Chunk format

Chunks store the terrain and entities within a 16×384×16 area in the Overworld, and 16×256×16 in the Nether and the End by default. They also store precomputed lighting, heightmap data for Minecraft's performance, and other meta information.

Chunks are stored as tags in regional Minecraft Anvil files, which are named in the form r.x.z.mca. They are stored in NBT format, with the following structure (updated for 1.18):

In the Anvil format, block positions are ordered YZX for compression purposes.