Attribute Modifier (Data Type)

An Object describing how a single numerical value should be modified. Used by both vanilla-attribute powers (apoli:attribute) and by resource operations (apoli:modify_resource, apoli:change_resource alias). One data type, both call sites.

Why one type and not two#

Apace’s Apoli had AttributeModifier for the apoli:attribute power and a separate Modifier for apoli:modify_resource, which differed only in whether the attribute field was required. In this rewrite they’re one type with all-optional fields — the consuming power/action enforces which fields are required for its own purposes.

Fields#

Field	Type	Default	Description
operation	Attribute Modifier Operation		The operation performed by this modifier.
value	Float OR Expression	0	The modifier value. Also accepts the alias amount. When an Expression, evaluated each time the modifier is applied.
attribute	Identifier	optional	The vanilla attribute id this modifier targets. Required by apoli:attribute; ignored by apoli:modify_resource (since that targets a resource, not an attribute).
name	String	derived from power id	The vanilla AttributeModifier name (used for the modifier’s UUID seed).
resource	Identifier	optional	If set, use the value of this Resource (or Cooldown) power as the modifier value instead of value/value-as-Expression.
modifier	Attribute Modifier	optional	A nested modifier applied to the value of this modifier before it acts. Lets you scale a resource-driven value, etc.

Order of precedence for the input value#

When the modifier is applied to a current base/total, the “modifier value” fed into the operation is computed as:

1. If resource is set, start with that resource’s current value.
2. Otherwise, evaluate value (Float or Expression).
3. If modifier (nested) is set, run that modifier against the value from step 1 or 2 and use the result.

That single rule subsumes Apace’s separate “resource-as-value” and “modifier-of-modifier” forms.

Expression context: inside a value Expression, the value variable is bound to the unmodified input the modifier chain is being applied to — the current resource value in apoli:modify_resource, the attribute’s base value in apoli:attribute, or the incoming amount in modify_* powers. So "value": "value * 0.5" with "operation": "set_total" halves whatever comes in. All other Expression variables (health, xp_level, resource ids, …) are available too.

Examples#

Add 9 to a base value (used inside apoli:modify_resource):

"modifier": { "operation": "add_base_early", "value": 9 }

Multiply current value by 2 additive (Apace-style):

"modifier": { "operation": "multiply_base_additive", "value": 2 }

Use another resource’s value as the modifier value (the input is the value of example:resource):

"modifier": {
    "operation": "add_base_early",
    "resource": "example:resource"
}

Resource value, scaled down 0.001× via nested modifier (Apace-style nested modifier example):

"modifier": {
    "operation": "add_base_early",
    "resource": "example:resource",
    "modifier": { "operation": "multiply_total_multiplicative", "value": -0.999 }
}

Vanilla attribute apply (used inside apoli:attribute):

"modifier": {
    "attribute": "minecraft:generic.attack_damage",
    "operation": "addition",
    "value": 9
}

Expression value (a max-health bonus that scales with the player’s current XP level):

"modifier": {
    "attribute": "minecraft:generic.max_health",
    "operation": "addition",
    "value": "xp_level / 2"
}