Block Condition Types

A block condition checks a single block position in a level and returns true or false. The level and position are supplied by whatever data table declares the condition, so the condition itself only describes what to check about the block at that position.

Block conditions are a Java (built-in) registry, so their type ids are fixed and a data pack cannot add new ones. type selects the built-in type and its value is one of the ids tabulated on this page, written with the mxt namespace. A data pack never adds or removes entries in this registry. Only Java code or the KubeJS bridge can introduce custom condition types — see the KubeJS API.

In the table below, a field name followed by ? is optional; every other listed field must be present. The Fields column lists the JSON keys taken directly from the type's codec.

Common Structure

A condition is a JSON object whose type field names the built-in type. All remaining keys are the fields declared by that type.

{
  "type": "mxt:block_tag",
  "tag": "minecraft:logs"
}

Because conditions are used as values inside other data tables, the same structure usually appears nested under a field such as block_condition:

"block_condition": {
  "type": "mxt:hardness",
  "comparison": ">=",
  "compare_to": 3.0
}

Anywhere a block condition is expected, an array of conditions is also accepted. The array is shorthand for mxt:and and passes only when every entry passes:

"block_condition": [
  { "type": "mxt:movement_blocking" },
  { "type": "mxt:height", "comparison": "<", "compare_to": 64 }
]

Comparison Fields

Several types compare a value against a number. The comparison operator and the number it is compared against, compare_to, always sit directly on the condition object as two separate keys, as in the example above. The comparison operators are ==, !=, <, <=, > and >=, and compare_to is always a plain number.

Datapack Visual Editor

The Datapack Visual Editor shows the field list of every type interactively, which is handy for checking a field name without reading the table here.

Condition Types

Type	Fields	Description
mxt:always_true	—	Always passes.
mxt:js	id, params?	Calls a block condition handler that was registered through the KubeJS bridge.
mxt:and	conditions	Passes only when every nested block condition passes.
mxt:or	conditions	Passes when at least one nested block condition passes.
mxt:not	condition	Negates a nested block condition.
mxt:chance	chance	Passes randomly with the given probability between 0 and 1.
mxt:constant	value	Always returns the given boolean value.
mxt:block_id	block	Matches the block at the position.
mxt:aura_range	aura	Tests the aura concentration at the position against per-aura requirements. aura maps an aura ID to an object with a required max and an optional min.
mxt:block_tag	tag	Matches the block against a vanilla or data pack block tag.
mxt:biome_tag	tag	Matches the biome at the position against a data pack biome tag.
mxt:hardness	comparison, compare_to	Compares the block's hardness.
mxt:height	comparison, compare_to	Compares the Y coordinate of the position.
mxt:light_level	light_type?, comparison, compare_to	Compares the light level at the position, optionally for one light layer.
mxt:slipperiness	comparison, compare_to	Compares the block's slipperiness.
mxt:blast_resistance	comparison, compare_to	Compares the block's blast resistance.
mxt:movement_blocking	—	Passes when the block blocks motion and has a non-empty collision shape.
mxt:adjacent	adjacent_condition, comparison, compare_to	Compares the number of adjacent blocks that match a nested block condition.
mxt:offset	condition, x?, y?, z?	Tests a nested block condition at a relative offset from the position.

mxt:aura_range

aura is a map from an aura to a requirement object with an optional min (default 0) and a required max, both of which accept a number provider. The condition passes when every listed pool lies inside its range.

mxt:light_level and mxt:adjacent

light_type accepts a vanilla light layer name, for example block or sky; when it is omitted the maximum local raw brightness is used. mxt:adjacent counts the blocks touching the position, and only positions in loaded chunks are considered.