Sudoku is the world's most popular logic puzzle — fill a 9x9 grid so that every row, every column and every 3x3 box contains the digits 1 to 9 exactly once. This free online Sudoku game plays in your browser with no download or sign-up, and it is pure deduction: no arithmetic and no guessing required.
Every genuine Sudoku has one and only one solution reachable by logic alone. With multiple difficulty levels here, you can warm up on gentle grids or test yourself on puzzles that demand advanced techniques.
The idea behind Sudoku goes back to the 18th-century Swiss mathematician Leonhard Euler and his work on Latin squares, but the modern puzzle was designed in 1979 by Howard Garns, an American architect, and published under the name 'Number Place.' It was in Japan that it found its audience and its name — sudoku is short for a phrase meaning roughly 'the digits must be single.'
The puzzle became a global phenomenon in 2004 and 2005, after Wayne Gould created a program to generate grids and newspapers around the world began printing a daily Sudoku. Within months it was a fixture on commuter trains and coffee tables everywhere — a rare puzzle craze that never really faded.
The grid is divided into nine rows, nine columns and nine 3x3 boxes, and it starts partly filled with 'given' numbers. Your task is to fill every empty cell so that each row, each column and each 3x3 box contains all of the digits from 1 to 9 with no repeats. That single constraint — no digit twice in any row, column or box — is the entire rulebook.
There is no counting or arithmetic involved; it is a puzzle of elimination. Every empty cell has exactly one correct digit that can be worked out by ruling out everything its row, column and box already contain.
Click a cell to select it, then type or tap a number from 1 to 9 to fill it; clear a cell to erase. Use pencil-mark notes to jot candidate digits into a cell while you narrow them down. The difficulty setting controls how many numbers are given at the start.
Good Sudoku solving is a ladder of techniques, from simple scanning to elegant chains. Work up this ladder and even hard grids fall to pure logic.
Start with naked and hidden singles. First find cells with only one possible digit (a 'naked single'), and units where a digit can go in only one cell (a 'hidden single'). Scanning for these clears the easy part of every puzzle and often unlocks the harder steps.
Pencil in candidates for every empty cell. Once the obvious placements run out, mark the possible digits in each empty cell. Almost every intermediate technique works by spotting patterns in these candidate marks, so keeping them accurate is the foundation of solving harder grids.
Use naked and hidden pairs to eliminate. If two cells in the same row, column or box can hold only the same two digits, those digits are locked to that pair and can be removed as candidates everywhere else in that unit. Pairs and triples are the workhorses of medium and hard puzzles.
Try pointing pairs and box-line reduction. When a digit's only possible cells within a box all lie in one row or column, that digit can be eliminated from the rest of that row or column outside the box — and the reverse also applies. This interaction between boxes and lines cracks many tough spots.
Learn one advanced pattern: the X-Wing. For the hardest grids, the X-Wing spots a digit that appears as candidates in exactly two cells on each of two rows, lined up in the same two columns — letting you eliminate that digit elsewhere in those columns. It is the gateway to expert technique.
Never guess — always deduce. A proper Sudoku is solvable by logic alone, so if you are tempted to guess, there is a deduction you have missed. Slow down, recheck your candidates and look for the technique rather than gambling and risking a spoiled grid.
Build the habit of scanning for singles, then pairs, then box-line interactions before you reach for advanced patterns; on the hardest level, patient candidate-tracking and techniques like the X-Wing will always beat guessing.
How do you solve a Sudoku?
Fill the grid so that every row, column and 3x3 box contains 1 to 9 with no repeats. You do it by elimination: find cells with only one possible digit, mark candidates, and apply techniques such as pairs and pointing pairs to remove possibilities until the grid is complete.
Is every Sudoku solvable without guessing?
Yes — a well-formed Sudoku has exactly one solution reachable by pure logic. If you feel you must guess, it means there is a deduction available that you have not spotted yet.
What is the best way to start a puzzle?
Scan for singles first: cells with only one candidate, and units where a digit fits in only one place. Clear all of those, then pencil in candidates for the remaining cells before moving on to more advanced techniques.
Is this Sudoku game free?
Yes — play unlimited puzzles free in your browser across several difficulty levels, with no download or sign-up.
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