How to Play Sudoku: Rules, Notation, and Your First Solved Grid (2026)

1. The only three rules

Each row must hold digits 1-9 exactly once, each column the same, and each 3x3 block the same. That is the entire game — every technique is just these three rules applied with patience. If a move breaks any one of them, the build's conflict highlight tells you instantly, so beginners literally cannot practice wrong for long.

2. Read the board in row-column language

Call rows r1-r9 top to bottom and columns c1-c9 left to right: r4c7 means row 4, column 7. This notation turns vague staring into precise questions — instead of somewhere over there, you ask what can go in r4c7 given its row, column, and block. Use it from day one and every future technique reads like instructions, not riddles.

3. Your first solve: fill every naked single

On Easy, most cells start one candidate away from decided: scan each empty cell and count which digits its row, column, and block still allow. Whenever exactly one digit fits, place it — that is a naked single, and a fresh Easy board holds a dozen. Do one full pass of the whole grid placing only naked singles before trying anything cleverer.

4. Then hunt hidden singles

When naked singles dry up, flip the question: pick a digit and a unit, and ask which cell in that unit can still hold it. If a 7 fits nowhere in row 6 except r6c2, that cell is 7 even with five candidates scribbled in it — that is a hidden single. Each hidden single placed usually unlocks two more naked singles, so alternate the two hunts until the grid falls.

5. Use notes, hints, and conflicts as training wheels

Switch on Notes mode and pencil every candidate — visible candidates turn hidden singles into naked ones you can see. Spend one Hint per stuck point and reconstruct why that cell was forced before continuing. Treat every red conflict as a free lesson: undo, find the unit you misread, and that mistake never repeats. Three guided Easy solves like this, and the beginner tips take over from there.

FAQ

How long does a first game take?

Fifteen to thirty minutes on Easy with notes on. Speed comes later — the first three games are about learning the row-column-block reflex, not the clock.

Do I need to guess?

Never on Easy: every cell is logically forced if you find the right single. If you feel stuck, you missed a hidden single somewhere — scan digit by digit instead of cell by cell.

What do the red highlights mean?

A rule break: two identical digits sharing a row, column, or block. Undo the last placement and re-check that unit before continuing.

Which difficulty after the first win?

Stay on Easy until you finish without hints, then step to the next of the five difficulties up to Insane. The rules never change — only the givens shrink.

Where can I play it?

Right on this site's sudoku page. The game is a self-hosted modification of the MIT-licensed sudoku-play by EduardoProfe666; license and attribution are listed under the game.