World Primer Mod 1.12.2, 1.11.2 (An Important Server-Utility Mod)

The commands to run are set in the following config options. They can all be also configured via the in-game config menu:

• dimensionLoadingCommands – commands to run each time a dimension gets loaded
• earlyWorldCreationCommands – Commands to run on initial world creation before the spawn chunks have been generated or loaded. If dimension load tracking is enabled, then this happens even before any dimensions have been loaded/initialized yet.
• earlyWorldLoadingCommands – Commands to run every time the world gets loaded (ie. when the server is starting). These are run when the server is starting before any worlds have been loaded.
• postWorldCreationCommands – Commands to run on initial world creation after the spawn chunks have been generated and loaded.
• postWorldLoadingCommands – Commands to run every time the world gets loaded (ie. when the server is starting). These are run when the server has started and the overworld spawn chunks have been loaded.

There are also separate config options to enable or disable all of these, without having to remove all the commands if you want to temporarily disable them:

• enableDimensionLoadingCommands
• enableDimensionLoadTracking – enables tracking the number of times dimensions have loaded, and how many times the server has started (ie. how many times the world has been loaded).
• enableEarlyWorldCreationCommands – Enables early world creation commands, which are executed before any dimensions have been loaded and thus before any chunks have been generated or loaded
• enableEarlyWorldLoadingCommands – Enables early world loading commands, which are executed once at each server start, before any dimensions have been loaded
• enablePostWorldCreationCommands – Enables late world creation commands, which are executed after the dimension have loaded, and the overworld spawn chunks have been generated
• enablePostWorldLoadingCommands – Enables late world loading commands, which are executed once at each server start, after all the dimensions and also the overworld spawn chunks have been loaded.

In addition to these, there is also the enableDebugLogging option, which prints log messages from the various events, so it is easy to track what happens and when.

The dimension loading commands can be targeted to only run when a specific dimension load, by specifying the command like this:
worldprimer-dim-command <dim id> <the actual command>.
So for example:
worldprimer-dim-command 1 say The End dimension has loaded!

If you just give a command without the prefix, then it will be run every time ANY dimension loads, for example:
say Some dimension has loaded!

As of version 0.3.0, there is now also another dimension loading command variant, which can run the command on a specific number of dimension loads, or on any multiple of the given value.
Note: This variant requires the option enableDimensionLoadTracking to be enabled!
The syntax for these is:
worldprimer-dim-command-nth <dim id> <load count> <the actual command>

So to only run a command when the Nether loads for the very first time, you could use:
worldprimer-dim-command-nth -1 1 say The Nether has loaded for the first time!

Or when the End loads for the 6th time:
worldprimer-dim-command-nth 1 6 say The End has loaded for the sixth time!

To run a command on any multiple of the given value, prefix the value with a ‘%’:
worldprimer-dim-command-nth 1 %5 say The End has loaded a multiple of 5 times!

There is also support for substituting the dimension id, or the current world spawn coordinates into the commands.
The substitution strings are: {DIMENSION}, {SPAWNX}, {SPAWNY} and {SPAWNZ}. They also support simple addition and subtraction of constant numeric values.

So for example, you can now do this in postWorldCreationCommands, to make the player spawn in a 5x5x3 room underground:
gameRule spawnRadius 0 (this sets the spawn fuzz to 0, so the player fill spawn exactly in the center of that small room, and not randomly somewhere around that spot, on the surface)
setworldspawn {SPAWNX} 7 {SPAWNZ} (moves the world spawnpoint down to y = 7)
fill {SPAWNX}-2 7 {SPAWNZ}-2 {SPAWNX}+2 9 {SPAWNZ}+2 minecraft:air (makes a 5x5x3 room of air inside the ground, or whatever happens to be at that spot)

As of newest version there is a new built-in command:
worldprimer-load-chunks <chunkXMin> <chunkZMin> <chunkXMax> <chunkZMax>.

It can be used to load a range of chunks so that some other commands can actually work. For example, the vanilla /fill command only works in loaded chunks, so this can be used to load the chunks before executing the fill command. The chunks are also immediately queued for unloading, so they shouldn’t stay loaded even until the next world save happens (every 45 seconds), but instead, unload on the next game tick.

The coordinates are chunk coordinates (so block coordinates divided by 16). The range is inclusive, meaning from the minimum up to and including the maximum.
Note that this isn’t an actually registered command, and is thus not usable via chat/server console, but instead, it’s only used internally if found in one of the configured commands.

Here is an example of how to build a bedrock box at 0,0 in the End dimension when it loads for the first time. These would be added as dimensionLoadingCommands:
worldprimer-dim-command-nth 1 1 worldprimer-load-chunks -1 -1 0 0
worldprimer-dim-command-nth 1 1 fill 10 0 10 -10 7 -10 minecraft:bedrock
worldprimer-dim-command-nth 1 1 fill 9 1 9 -9 6 -9 minecraft:air
worldprimer-dim-command-nth 1 1 say Finished building your box!