium. After a month, you will wonder why it ever looked hard.
And if numbers are not your thing, the Best Free Word Games to Play Online offers the same kind of quiet thinking with letters instead of digits.
