Borderline

One world size for every dimension.

Borderline reads the overworld world border and applies scaled borders to the Nether and End, so a single world size governs all three dimensions. It runs entirely on the server, needs no client mod, and uses only vanilla world-border packets, so unmodded players see the correct border wherever they are.

What it does

• Treats the overworld border as the source of truth.
• Derives the Nether border at one eighth of the overworld size, and the End border at one half (both configurable).
• Matches the overworld border center in every dimension, letting vanilla apply the Nether's 8:1 coordinate scale.
• Re-derives the Nether and End borders on server start, whenever the overworld border changes (including a plain /worldborder set), and on demand with a command.
• Pushes each player the border of the dimension they are in, using vanilla packets, so clients without the mod render the right border in the Nether and End as well.
• Remembers the last world size set through the mod and re-imposes it on the overworld at every start.

For example, with an overworld size of 10000 blocks:

Why

Vanilla links the overworld border to every other dimension at a 1:1 scale: set it to 10000 and the Nether border is also 10000, which is eight times larger than the Nether's coordinate scale implies. Vanilla also only ever tells clients about the overworld border, so a per-dimension border needs the server to send the right one to each player.

Borderline fixes both: it derives proportional borders and keeps every client in sync, without requiring anyone to install anything.

It only manages the world border. It does not generate, delete, or otherwise alter terrain, and it adds no blocks, items, entities, or registry entries.

Installation

1. Install Fabric (with Fabric API) or NeoForge for Minecraft 1.21.1.
2. Put the mod jar in the server's mods/ folder.
3. Start the server.

Use the universal jar on either loader, or the matching loader-specific jar if you prefer. The mod is server-side only: clients do not need it, and vanilla clients can see and honour the borders it sets.

Single-player works too, because the integrated server runs the same code. The commands need cheats enabled (permission level 2), just like vanilla /worldborder.

Commands

All commands require permission level 2 (operator).

/borderline set takes a diameter, exactly like vanilla /worldborder set.

Configuration

The config lives at config/borderline.json and is created with defaults on first run.

{
  "enabled": true,
  "skipWhenUnbounded": true,
  "worldSize": null,
  "nether": { "enabled": true, "sizeScale": 0.125, "centerScale": 1.0 },
  "end": { "enabled": true, "sizeScale": 0.5, "centerScale": 1.0 }
}

The default scales are 0.125 for the Nether and 0.5 for the End. Set a dimension's enabled to false to leave its border untouched.

How it works

• The overworld border is the input. Borderline attaches to its changes, so any overworld border update is reflected in the other dimensions immediately.
• The Nether and End borders are not persisted by vanilla, so Borderline re-applies them at every start, and from the saved worldSize when one is present.
• Because vanilla only sends the overworld border to clients, Borderline sends each player the border of their current dimension with vanilla packets on change, on join, on respawn, and on dimension change.

Notes

• A plain /worldborder command still edits the overworld border; Borderline picks up the change and re-scales the Nether and End.
• Do not run another mod or plugin that also owns the world border for the same dimensions, or the two will fight over it.
• The mod changes the border only. It does not pre-generate chunks inside it.

Compatibility

• Minecraft 1.21.1
• Fabric and NeoForge
• Server-side only; no client installation required

Links

• Source and issues: https://github.com/retiredroca/Borderline

License

All Rights Reserved (ARR). Copyright (c) 2026 Retired Roca. See the LICENSE file in the repository.