Sudoku is the most loved logic puzzle in the world for a reason: simple rules, infinite depth. The board is a 9×9 grid divided into 81 cells. You're given a handful of digits to start; your job is to fill in the rest so that every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once. Every Sudoku has one and only one valid solution.

✖️ Diagonal X-Sudoku

The Diagonal variant adds two more constraints: the main diagonals (top-left to bottom-right, and top-right to bottom-left) must also each contain 1–9 once. Cells on the diagonals have additional peers and the puzzle solves with fewer givens. The diagonals are marked with a faint gold line on the board.

🧩 Jigsaw Sudoku

Jigsaw drops the 3×3 boxes entirely and replaces them with nine irregular regions, each in a distinct pastel colour. The row and column rules are unchanged, but the 1–9 constraint now applies to the coloured regions instead of boxes. Jigsaw puzzles look familiar but solve differently — your usual box-scanning techniques need adaptation.

🧠 Solving Techniques

Beginner puzzles often resolve through naked singles — a cell where 8 digits are already accounted for in its peers. Medium puzzles need hidden singles: a digit that can only fit in one cell of a particular row, column, or region. Harder puzzles need pencil-mark techniques: naked pairs/triples, pointing pairs, and at the extreme end X-Wing and swordfish patterns. Toggle ✏️ Notes mode to pencil candidates in any cell.

🎯 How to Play

Tap any cell to select it. The selected cell turns yellow, all its peers (same row, column and region) tint blue, and every cell with the same digit highlights darker blue — perfect for spotting where else a digit can go. Tap a digit on the numpad to fill, tap the same digit again to clear, or hit ⌫ to erase. Given cells (the puzzle's starters) are bolded and can't be edited. Long-press any cell on mobile to clear it.

⚡ Difficulty

Difficulty controls the number of given cells. Beginner ships with 45 givens (lots of obvious wins to get you started). Medium trims to 34 (the comfortable default). Cyborg ☠ bottoms out around 22 — the theoretical minimum for unique-solution Sudoku — and demands the full toolkit of advanced techniques. Daily challenges run at Medium so everyone can chase the streak.

Play Variant Sudoku free in your browser — no download, no sign-up. Three variants (Classic, Diagonal X, Jigsaw), seven difficulty tiers, a seeded daily challenge that's the same for every player worldwide, and shareable challenge links so you can pass your best time to friends and see if they can beat it.

Sudoku was popularised in Japan by Maki Kaji of Nikoli in the 1980s — though the format traces back to 18th-century Latin Squares and a 1979 Dell Magazine puzzle called "Number Place" by Howard Garns. The Diagonal X variant was added by Nikoli in the early 2000s; Jigsaw (sometimes called Squiggly Sudoku) emerged around the same time. This implementation uses a dig-from-solved generator with a uniqueness check at every step — every puzzle is guaranteed to have exactly one solution.

• Scan rows, columns and regions for naked singles. If a cell is missing only one digit, place it. These are free wins on easier puzzles and unlock cascades on harder ones.
• Hunt for hidden singles in each region. If a digit can only go in one cell of a row, column, or region, place it there — even if that cell has multiple candidates from its own perspective.
• Use the same-value highlight. Tap a filled cell to see every other cell containing that digit. Spotting patterns becomes far easier.
• Pencil notes early. On medium and above, fill notes for every cell up front. Then solve by elimination — far more reliable than scanning from scratch each time.
• Look for naked pairs. Two cells in the same row/column/region with identical 2-candidate notes mean those two digits must go in those two cells — eliminate them from every other peer.
• Save Check for when you suspect a mistake. It costs nothing and flashes wrong entries in red for 3 seconds. Don't burn it preemptively — use it when something feels off.
• Try Diagonal X after mastering Classic. The extra constraints let puzzles work with fewer givens — they look impossible but solve elegantly when you remember the diagonals.