Sudoku games and variants
- 4×4 Sudoku — Play 4×4 Sudoku free: fill the grid so every row, column and 2×2 box holds 1 to 4. Short puzzles solved with naked singles, plus hints, notes and undo.
- 6×6 Sudoku — Play 6×6 Sudoku free online: digits 1 to 6 in rows, columns and 2×3 boxes. Easy and Medium puzzles that bring in pointing pairs, with notes, hints and undo.
- Killer Sudoku — Play killer Sudoku free: cages with target sums replace most givens. Easy, Medium and Hard puzzles, cage-sum hints and a guide to forced combinations.
- Diagonal Sudoku — Play diagonal Sudoku free: both long diagonals must hold every digit once, on top of rows, columns and boxes. Four levels from Easy to Expert, with hints.
- Irregular Sudoku — Play irregular Sudoku free: nine jigsaw-shaped regions replace the 3×3 boxes. Five levels from Easy to Evil, with notes, hints and region-aware techniques.
- Hyper Sudoku — Play hyper Sudoku free online: four extra 3×3 windows must also hold every digit once. Four levels, Easy to Expert, with hints that name the technique used.
- Anti-Knight Sudoku — Play anti-knight Sudoku free: no two equal digits a chess knight's move apart, plus the usual rules. Four levels, Easy to Expert, with notes and hints.
- Daily Sudoku — Play today's Sudoku: one shared puzzle per UTC day, with the level set by the weekday from Easy to Evil. Build a streak that is stored only in your browser.
- 16×16 Sudoku — Play 16×16 Sudoku free online: sixteen symbols, 1 to 9 and A to G, in sixteen 4×4 boxes. Easy and Medium puzzles with notes, large digits and a two-row pad.
- Expert mode Sudoku — Expert mode Sudoku: Expert and Evil puzzles only, with no hints, no auto-notes, no mistake feedback and one attempt per puzzle. A test for strong solvers.
Sudoku Online has one flagship game, classic 9×9 Sudoku on the home page, and ten other boards that each change one real rule: a different grid size, extra regions, cages with sums, a knight’s-move restriction, a shared daily puzzle or a stricter expert mode.
Every board uses the same controls, hints and notes, and every stored puzzle has exactly one solution. This hub lists them all with what each changes and which levels it offers.
What counts as a variant here?
A board earns its own page only if it plays differently, not if it merely looks different. Each of the ten boards below changes the logic of the puzzle: the size of the grid, the shape of the regions, an extra constraint, or the way the puzzle is chosen. Themes, colors, large digits and the left-handed layout are settings that apply to every board, and they are described on the controls page.
The classic board on the home page is the starting point. It opens on a level chooser and is the only board that offers all five difficulty levels with a large pool of puzzles.
The boards at a glance
| Board | What changes | Levels | Stored puzzles |
|---|---|---|---|
| Sudoku 4×4 | A 4×4 grid, digits 1 to 4, 2×2 boxes | Easy | 30 |
| Sudoku 6×6 | A 6×6 grid, digits 1 to 6, boxes two rows by three columns | Easy, Medium | 150 per level |
| Killer Sudoku | Cages with target sums and no repeated digit inside a cage | Easy, Medium, Hard | 100, 100 and 70 |
| Diagonal Sudoku | Both main diagonals must hold every digit | Easy to Expert | 150 per level |
| Irregular Sudoku | Nine jigsaw regions replace the 3×3 boxes | Easy to Evil | 49, 80, 80, 80 and 45 |
| Hyper Sudoku | Four extra 3×3 windows must hold every digit | Easy to Expert | 150 per level |
| Anti-knight Sudoku | No equal digits a chess knight’s move apart | Easy to Expert | 150 per level |
| Daily Sudoku | One shared puzzle per UTC day, level set by the weekday | Easy to Evil | 60 per level |
| Sudoku 16×16 | A 16×16 grid with the symbols 1 to 9 and A to G | Easy, Medium | 60 per level |
| Expert mode | Expert and Evil only, no hints, no feedback, one attempt | Expert, Evil | 60 per level |
The counts are the number of puzzles stored on the site, each checked for a single solution. Classic has 1,000 per level across five levels. Levels are missing where the generator found no puzzle that needed the technique: the diagonal, hyper and anti-knight boards have no Evil level, because every puzzle generated for them could be solved at Expert or below. The site does not label a puzzle with a level it did not earn. The method is in how Sudoku difficulty is graded.
Which board should you try first?
- New to Sudoku: start with the 4×4 board to learn the idea in a minute, then the 6×6 board, then Easy on the classic board. The guided first puzzle walks through a real classic game.
- Comfortable with classic: add one extra rule at a time. Diagonal and hyper add regions that give you more to cross-check, and anti-knight adds a rule that is easy to forget.
- Want a different kind of reasoning: killer works with sums, and irregular asks you to read region shapes instead of boxes.
- Want a routine: the daily puzzle is the same for everyone each day and keeps a streak in your browser.
- Want a test: expert mode removes every aid. The 16×16 board is a long solve that rewards careful notes.
What is the same on every board?
All boards share one engine, so the controls, pencil marks, undo, hints and pause work the same way, except where a board removes them on purpose. Hints name the technique and are worked out from the digits you have placed. Your board and statistics are saved in your browser, not in an account. The controls page lists every key and setting, and the mobile tips cover touch play.
Where do the rules live?
The rules page states the classic rules and the one rule each board adds. The glossary defines the vocabulary, and the FAQ answers common questions. To see where these boards came from, read Sudoku variants through history. If a technique is new to you, the techniques hub has a lesson for each one, and the pillar guide on how to solve Sudoku puts them in order.