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Play Sudoku online

Straight in your browser. Pencil marks, conflict detection, automatic resume. No sign-up and no adverts.

🆓 Free✏️ Pencil marks💾 Auto resume

📘 The four grids playable here are taken from the book SUDOKU, 100 grilles à résoudre et à télécharger, in French.

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Stuck? Work through this order

  1. Scanning, digit by digit
  2. Singles, one cell with one candidate
  3. Write the candidates, nothing follows without them
  4. Naked pairs and triples
  5. Hidden pairs and triples
  6. Pointing Pairs and Box Reduction
  7. X-Wing, Y-Wing, SwordFish
See the 13 tutorials →

How to play

Click a cell, then a digit on the keyboard or the pad. Your digits show in green, the given ones stay black.

Notes mode writes candidates small in the corner of a cell, exactly like pencil marks on paper. It becomes essential from medium level onwards.

Conflicts turn red as soon as the same digit appears twice in a row, column or box. Nothing stops you making a mistake, you are simply told.

Your game is saved in the browser: close the tab and you will pick it up where you left off.

🧭 The techniques, one by one

The Stuck? button names the technique of the moment. Here is the full map: every technique has its tutorial, with a video, a diagram on a real grid and an interactive exercise.

The six basic techniques

Naked pairsTwo cells, two digits, nothing else: both digits leave the rest of the unit. Hidden pairsTwo digits have only two cells left: those cells clear out everything else. Naked triplesThe naked pair with three cells, and a trap: the three digits are not always all present. Hidden triplesThe hardest of the basics to spot, and the one that unlocks the most. Pointing pairsIn a box, a digit only fits on one line: it leaves the rest of that line. Box reductionThe reverse: on a line, a digit only fits in one box, so it leaves the rest of the box.

The six advanced techniques

X-WingOne digit, two rows, two columns, four boxes: the columns lock. Sashimi X-WingThe X-Wing with a missing corner, which works all the same. SwordFishThe X-Wing over three rows and three columns. Y-WingThree two-candidate cells in a chain: the digit shared by both wings falls. XYZ-WingThe Y-Wing whose pivot carries all three digits. W-WingTwo twin cells joined by a strong link. This is the one that breaks the level 6 grid.

And beyond

X-Cycles and chainsChain reasoning, which covers the XY-Chain that grids 7 and 8 demand.

These grids are for practising what you have learnt. Every technique has its tutorial, with a video, an interactive exercise and a diagram on a real grid: see the 13 tutorials.

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