Minecraft wiki entry for Spawn, associated text: When the player first loads into the world or respawns, the game searches within the world spawn area and tries to place the player on a random grass block. Upon spawning, the player is placed on the highest valid spawn point block of the X and Z spawn coordinates, even if this would set the player above the maximum build height. However, if there are no valid spawn points but a grass block that was determined to be an invalid spawn point due to being blocked by a block above it (though the grass block would decay soon after), the game checks the closest two free spaces from below and the player spawns there. If there are absolutely no grass blocks, the player spawns directly at the world spawn point, which can even result in players spawning above the Void if there are no blocks at that location.