Minesweeper patterns and strategy

Read the opening, then work its rim

The start cell is always a zero, so the first tap opens a whole region and stops at a ring of numbers. A number counts the mines among its eight neighbours. On the rim of the opening most of those neighbours are already open, so the rim is where the first deductions are. Work your way around it instead of jumping across the board.

The two one-number rules, and chording

All mines: if a number has exactly as many covered neighbours as its value, every one of them is a mine. All safe: if a number already touches as many flagged mines as its value, every other covered neighbour is safe.

The second rule is what chording is for: tap a number whose flags already account for it (or click it with both mouse buttons) and all its other neighbours open at once. Chord only around flags you have proved. A wrong flag makes the chord open a mine.

The 1-2-1 pattern

Three numbers in a row, 1, 2, 1, along a straight edge of covered cells. The 2 needs two mines among the three cells beside it. If the middle cell were a mine, it would satisfy both 1s at once, and the 2 would be one mine short. So the middle cell is safe, and the two mines sit beside the two 1s.

The cells just past each end come free too: each 1 has used up its mine. Against a flat covered edge, 1-2-1 always reads the same: mine, safe, mine.

The 1-2-2-1 pattern

Four numbers, 1, 2, 2, 1, along a covered edge. The mines sit beside the two 2s, and the cells beside the 1s are safe.

The proof is a subtraction. The first 2 sees one covered cell the first 1 does not (beside the second 2), and the 1 sees one cell the 2 does not (just past the end). The 2 needs one more mine than the 1, so its extra cell is a mine and the 1's extra cell is safe. The same from the other end puts a mine beside the first 2. Each 1 is then satisfied, and the cells beside them are safe.

The 1-1 against a wall

Two 1s side by side, the first one against the edge of the board. The first 1 has only two covered cells, so its mine is one of those two. The second 1 sees the same two cells plus one more, and its one mine is already among them. So the third cell is safe.

This is the plainest case of the rule behind every pattern above: when all of one number's covered cells are also another number's, subtract. If the counts are equal, the extra cells are safe. If they differ, the extra cells hold exactly the difference.

Count the mines at the end

The counter above the board shows how many mines are left. Late in a game it settles cells no number reaches: when every mine is flagged, all the covered cells left are safe, and when the mines left equal the covered cells left, each one of them is a mine.

Why you never have to guess here

On a random board the first click can hit a mine, and the last cells can be a true 50/50. Our generator plays every board with the deductions in this guide before it is served and throws away any board they cannot finish from the start cell. So when you are stuck, there is always a provable move: look for two numbers that share covered cells, and subtract one from the other.

Questions

What is the 1-2-1 rule in Minesweeper?

Three numbers 1, 2, 1 in a row along a covered edge mean a mine beside each 1 and no mine beside the 2. The middle cell cannot be a mine: it would satisfy both 1s and leave the 2 one short.

Is Minesweeper always winnable?

Random boards are not; some end in a 50/50 that no logic can settle. Every board on this site is generated and checked so that logic alone clears it from the marked start cell.

What is chording in Minesweeper?

Tapping a number that already has all its mines flagged opens all its other neighbours at once. It saves taps, but it trusts your flags, so chord only around flags you have proved.

How do I know where a mine is?

Find a number whose covered neighbours equal its value (all of them are mines), or two numbers that share covered cells and subtract one from the other. The diagrams above show both on real boards.