Play Sudoku online, from Easy to Evil

Play sudoku free in your browser, with five difficulty levels that mean the same thing every time: each grid has exactly one solution and is rated by the techniques it needs. Notes, Check and hints that name the technique are built in. No app, no sign-up, no interstitial before you play; it works offline and with the keyboard alone.

How to play sudoku

1. The grid has 81 cells in nine rows, nine columns and nine 3×3 boxes. Some cells start filled; these givens cannot be changed.
2. Fill every empty cell with a digit from 1 to 9 so that each row, each column and each box holds every digit exactly once.
3. Select a cell by tapping, clicking or using the arrow keys, then type a digit or use the digit pad. The pad shows how many of each digit are still missing.
4. Turn on Notes (or press N) to pencil in candidates. Placing a digit removes that digit from the notes in its row, column and box.
5. Every puzzle has exactly one solution, found by logic. You never need to guess below Evil.
6. The puzzle is solved when the whole grid matches the solution; the timer stops and your time is saved.

Sudoku strategy: from singles to X-wings

Think of sudoku as a ladder of techniques. Each level adds one rung, and the hint names the rung you need next.

Start with singles

A naked single is a cell where only one digit is left once you rule out everything in its row, column and box. A hidden single is a digit that has only one possible cell in a row, column or box, even if that cell could hold other digits. Scan by digit: pick a 1, look at every box that lacks a 1 and ask where it can go. Easy grids need only naked singles; Medium adds hidden singles.

Use notes once singles run out

When scanning stops finding cells, fill in candidates. Fill notes writes them all at once, and the setting "Start with all notes filled in" does it at the start of every game. From here you are looking for patterns in the notes rather than in the givens.

Pointing pairs and box-line reduction

If a digit’s candidates inside one box all sit in a single row or column, that digit cannot appear elsewhere in that row or column: a pointing pair or triple. The mirror image is box-line reduction: if a digit’s candidates in a row fall inside one box, remove it from the rest of that box.

Naked and hidden pairs

Two cells in a unit with the same two candidates, say 4 and 7, must take those digits between them, so 4 and 7 can be removed from every other cell of that unit. A hidden pair works the other way: if 4 and 7 appear in only two cells of a unit, those cells can lose every other candidate. Triples follow the same logic with three cells. These are the Hard techniques.

X-wing, Y-wing and swordfish

An X-wing appears when a digit has exactly two places in each of two rows and those places share the same two columns; the digit then comes out of the rest of both columns. A swordfish does the same with three rows and three columns. A Y-wing uses three two-candidate cells: a pivot XY that sees wings XZ and YZ, so any cell seeing both wings cannot be Z. Expert grids need these.

Chains for Evil grids

Evil grids need a forcing chain: take a cell with two candidates, assume one, follow the singles, and if that leads to a contradiction the other candidate is right.

What the sudoku difficulty levels mean

A level here is not a guess from the number of clues. Every grid is generated on your device, checked for a unique solution and then solved by a human-style solver that records the hardest technique it needed. Only grids that match the level and fall inside its clue range are used.

• Easy: 36 to 45 clues, naked singles only.
• Medium: 30 to 35 clues, adds hidden singles and pointing pairs and triples.
• Hard: 26 to 30 clues, adds naked and hidden pairs and triples and box-line reduction.
• Expert: 24 to 27 clues, adds X-wing, Y-wing and swordfish.
• Evil: 22 to 25 clues, needs a forcing chain and, rarely, trial and error.
• Kids: 4×4 and 6×6 grids that need singles only, with digits or shapes.

A short history of sudoku

Grids where every symbol appears once in each row and column are Latin squares, studied by the mathematician Leonhard Euler in the 18th century. The puzzle we know, with the extra rule for 3×3 boxes, first appeared in American puzzle magazines in the late 1970s under the name Number Place, and is generally credited to the puzzle constructor Howard Garns.

The Japanese publisher Nikoli introduced it in Japan in the 1980s and gave it the name sudoku, short for a phrase meaning that each digit must appear only once. The puzzle spread worldwide after British newspapers began printing it in 2004, and by 2005 it was in papers around the world.

Mathematicians have since counted about 6.67 × 10²¹ valid completed 9×9 grids, and a computer search published in 2012 showed that a puzzle with a unique solution needs at least 17 clues.

Daily, stats and printables

The daily sudoku is the same grid for everyone each day, Hard by default, with a setting to pick any level, a streak counter and an archive of the last 30 days. Printable sheets turn any level into a PDF, and the solver checks or steps through a grid from a newspaper or book.

The timer starts on your first move and pauses when you switch tabs. each level stats stay in your browser: played, won, win rate, best and average time. Undo and redo cover the whole game. The first two hints per puzzle are free; later hints may offer a short ad or a 30-second wait. A puzzle code such as A7K3Q (?p= in the address) replays the same grid, and the win panel gives a result to share.

Settings cover highlight helpers, conflict highlighting, the mistakes counter and auto-notes.

Plays anywhere, no app, no account

The sudoku grid resizes to fit a phone with the digit pad underneath, and every cell can be reached and filled from the keyboard. Tidy Puzzles runs entirely in your browser: there is no app to install, no account to create and no interstitial before you can play. After the first visit the game also works offline, because each puzzle is generated on your device from a seed. Every board can be played with the keyboard alone, on a phone or a desktop, and your stats and unfinished puzzles stay in this browser rather than on a server.