RegionCast

Keep a mirror server up to date by copying only the regions that changed, picked on a map.

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• A map of the world where each tile is one region file: red changed since the last copy, blue never copied, gold queued. Zoom in to pick single chunks.
• Click what you want, press Update, and the server restarts with the new terrain, points of interest and entities.
• The last 3 updates can be undone.
• Copies a few hundred MB instead of the whole world: on a real server only 59 of 1812 regions (407 MB of 8 GB) changed in a day.

Useful for creative copies, test worlds, render worlds, or a place to show a base without
letting people into the real server.

Installation

• Minecraft 1.21 / 1.21.1 or 26.3, Fabric and Fabric API. Java 21 for 1.21; Java 25 and Fabric Loader 0.19.5+ for 26.3.
• The jar goes on the destination server (the mirror). On your client it is optional and adds the map; without it everything works through /rc.
• The destination server must be able to read the source world’s files (a VPS or a dedicated machine; shared hosts like Aternos do not allow it). Mount it read only.
• Recommended: RCON on the source server, and something that restarts the mirror after it stops (an MCDReforged plugin is included).

Start the server once to create config/regioncast.properties, then set source_world and the
source’s RCON. Full setup in Setup in detail.

Usage

/rc                  open the map, or print the status if you cannot open one
/rc map              open the map (needs the client mod)
/rc status           what is out of date, what is queued, what backups exist
/rc here             queue the region you are standing in
/rc here chunk       queue only the chunk you are standing in
/rc add <dim> <x> <z>  queue one by index, dimension -1, 0 or 1
/rc scan             re-read the source
/rc list             what is queued
/rc clear            empty the queue
/rc run              copy it all, then restart
/rc backups          list the updates that can be taken back
/rc restore [n]      put one back, then restart

On the map: left click queues or unqueues, right click drag pans, scroll zooms. The queue survives
a restart.

Full documentation, configuration and technical details: README on GitHub.