Seed (level generation)

A seed is a code used in Minecraft's world generation process. Each world has its own seed value which is used to keep generated terrain consistent, as generation is pseudo-random. Prior to Beta 1.3, seeds were automatically generated per-world. Since then, the player can input their own seed, which is not limited to numbers due to the use of the Java function. For instance, a seed of "abc" is converted to the numeric value 97&times;31² + 98&times;31 + 99 = 96354.

Contrary to common belief, using a biome name (i.e. tundra, desert, forest, etc.) as the seed does NOT always result in the creation of a world with primarily that biome, nor is it guaranteed you will spawn in said biome when the map is generated. Seeds also determine the entire landscape, not just the area near the spawn.

Using the same seed to generate two separate worlds will generate the same terrain consistently, even on different systems. As such, seeds can be shared by players to generate the same world between them. However, the player's initial spawn point will be random; it is not tied to the seed value.

If you leave the seed field blank, the game will use the time (computer clock) as a seed. Leaving the seed field blank will not produce the same map every time.

The seed will only influence the numbers returned by the terrain generator, and won't influence its underlying behavior. For instance, there is no random seed that will give you a world with lava instead of water, or a entirely desert world.

It should be noted, however, that if you use words or phrases as a seed input, you'll be restricted to a small fraction of the possible worlds in minecraft, due to the datatypes used for the seed and Java  function. You'll only be able to access around 4 billion possible worlds by using string input. Using pure numbers or letting Minecraft generate the world will give you access to the full set of possible worlds, which is around 18 quintillion. See the discussion page for details.