Minecraft wiki entry for Server_level.dat, associated text: The player could deserialize the compressed .dat file directly back into an instance of a Level object inside of Java, thus having access to the instance of the Level object in exactly the same way the Minecraft Server does. This would allow the player to set the blocks, dimensions, spawn point and other aspects of the map directly by calling the methods on the instantiated Level object. Manual decompression is not needed before loading, because Java can compress and decompress gzipped files on the fly. To load the datafile back into an instance of the Level class, the player would need the class definition for the Level class. This is included with the minecraft-server.jar file. An example of this can be seen in the Development resources/Example Minecraft Classic Level Editing Class.