Megastructure block

The block works like the vanilla structure block with two major changes. It captures a whole chunk-sized area in width and length, and its height covers the full height of the structure area. Structures are serialized in chunk-sized parts, each written as a separate NBT file, with a master file holding the header data needed to reassemble them into one megastructure when they are loaded back into the world.

A saved megastructure is identified by a minecraft:mgst prefix in its header. The block adds that prefix automatically to the name entered, so a structure named bigcastle becomes minecraft:mgst bigcastle, and a custom namespace can be used instead. A toggle controls whether special blocks such as air and entities are saved. Tests reached 100 by 100 blocks across 7 by 7 chunks; the author notes larger sizes are untested.

Megastructure block requires the Megastructure block worldgen dependency, which supplies the logic that spawns megastructures during generation. It is not a standalone structure tool: the mod runs on NeoForge only, for 1.21.8 – 1.21.11, and the latest file is 1.0b for 1.21.11, released 2025-12-28 on the beta channel. The client needs the mod, while the server may run without it. The code is open source under the GNU General Public License v3.0 only.