Function (Java Edition)

For the command, see Commands/function.

See also: Function (Bedrock Edition)

Functions are data pack files, allowing players to run lists of commands. Being text files, they are easily modifiable and less likely than command blocks to induce lag when used in large quantities.

This page covers how functions are defined and invoked in Java Edition.

Definition

A function is a text file with the file extension .mcfunction. The recommended encoding for function files is ANSI encoding (without BOM).

Function files belong in the following folder of a data pack's structure, highlighted below:

• (data pack name)
  • pack.mcmeta
  • pack.png
  • data
    • (namespace)
      • advancements
        • (advancement).json
      • functions
        • (function).mcfunction
      • item_modifiers
        • (modifier).json
      • loot_tables
        • (loot table).json
      • predicates
        • (predicate).json
      • Further folders…

As with all other data pack files, the functions folder may also contain subfolders to further organize the function files within a namespace. These subfolders must be referenced when invoking the function.

Testing the function system. Three /tellraw messages and one /give command were used in this simple function.

Within the .mcfunction file, one valid command is placed per line, without the usual forward slash (/). Players can add comments within the function text file by beginning a line with #. Multiple spaces between command arguments are not allowed but a line can have tabs and spaces before and after the command.

Allowed commands

Individual commands in functions can be longer than the 32,500 character limit in command blocks but the total number of commands run inside a function will still obey /gamerule maxCommandChainLength, which is 65,536 commands by default; any commands beyond this limit will be ignored.

In a singleplayer or a LAN world, like a command block, a function can run any command that is no more restrictive than permission level 2.

On the default multiplayer software, a function can run any command that is no more restrictive than the permission level prescribed in function-permission-level setting in server.properties.

Invocation

Functions can be invoked in several different manners from other data pack files.

Invocation from commands

Functions can be invoked using the /function command.

A single function can be invoked by specifying its resource location.

Unlike other data pack files, functions are supported by tags, allowing them to be grouped together. /function also accepts a function tag's resource location, invoking all listed functions.

Invocation from advancements

Advancements can run a function once as a reward for completing them. The commands in the function are run through the player who completed the advancement.

Reward functions are called within advancement JSON files using the following format:

{
  "rewards": {
    "function": "namespace:subfolder/function"
  }
}

Invocation from function tags

Functions can be grouped together using function tags.

In addition, there are two function tags within the minecraft namespace that have special behaviour:

• Functions listed in the minecraft:load tag will run when the world is loaded, or when the server is started. Listed functions will also run whenever the data pack is reloaded.
  • These functions run before the player joins the world, meaning any target selectors will find no players. Therefore, commands like /tellraw and /title will not show to any player.
• Functions listed in the minecraft:tick tag will run at the beginning of each tick, repeating every tick.

Note: The first instance of functions tagged minecraft:tick will run before minecraft:load runs. This means that when reloading or loading, the order of execution is tick, load, tick, tick, tick, …

When invoked:

Functions will run all their commands in a single tick and other functions called from within will also run their commands in the same tick as their parent. Functions will use the execution context of whatever called the function. This includes executing entity, as well as execution position, rotation, dimension, and anchor. Contextual parameters are preserved for all the commands in the function unless explicitly changed by /execute.

For example:

execute as @p at @s run function foo:bar

# function foo:bar
teleport @s ~ ~5 ~
setblock ~ ~-1 ~ emerald_block
execute at @s run setblock ~ ~-1 ~ diamond_block

When invoked, this function will teleport the nearest player 5 blocks up, place an emerald block one block below their original position before the teleport, and place a diamond block one block below their new position after the teleport.

As seen in the above example, contextual parameters can be changed as usual by their respective /execute sub-commands.

History

Java Edition
1.12		pre1			Added functions.
		pre3			Commands are no longer allowed to begin with a / (forward slash)
					Comments can now only be preceded with #; using // is no longer allowed
		pre4			Added new arguments to the /function command: [if|unless] [selector]
		pre6			Skipped functions (when a conditional fails) are now considered failures when used in commands.
1.13		17w43a			Custom functions have been moved into data packs.
		17w45a			Functions are now completely parsed and cached on load.
		17w49b			Removed /gamerule gameLoopFunction.
					Function can now be tagged.
					Functions tagged in tick now run every tick in the beginning of the tick.
		18w01a			Functions tagged in load now run after (re)loading the datapack.
1.14.4		pre4			Added function-permission-level to server.properties

Issues

Issues relating to "Function" are maintained on the bug tracker. Report issues there.