Sudoku has one rule — every row, column, and 3×3 box must contain the digits 1 through 9 exactly once — yet from that single rule flows a whole ladder of solving techniques. A good Sudoku never requires guessing. Here is how to climb from simple scanning to the logic that cracks the hardest grids.

1. Start by Scanning

Before anything fancy, scan. Pick a digit — say 5 — and look across the grid for rows, columns, and boxes that already contain it. Those lines eliminate cells, and often a box is left with only one square where the 5 can legally go. Work through the most common digits first; the ones already appearing several times are the easiest to place.

2. Pencil In Candidates

Once scanning stops yielding easy placements, switch to candidates — the small “pencil marks” listing every digit still possible in a cell. This is the single biggest leap in skill. With candidates written in, the puzzle stops being about memory and becomes about reading patterns. Every technique below operates on these pencil marks.

3. Naked Singles

A naked single is a cell with only one candidate left. It has nowhere else to go — fill it in. Placing it removes that digit from its row, column, and box, which often creates the next naked single. A chain of naked singles can unravel a surprising amount of the grid in one sweep.

4. Hidden Singles

A hidden single is sneakier: a cell may list several candidates, but if it is the only cell in its row, column, or box that can hold a particular digit, that digit belongs there — the other candidates are a distraction. Hidden singles are the most common “aha” in medium puzzles. Train your eye to ask, for each digit in a unit, “where can this go?” rather than only “what can go here?”

5. Naked and Hidden Pairs

When two cells in the same unit share the exact same two candidates — say both can only be 3 or 7 — those two digits are locked into those two cells. You can safely erase 3 and 7 from every other cell in that unit. That is a naked pair. Its mirror, the hidden pair, is when two digits can only appear in the same two cells of a unit; you can then erase all their other candidates. Pairs are the gateway to intermediate solving.

6. Pointing Pairs and Box-Line Reduction

Sometimes a digit within a box is confined to a single row or column of that box. Even without knowing which cell it lands in, you know it lives on that line — so you can remove that digit from the rest of the row or column outside the box. This pointing pair (and its reverse, box-line reduction) is how you break into genuinely hard puzzles.

7. Never Guess — Look Harder

A properly constructed Sudoku has exactly one solution reachable by logic. If you feel the urge to guess, it almost always means you missed a hidden single or a pair. Step back, pick a single digit, and re-scan every unit for it. The discipline of refusing to guess is what turns a frustrating puzzle into a satisfying one.

Practice Every Day

Technique is built through repetition. Play a fresh grid daily with the Daily Sudoku and deliberately name the technique you are using on each move — “that is a hidden single, that is a naked pair.” Naming them cements the pattern until you spot it on sight.

Keep your mind sharp: Daily Sudoku, Word Search, or the Daily Word Wheel.