Number & arithmetic

Sudoku — rules and where to play

SUDOKU · Number Place / Su Doku / Nanpure

Fill every row, column and 3×3 box with 1–9 without repeats. For most players it is the front door to logic puzzles, and the most varied family in the atlas.

Origin: 1979 · United States
Difficulty: ★★★★★ 1–5 / 5
Time: 5–90 min
Grid: 4×4 – 9×9 (16×16 rare)
Sites: 40

Rules

Each row, column and 3×3 box contains 1–9 exactly once.
The given digits are part of the unique solution and cannot change.
Standard Sudoku needs no arithmetic at all — it is pure elimination.

How to start

Sweep for naked singles first

If a cell sees eight different digits, the ninth is the answer.

Then hunt hidden singles

When a digit has only one legal cell in a row, column or box, place it.

Pencil marks in moderation

Two or three candidates per cell is plenty early on; full notation just adds noise.

Change box when you stall

Well-formed Sudoku is meant to be fully deductive; if you are guessing, try another box or a lighter technique first.

Where players get stuck

Substituting trial-and-error for reasoning — you never build instincts that way.
Using hints as an answer key; a good hint explains why that cell must be 7.

Play Sudoku

40 sites

Conceptis PuzzlesFreemium

Long-standing picture and logic publisher: Pic-a-Pix, Slitherlink, Hashi, Kakuro.

Open → Sudoku.comFreemium

One of the busiest Sudoku sites online. Dailies, hints, notes, and a check for mistakes.

Open → f-puzzlesFree

The default web editor for Sudoku variants. Build a grid, send the link, or just solve.

Open → Killer Sudoku OnlineFree

Killer only. New grids by the day and the week, and they get meaner as they go.

Open → NYT SudokuFreemium

The New York Times grid for the day, easy in the morning, harder later.

Open → r/sudokuFree

Reddit's Sudoku board: the daily, a stuck thread, and chatter about who was faster.

Open → BrainBashersFree

Been free for years. A daily logic set, plus Sudoku variants, Kakuro and Nonograms.

Open → Daily Killer SudokuFree

One new Killer a day, plus a few extras. Nothing to pay.

Open → Killer SudokuFree

Killer Sudoku that's been around. An online solver, and a deep pile of old grids.

Open → Web SudokuFree

A plain page. Four difficulties, a timer, a check, and a print button.

Open → 247 SudokuFree

Four levels, and there's a grid waiting whenever you show up.

Open → PuzzleMixFreemium

Gareth Moore's site: Sudoku, then Slitherlink, Nurikabe, Futoshiki, Calcudoku and Hanjie.

Open → SudokuPadFree

The variant player a lot of people use now, and it edits too. There's an app and a Steam build.

Open → BePuzzledFree

Forty-plus logic types, no account. Nonogram, Slitherlink, Nurikabe and Hashi share one door.

Open → Penpa+Free

A fat editor for Japanese types: lots of shapes and marks, and it will ingest a puzz.link.

Open → Sudoku KingdomFree

A large free pile, several difficulties, and you can start at once.

Open → Fed SudokuFree

Slovak daily Sudoku league — day and week boards, printable archives.

Open → Sudoku GameFree

Free Sudoku in the browser, several levels, a few stats, and it behaves on a phone.

Open → Sudoku99 (CN)Free

150k+ grids across twenty difficulty bands. Free, no signup, and Word printouts.

Open → Variant SudokuFree

A newer Chinese variant board, updated most days. Solutions drop into the players people already use.

Open → Sudoku.nameFree

Several languages, free. Technique notes, a few stats, and grids you can print.

Open → Sudoku KnackerFree

The Sudoku site a lot of German speakers keep open. Daily grids, quietly solid.

Open → Grandmaster PuzzlesFree

Thomas Snyder's own handmade Sudoku and variants — world-champion difficulty, not generated filler.

Open → Live SudokuFree

Free play with hints and pencil marks, and a head-to-head mode if you want company.

Open → Sudoku 100Free

A few difficulties, and a fresh grid each day.

Open → HALAS (Czechia)Free

Czech logic-and-Sudoku association — the national contest door.

Open → Daily SudokuFree

Marty's long-running daily Sudoku, plus monster grids and blank PDF sheets.

Open → OnlineSudokuFree

Web Sudoku across difficulties, with a logic-puzzle shelf and a daily door.

Open → Sudoku AustraliaFree

Australia's WPF member site — national Sudoku and puzzle selection notes.

Open → Sudoku Puzzle (Chinese)Free

Chinese interface, free, marks mistakes, and you can print the grid.

Open → Sudoku HomeFree

A busy Chinese hub: Killer and other variants, and people show up every day.

Open → Sudoku FansFree

An older Chinese Sudoku community — banks, a forum, and the odd contest.

Open → Sudoku CloudFree

Chinese site for play, a solver, printable PDFs, and a walkthrough if you want one.

Open → Shudu.oneFree

Chinese online Sudoku with daily printable sheets (answers included) and pen/pencil modes.

Open → GridPuzzleFree

Dozens of grid logic types in the browser, with progress tracking and dailies.

Open → Sudoku BMCXFree

Chinese generator and print tools — play a few boards or take paper home.

Open → Sudoku-CNFree

Free Chinese online Sudoku in four difficulties — open and play.

Open → Sudoku TodayFree

A daily plus a few variants. Clean, free, and the chrome comes in several languages.

Open → Premium SudokuFreemium

More tooling than a bare player, and members get a larger bank.

Open → Puzzle SudokuFreemium

Puzzle Team's classic Sudoku: daily grids and a deep bank, same feel as their other type sites.

Open →

Browse Sudoku →

Also on multi-type portals

KrazydadFree

Jim Bumgardner’s printable library. Sudoku and other books as PDFs — made for a bag and a pencil.

Open → Printable SudokuFree

Blank Sudoku sheets in every grade, meant for paper.

Open → Sudoku PuzzlesFree

Printable booklets with answers in the back — useful when you want the screen off.

Open → Janko.atFree

Otto Janko's German/English archive: hundreds of playable types, all free.