Declarations

A file is a list of declarations. Each one starts with its kind, a PascalCase word, then its name:

ItemTag gems = [diamond, emerald, amethyst_shard]

LootTable chests/gems {
  pools = [Pool(1..3, #gems)]
}

Write Kind name { fields } when the value is an object, and Kind name = value for anything else: a list, a helper call, a number. There is one spelling for each.

The Declaration kinds page lists every kind. Lowercase words such as const, let and for are not kinds: they declare values the compiler works with, and never write a file. See Constants, templates and loops.

Names and ids

A declaration's name is its id without the namespace. Names can have folders: chests/gems in the namespace gems is gems:chests/gems, and a LootTable of that name is written to data/gems/loot_table/chests/gems.json.

Where a field takes an id, write the name bare. A bare name means the project's own declaration when there is one, and the vanilla one otherwise, so diamond is minecraft:diamond and #gems is your ItemTag gems. Write minecraft: only to reach vanilla when the project has a declaration of the same name.

Different kinds can share a name, such as a Recipe and a LootTable both called gem_block. Two declarations of one kind with the same id are an error, except tags, which merge.

Namespaces

A file starts in the namespace from mms.json. A Namespace line changes it for the rest of that file:

Namespace minecraft

/** Adds to vanilla's swords tag. */
ItemTag swords = [diamond_sword]

Several at once

Kinds whose declarations carry no value take a comma list, which declares each name:

JigsawHole room_exit, hall_entry, hall_exit
Objective wins, losses

Doc comments

A /** ... */ comment right above a declaration documents it. The text is Markdown, and hover shows it on the declaration and on every use, including ids inside commands. JSDoc tags such as @param, @returns and @deprecated are understood:

Objective found

/**
 * Gives a player their reward and counts it.
 *
 * @param count how many diamonds to give
 * @deprecated use `reward_all`
 */
Function reward(count: int) {
  /give @s diamond ${count}
  found[@s] += 1
}

A @deprecated tag makes every use a deprecated lint warning. Getting started lists every tag.

Names made from values

Inside a top-level for or a Blueprint's emit, a name can be a template, so one declaration writes many real ids:

const colors = [red, green, blue]

for c in colors {
  /** A ${c} banner from wool. */
  Recipe ${c}_banner_from_wool = Shaped(["WWW", "WWW", " S "], { W = "${c}_wool", S = stick }, "${c}_banner")
}

That declares red_banner_from_wool, green_banner_from_wool and blue_banner_from_wool. Each is an ordinary id: go to definition, find references and rename all work on it. See Constants, templates and loops.