Fun
Sudoku
Fill the grid so every row, every column and every 3×3 box contains the digits 1 to 9 exactly once.
Play and explore in your browser. No account needed.
Frequently asked questions
What are the rules of Sudoku?
The board is a 9×9 grid split into nine 3×3 boxes, with some squares already filled in. You must fill every empty square with a digit from 1 to 9 so that no digit repeats in any row, any column or any 3×3 box. No arithmetic is involved — the digits could just as well be letters or colors. A proper puzzle has exactly one valid solution, reachable by logic alone.
How are the difficulty levels different?
Every puzzle is generated with a single solution and then graded by which techniques it needs. Easy and Medium puzzles can always be solved using only singles — a square with one possible digit left, or a digit with only one possible place in a row, column or box. Easy leaves about 40 clues, Medium about 32. Hard removes as many clues as possible, typically leaving 22 to 27, and is chosen so that singles alone cannot finish it — expect to need pairs and pointing candidates, and occasionally something harder.
How do pencil notes work?
Turn on Notes with the button or the N key, and the digits you enter appear as small candidates in the square instead of an answer. Tap the same digit again to remove it. When you later place a real digit, that digit is automatically cleared from the notes of every square in the same row, column and box, which is the bookkeeping most players do by hand anyway.
What do the red numbers mean?
A red digit breaks a rule: the same digit already appears in its row, column or box. This check only compares the digits on the board, so it never reveals the solution. If you want stricter feedback, turn on Show mistakes, which also marks any digit that does not match the puzzle’s solution even when it causes no visible conflict yet.
Is my game saved, and are best times recorded?
Yes, both are stored in your browser’s localStorage on this device only — there is no account and nothing is uploaded. Refreshing or closing the page resumes the same puzzle with its notes and timer. The timer pauses while the tab is hidden, and a best time for each difficulty is recorded only for puzzles finished without hints.
About this tool
This is a clean, free Sudoku that runs entirely in your browser, with no download, no account and no clutter around the grid. Each new puzzle is generated on your device: a complete valid grid is built first, then clues are removed one at a time, and after every removal a solver confirms the puzzle still has exactly one solution. That guarantee matters — a puzzle with two solutions forces guessing, and guessing is not what Sudoku is about.
Difficulty is graded by technique rather than just by counting clues. For Easy and Medium, a clue is only removed if the puzzle can still be finished using naked and hidden singles, the two techniques every player learns first. Hard puzzles go further: the generator strips clues down to a minimal set and picks a grid that singles alone cannot finish, so you will need candidate notes and patterns such as naked pairs, pointing pairs and box-line reduction — and on the toughest grids, more advanced chains. Clue counts on Hard typically land between 22 and 27.
The controls are built for both touch and keyboard. On a phone, tap a square and then a number on the pad; the count under each digit shows how many are still to be placed. On a computer, use the arrow keys to move, 1–9 to enter, Backspace to erase, N to toggle notes and Ctrl+Z to undo. Selecting a square highlights its row, column and box, along with every other square holding the same digit, which makes scanning much faster.
A few solving tips: start with the digit that already appears most often, since it has the fewest places left; scan each 3×3 box for a digit that can only fit one square; and once the obvious singles run out, pencil in candidates for a whole box or row before looking for pairs. If you get stuck, a hint fills in the selected square if it is empty or wrong — otherwise the empty square with the fewest remaining candidates, which is usually the next logical move.
Updated · Novpix LLC