The entire rulebook fits in one sentence
Fill the 9×9 grid so every row, every column and every 3×3 box contains the digits one through nine exactly once. That is the whole game. Every proper sudoku is solvable by logic alone — if you find yourself needing a coin flip, a clue you have already earned is being wasted.
Start where the board is nearly finished
The fastest progress comes from units that miss only one or two digits. Find the row, column or box with the fewest empty cells, list what is missing, and check where each missing digit can legally go. When a unit misses a single digit, its home is forced.
The same scan works per digit: pick the 5s, say, and look at each 3×3 box. Cross off rows and columns that already hold a 5, and a box left with one legal cell gives you a free placement. Repeat that pass with a different digit and the grid keeps opening.
Use pencil marks honestly
When a cell holds two or three candidates, write them down instead of holding them in your head — most of the games on our shelf have a note mode for exactly this. The discipline that matters is updating: the moment a digit lands in a row, column or box, erase it from the candidate lists it touches, or your notes will start lying to you.
Learn one pattern: the locked pair
If two cells in the same unit are the only ones that can hold the same two digits — say a 4 and a 7 — then those two digits live in those two cells, in some order. No other cell in that unit can be a 4 or a 7, which often clears candidates elsewhere and unlocks the next placement.
That single pattern is enough to finish most easy and many medium grids, and it teaches the shape of every advanced technique to come.
Second pattern: the pointing pair
Once locked pairs feel automatic, the next rung is the pointing pair — the same logic aimed at a box instead of a line. When every candidate for a digit inside a three-by-three box sits in a single row, that digit must land in that row, which means it can be erased from the rest of the row outside the box. Two erasures, zero risk, and suddenly a row you had written off has a single candidate again.
The reason to learn pointing pairs second is that they are the bridge to every harder pattern: X-Wings, locked triples, chains — they are all this same move (restrict where a digit can go) applied at larger scale. A beginner who has internalized pointing pairs reads an X-Wing explanation and recognizes the shape rather than memorizing it, which is the difference between techniques that accumulate and techniques that evaporate.
Three kinds of wrong, three kinds of fix
Every wrong digit in a beginner grid comes from one of three places, and each has its own fix. The rule error: a digit placed against the one-per-unit rule — the fix is the scan that should have preceded it, and slowing down removes the whole category. The reading error: the grid was read correctly but a candidate was missed — the fix is honest pencil marks, which turn a missed candidate into a visible one. The transcription error: right deduction, wrong cell — pure slippage, and the fix is simply placing digits deliberately rather than while thinking ahead.
Sorting your own mistakes this way does something subtle: it stops the feeling that sudoku is punishing you randomly. A rule error means read again; a reading error means mark again; a transcription error means slow down. Three named problems with three known fixes feel entirely different from one nameless fog of wrong digits — and beginners who name their errors stop making the same one twice.
When the grid seems stuck
Re-scan systematically instead of staring: run one digit at a time across all boxes, then check the row and column you have visited least recently. If the board is truly frozen, the cause is usually a stale pencil mark or a placement made on feel rather than logic — undo the last assumption and the contradiction normally resolves.
Choose your grid
Our sudoku shelf covers classic 9×9 grids at Medium difficulty and one Hard-labeled master set, plus variants with different input styles and skins: some want the cell picked first, others the number, and Emoji Sudoku swaps digits for faces. Every page lists its controls and devices, so try a couple and keep the one whose input feels natural.
