Each cell checks its eight neighbours once per generation. A live cell with fewer than two live neighbours dies from underpopulation, one with two or three survives, and one with more than three dies from overpopulation. A dead cell becomes alive when it has exactly three live neighbours. Every cell updates at the same time.

B3/S23 is a compact way to write Conway's rules. B3 means a dead cell is born with exactly three live neighbours. S23 means a live cell survives with two or three live neighbours. Any other neighbour count leaves a dead cell dead or causes a live cell to die.

Click cells on the grid to draw an initial pattern, or choose Random to fill about 30 percent of the board. Start advances the simulation every 200 ms and Stop pauses it. Step advances exactly one generation while paused, and Clear returns the whole board to empty cells.

You choose the starting cells, but after that the pattern evolves deterministically from the rules without turns, opponents or further decisions. That is why it is called a zero-player game. You can still pause this simulator, edit cells and start again to explore a different initial pattern.

This simulator uses a fixed 20 by 20 grid and does not wrap one edge around to the opposite edge. Positions outside the board count as having no live cell. That finite boundary can change a pattern that reaches the edge, unlike the theoretical Game of Life on an infinite grid.

Draw a 2 by 2 square for a block that stays still, or three cells in a straight line for a blinker that alternates between horizontal and vertical. To make a glider in a 3 by 3 area, fill the top-middle cell, the middle-right cell and all three cells in the bottom row. Place moving patterns away from the edge so the finite board does not cut them off too soon.