Custom Worlds

Server-side mod to create, configure and teleport between multiple custom dimensions at runtime - each world with its own inventory, gamemode, difficulty, gamerules and worldborder. All via simple /cw commands. Vanilla clients can connect and use /cw tp - no client install needed.

Active Versions: 1.21.1 (NeoForge / Fabric)

See it in action

Features

• Runtime dimension creation - NORMAL, FLAT, NETHER or END generation, with optional seed.
• Per-world isolated state - every dim can have its own:
  • Default gamemode (applied on arrival)
  • Inventory pool (shared with other "shared" worlds, or fully isolated)
  • Gamerule overrides (with reset to revert)
  • Difficulty (custom dims only)
  • Worldborder (full /worldborder feature parity)
  • Public flag - let non-OP players teleport there
• Smart teleport - remembers each player's last position in every dim; safe-spawn detection on first visit (including Nether ceiling handling).
• Persistent across restarts - worlds, configs, player positions, inventories.
• Death respawn - dying in a custom dim respawns you there (unless your bed is elsewhere).
• Vanilla-client compatible - no client mod required.
• Deletion safety - /cw delete requires confirmation, wipes files and all related per-player buckets.

Commands

All commands hang off /cw. Public commands are visible to everyone; admin commands require the configured permission level (OP 4 by default).

Public

• /cw help - list commands available to you
• /cw tp <world> - teleport (admins: any dim; players: public worlds only)
• /cw list - list worlds (filtered by permission)

Admin - world management

• /cw create <name> <type> [seed]
  • Type: NORMAL, FLAT, NETHER, END
  • Examples:
  • /cw create myworld NORMAL
  • /cw create skyblock FLAT 12345
  • /cw create hellscape NETHER
• /cw delete <name> - confirm within 30 seconds by re-running the same command

Admin - per-world config (run from inside the dim)

• /cw config - show the current dimension's full config
• /cw config sharedinventory <true|false> - share inventory with other shared worlds, or use a fully isolated pool
• /cw config gamemode <survival|creative|adventure|spectator> - gamemode applied on arrival
• /cw config publicWorld <true|false> - allow non-OP players to /cw tp here
• /cw config difficulty <peaceful|easy|normal|hard> - per-dim difficulty (custom dims only)
• /cw config worldborder ... - same arguments as vanilla /worldborder, but applied to the current dim:
  • set <distance> [<time>], add <distance> [<time>]
  • center <x> <z>
  • damage amount <perBlock>, damage buffer <distance>
  • warning distance <blocks>, warning time <seconds>
  • get
• /cw config gamerule [<rule> [<value>|reset]]
  • No args: list all rules (overridden ones flagged with *)
  • <rule>: query
  • <rule> <value>: override the rule for this dim
  • <rule> reset: remove the override, revert to default

Permissions

The OP level required for admin commands is configurable in config/<save>/serverconfig/customworlds-server.toml:

permissionLevel = 4         # 0-4, OP level required for admin commands
maxWorlds = 0               # 0 = unlimited; hard cap for /cw create
deleteConfirmSeconds = 30   # 5-600

/cw tp and /cw list always remain available to everyone (filtered by the per-world publicWorld flag).

Inventory model

Each player has one inventory snapshot per "bucket":

• Shared bucket - used by every dim where sharedInventory = true (the overworld is shared by default). All shared worlds use the same inventory.
• Isolated bucket - one per dim where sharedInventory = false. The dim has its own private inventory pool; you keep your shared inventory intact when you go in and out.

Buckets persist on disk and survive restarts. Logging out from an isolated dim snapshots your inventory immediately.

Storage

Saved alongside the world data:

File	Purpose
customworlds.json	List of created worlds
customworlds_config.json	Per-dim config
customworlds_positions.json	Per-player, per-dim last positions
customworlds_inventories/<uuid>/<bucket>.dat	NBT inventory + XP snapshots
dimensions/customworlds/<name>/	Standard MC dimension data (chunks, entities, …)

Deleting a world wipes all of the above for that dim. Irreversible.

Compatibilities

Custom Worlds is compatible with Curios API (NeoForge) & Trinkets (Fabric), the inventory will sync when these mods are installed.

Limitations

• doDaylightCycle per-dim has no visible effect - game time is shared with the overworld through DerivedLevelData. Day/night follows the overworld.
• Per-dim difficulty only works on customworlds:* dims (it would conflict with vanilla's global difficulty for minecraft:* dims). For vanilla dims use /difficulty.
• Server restart recommended after /cw create - newly-created worlds run on a fallback tick loop until the next restart, after which they integrate normally. The mod tells you so on creation.
• Dynamic dimension registration uses reflection against MinecraftServer internals. Back up your save before updating NeoForge.

FAQ

Do my players need to install the mod? No. CustomWorlds is server-side only. Vanilla clients can connect and use /cw tp for public worlds.

Are the worlds compatible with vanilla? Yes. Custom dims reuse the vanilla OVERWORLD/NETHER/END dimension types, so vanilla clients recognize them without extra registry data.

What happens if a player is offline when their world gets deleted? On reconnect, vanilla falls back to the overworld spawn. They'll arrive with whatever inventory was saved in their player.dat at last logout.

Can I edit the JSON files manually? Yes - they're plain JSON. The loaders tolerate per-entry malformed data and log which entry was skipped.

Can I get more help about Custom Worlds ? Sure ! Join our discord at https://discord.gg/XNAeUSYswB