Fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1–9 exactly once. Start from the printed clues, find cells where only one digit can legally go, place it, and repeat — every proper puzzle is solvable by logic alone. No guessing, and no math.
Sudoku looks like a math puzzle. It isn't — there's no arithmetic at all. It's pure logic, and the whole rulebook fits in one sentence.
The one rule
Fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1 through 9 — each exactly once. That's it. If a digit would repeat in its row, column or box, it doesn't belong there.
The givens are your foothold
Every puzzle starts with some numbers already printed — the givens. They're fixed; you build the rest of the solution around them. A well-made puzzle (every puzzle here is generated this way) has exactly one solution, and you can always reach it by logic — no guessing required, ever.
Your first move
Pick a crowded region — a box that already has six or seven givens. For each empty cell, ask: which digits are already taken by this cell's row, column and box? When eight of the nine digits are ruled out, the remaining one is forced. Place it, and notice how it immediately narrows down the cells around it. Sudoku is a chain of these small certainties.
Pencil marks are half the game
When a cell has more than one possibility, jot the candidates in its corner — on paper with a pencil, here with note mode (or auto-notes, which fills every candidate in one tap). Each number you place erases candidates in its row, column and box, and cells collapse to a single candidate one by one.
Picking a difficulty
Difficulty isn't about harder rules — it's about the hardest step a puzzle needs. Start on easy, where every move is finding the one place a digit fits in a box. Move up when a grid stops feeling like a search and starts feeling like a stroll. Hard grids need pairs, and expert grids expect the bigger patterns from the next guide.
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