Online Minesweeper Game

A number in Minesweeper describes the cells around it, not the cell carrying the number. A revealed 2 is safe and says that exactly two neighboring cells contain mines. The aim is to uncover every safe cell in the minefield without opening a mine.

Neighbors include cells touching diagonally as well as those directly above, below, left and right. An empty revealed cell has no neighboring mines, so the area around it can open safely. The numbered boundary around an opening provides clues about the cells that remain covered.

Two basic deductions explain how those clues become useful:

• An open 1 with only one covered neighbor identifies that neighbor as a mine, because every other neighboring cell is already known to be safe.
• An open 2 with two neighboring mines already established makes every other neighboring cell safe. Simply placing two flags does not establish that their positions are correct.

More involved deductions combine overlapping clues. When two numbers share covered cells, any proposed mine positions must satisfy both counts. Flags help record suspected mines while you compare those clues, but they do not confirm a mine or change its location.

Chording is the shortcut for opening the remaining neighbors of a clue after placing the corresponding number of flags around it. It can replace several separate reveals, but an incorrectly placed flag can leave a mine among the cells being opened. The number of flags and the correctness of their positions are separate checks.

Board dimensions and mine count do not fully describe the challenge. Different mine arrangements produce different openings and deductions, even with the same settings. Some positions admit more than one arrangement consistent with every visible clue and may require a guess. A protected first move prevents an immediate loss; it does not promise that the rest of the board can be solved without guessing.

How to Use This Tool:

Choose the board settings before starting an attempt. Keyboard shortcuts work when the board or one of its cells has focus.

1. Choose a Board preset. Beginner, selected initially, has 9 columns, 9 rows and 10 mines. Intermediate has 16 columns, 16 rows and 40 mines. Expert has 30 columns, 16 rows and 99 mines. Select Custom board to enter your own values.
   Custom values must be whole numbers. Rows accepts 5 to 24, Columns accepts 5 to 30, and Mines must be at least 1 but less than the total number of cells. Correct any highlighted field before trying Start board again.
2. Enter a nonblank Seed, then select Start board. The default seed is mines-1. The field allows up to 96 characters, and spaces at the beginning and end are ignored.
3. Reveal a covered cell with Reveal selected. Click or tap a cell, or use the arrow keys to move and Enter or Space to activate it. On covered cells, these keys follow the selected Reveal or Flag mode. The first cell you actually open is safe. Scroll the board to reach cells outside the visible area.
4. Flag a suspected mine by right-clicking its covered cell or pressing F on the focused cell. For touch play, select Flag and tap a covered cell. Repeat the flagging action to remove the flag. A flagged cell must be unflagged before it can be revealed.
5. Chord an open number by clicking or tapping it, or by pressing C. Clicking an open number attempts a chord even while Flag is selected. When the neighboring flag count does not match, the message reports how many flags are needed and how many are present. Recheck the clues before changing the flags rather than placing them merely to satisfy the count.
6. Choose Pause or press P to hide the board while keeping its clues and flags. Switching tabs or windows also pauses play. Select Resume to continue, or End board from the paused board to finish the attempt without another reveal.
   Restart, called Restart board while paused, clears the current reveals and flags. It keeps the board settings and seed, but does not keep your progress.

Interpreting Results:

The dot symbol, ·, marks an opened cell with no neighboring mines. Safe cells shows how many safe cells have been revealed out of the total needed. Board cleared means every safe cell is open. Mine hit means a reveal or chord opened a mine. Board ended means you stopped the attempt voluntarily.

Mines − flags does not check flag positions. Zero means the number of placed flags equals the mine count, not that the flags are correct or the board is cleared. A negative value means more flags have been placed than there are mines.

Play is untimed. Actions counts game actions, not elapsed time or the number of cells opened. A lower count does not by itself demonstrate better deduction, especially after reviewing the mine locations. Game results are for recreation and have no monetary value.

Review board provides a read-only view with mines shown and incorrect flags marked ×. Unopened safe cells remain covered. Arrow keys move through the review, while Home and End jump to the first and last cell. If you ended before any reveal, no mines were placed, and earlier flags are marked × rather than checked against a generated minefield.

To revisit a layout, select Replay same seed and open the same first cell identified by row and column in the result. The opening cell is not selected automatically. New seed keeps the board settings while changing the seed, and Change setup returns to the board configuration.

Technical Details:

Each clue counts mines in the neighboring cells that lie within the board. An interior cell has eight neighbors, a non-corner edge cell has five, and a corner cell has three. Opposite edges are not connected for clue counting.

Reveals, flags and chords

Board-count formulas

Let R be the number of rows, C the number of columns, M the mine count and F the number of placed flags. The safe-cell target S is the number of cells left after subtracting the mines.

The displayed Mines − flags value B subtracts every placed flag, whether correct or incorrect.

All counts are exact whole numbers, with no rounding. The permitted mine count leaves S at least 1. Flag placement is not capped at M, so B can be negative.

Layout generation and repeatability

Mine placement waits until the first covered, unflagged cell is revealed. Exactly the selected number of mines is placed among the other cells, with no cell receiving more than one mine. Earlier flags neither influence placement nor use up the first-reveal protection.

Under the same rules, the board dimensions, mine count, seed and first revealed cell together reproduce the layout. Reusing only the seed is insufficient. Changing the opening cell changes which cell is protected and can change the mine arrangement. There is no guarantee that the resulting board can be completed without guessing.

What counts as an action

One action is added for a reveal that opens a covered cell, a flag placement or removal on a covered cell, or a chord with the required flag count. Revealing a mine still counts. An automatic opening of many cells belongs to the initiating reveal or chord rather than adding an action for every cell.

A matching chord counts even when no additional cells open. Reveals blocked by flags and chords with mismatched flag counts do not add an action. Moving focus, changing modes, pausing and resuming do not add actions either.

Worked Examples:

FAQ:

References:

• Gameplay, Minesweeper Online.
• Mines, Simon Tatham’s Portable Puzzle Collection.