One generally has two options for accessing the byte array of blocks: More information about the serialization format used by Java is available in the manual, however, the easiest way to edit the file is to use the classes already provided with the official minecraft-server.jar file. The version number represents the current format used to save the level. When uncompressed, the format of the file is as follows:Ī magic ID is a constant number used to identify the Minecraft file format. 255, the row below that at, from left to right, locations 256. The first 65536 sequential bytes of the array make up the top-most 256×256 "sliver" of the level, with the north-most row of bytes, from left to right, being at locations 0. The level's block values (material type, such as stone) are stored inside of a byte array inside of this class. Most of the block values are 0 (empty space), so, therefore, the size is reduced considerably by the compression, usually down to a few hundred kilobytes.Īfter un-gzipping the datafile (the player may simply decompress the file itself using a tool, which can decompress gzipped files), sequentially the datafile consists of the number 656127880 as 32-bit integer (0x27 0x1B 0xB7 0x88 in HEX), followed by the number 2 as a byte (0x02 in HEX), then followed by serialized Level Java classfile instance. The file is compressed using gzip, however. As this file is primarily raw level data, it can be quite large: a regular 256×256×64 sized level is 4 megabytes in size. The server level.dat file is where the Minecraft Server dumps the level information for permanent storage. Level files with bigger dimensions may differ in the amount of bytes.) (Note: in this example, a default server_level.dat is being used, with the size of 256×256×64. The file is compressed using gzip to save space (as the files can end up being reasonably large due to everything, even air being considered a block). The file can be backed up to save content which helps to protect constructions against griefers or to use the file for map editing. Server_level.dat is the name of the file used by the Minecraft Classic server for loading and saving the in-game map. This feature is exclusive to Java Edition.