"What is the 2-1-2 pattern in Minesweeper?"

"Three revealed numbers in a row reading 2-1-2, with a row of five unrevealed cells on one side. The cells directly under the two 2s are safe. The cell under the 1 and the two cells diagonally past each 2 are mines."

"Does the 2-1-2 pattern work against the edge of the board?"

"No. If the row of numbers touches the board edge at either end, the outer cells do not exist and the numbers cannot read 2-1-2. The pattern needs five unrevealed cells: one past each 2 and three directly under the numbers."

"How is 2-1-2 related to the 1-2-1 pattern?"

"Both come from the same 1-2-X rule. In 2-1-2 you apply it twice, reading outward from the 1 in each direction: each time, the cell past the 2 is a mine and the cell before the 1 is safe."

2-1-2 Pattern in Minesweeper (212 Explained)

By Mike Burn Published September 28, 2026

The 2-1-2 pattern is the lesser-known partner of the 1-2-1. When three numbers along a boundary read 2-1-2, the answer is always the same: the cells under both 2s are safe, and there are three mines, one under the 1 and one diagonally past each 2.

Try spotting 2-1-2s: Play a free game on Minesweeper Blast and watch the edges of your opened areas.

How the 2-1-2 Works

Picture three revealed numbers in a row, 2, 1, 2. The cells to the left and right of them in the same row are already open, and there is a line of unrevealed cells on one side. Because each number touches its diagonals, the unrevealed line is five cells long: one past each 2 and three directly under the numbers.

. . . . .
. 2 1 2 .
A B C D E

. = already revealed, A–E = unrevealed cells.

Each “2” sees three unrevealed cells and needs two mines among them: the left 2 sees A, B, C and the right 2 sees C, D, E.
The “1” sees three unrevealed cells, B, C and D, and needs exactly one mine.

Only one arrangement satisfies all three numbers:

Cell	A	B	C	D	E
Status	Mine	Safe	Mine	Safe	Mine

Flag A, C and E. Click B and D.

Why It Works: The Constraint Logic

Each unrevealed cell is either 0 (safe) or 1 (mine). The three numbers give three equations:

Left “2”: $A + B + C = 2$
The “1”: $B + C + D = 1$
Right “2”: $C + D + E = 2$

Subtract the middle equation from the left one: $A - D = 1$. The only way two cells can differ by 1 is $A = 1$ and $D = 0$. So A is a mine and D is safe.

Subtract the middle equation from the right one: $E - B = 1$, so E is a mine and B is safe.

Put $B = 0$ and $D = 0$ into the middle equation: $C = 1$. C is a mine.

Result: $A = 1$, $B = 0$, $C = 1$, $D = 0$, $E = 1$.

The Shortcut: It’s the 1-2-X Rule Twice

If you know the 1-2-X rule, you already know 2-1-2. Read outward from the 1:

1 then 2 to the right: the cell past the right 2 (E) is a mine, and the cell before the 1 (B) is safe.
1 then 2 to the left: the cell past the left 2 (A) is a mine, and the cell before the 1 (D) is safe.

Once B and D are safe, the 1 has only one cell left, C, so C is the mine.

Where to Look for 2-1-2

Along the Edge of an Opened Area

The most common spot. When you open a region, its border often has a straight run of numbers facing a line of unrevealed cells. Any time the border reads 2-1-2 and the row continues past both 2s, the pattern applies.

After Reduction

Higher numbers with flags next to them often hide a 2-1-2. Subtract the flags each number touches:

Original	Flags	Effective
3-2-3	One flag directly under the middle number (it touches all three)	2-1-2
3-1-3	One flag diagonally past each 3 (each touches only that 3)	2-1-2

See Pattern Reduction for the full technique.

Not Against the Board Edge

2-1-2 cannot sit in a corner or flat against a side wall. Its outer mines (A and E) need room past each 2. If the row of numbers runs into the edge of the board, you are looking at a different configuration.

Practice Scenarios

Scenario 1: Basic 2-1-2

? ? ? ? ?
. 2 1 2 .
. . . . .

The five ? cells above the numbers follow the pattern: mine, safe, mine, safe, mine. Flag the 1st, 3rd and 5th cells. Click the 2nd and 4th.

Scenario 2: Vertical 2-1-2

? . .
? 2 .
? 1 .
? 2 .
? . .

The pattern works in any direction. Reading down the unrevealed column: mine, safe, mine, safe, mine.

Scenario 3: Hidden by a Flag

? ? ? ? ?
. 3 2 3 .
. . F . .

The flag sits under the middle number, so it touches all three numbers. Subtract it from each: 3-2-3 becomes 2-1-2. The five ? cells are mine, safe, mine, safe, mine.

Common Mistakes

Forgetting the Outer Cells

Players often look only at the three cells directly under the numbers. Each 2 also touches the cell diagonally past it, so the pattern covers five cells, and two of the three mines are on the outside.

Confusing 2-1-2 With 1-2-1

They look like mirror images but resolve differently:

Pattern	Unrevealed cells	Result
1-2-1 (against a wall)	3	Mine, safe, mine
2-1-2 (open row)	5	Mine, safe, mine, safe, mine

Not Reducing First

A 3-2-3 or 3-1-3 does not look like 2-1-2 until you subtract the flags. Reduce each number by the flags it touches before you look for patterns.

1-2-1 Pattern: the mirror-image pattern, and the most common one in the game.
1-2-X Rule: the building block behind 2-1-2.
1-2-2-1 Pattern: the four-number extension of 1-2-1.
2-2-2 Corner Pattern: what happens when three 2s wrap around a corner.
Pattern Reduction: how to reveal hidden patterns on busy boards.