🧮 Operations

What operations determine

An item's amount is only a modifier value; its operation determines how that value changes the attribute. CraftEngine processes the attribute's operations list from top to bottom in stages. A modifier participates only when its operation ID matches the current stage.

If operations is not configured explicitly, the default order is:

operations:
  - minecraft:add_value
  - minecraft:add_multiplied_base
  - minecraft:add_multiplied_total

The three built-in operations

Assume the value at the start of the current stage is base, the value before applying a modifier is current, and the modifier provides amount:

ID	Calculation for one modifier	Typical use
minecraft:add_value	current + amount	Fixed additions or subtractions, such as +8 Strength
minecraft:add_multiplied_base	current + base × amount	A percentage of the value at the start of this stage
minecraft:add_multiplied_total	current × (1 + amount)	Multiplying the current total

Here, base is the value when the current operation stage begins, not necessarily the original base field of the attribute.

Complete calculation example

Suppose an attribute has a base value of 10 and the equipment provides these modifiers:

- amount: 5
  operation: minecraft:add_value
- amount: 0.2
  operation: minecraft:add_multiplied_base
- amount: 0.1
  operation: minecraft:add_multiplied_total
- amount: 0.2
  operation: minecraft:add_multiplied_total

The calculation proceeds as follows:

1. add_value: 10 + 5 = 15;
2. The add_multiplied_base stage begins with base = 15, so 15 + 15 × 0.2 = 18;
3. add_multiplied_total: the two modifiers multiply in sequence, giving 18 × 1.1 × 1.2 = 23.76;
4. The attribute's constraint is applied last.

Multiple modifiers in the same add_multiplied_base stage all share the base captured at the start of that stage. Multiple modifiers in the same add_multiplied_total stage multiply one after another.

tip

Percentage amounts use decimals: 0.15 means +15%, while -0.2 means -20%. An add_multiplied_total amount of -1 reduces the result to 0; values below -1 may make the result negative, so they should normally be paired with a constraint.

Changing the calculation order

Declare operations explicitly in an attribute definition to change the order or disable an operation:

attributes:
  demo:might:
    base: 10
    operations:
      - minecraft:add_value
      - minecraft:add_multiplied_total
    constraint:
      min: 0
      max: 200

Operations not listed here are not calculated. In this example, an item modifier using minecraft:add_multiplied_base does not affect demo:might.

Custom operations

Assign an ID under attribute_operations and provide an expression:

attribute_operations:
  demo:add_capped:
    # Evaluated once for each modifier using this operation. Required
    expression: "MIN(current + amount, base * 2)"

attributes:
  demo:might:
    base: 10
    operations:
      - minecraft:add_value
      - demo:add_capped

Expression variables

Variable	Meaning
base	Value at the start of the current operation stage; unchanged throughout the stage
current	Value before applying the current modifier
amount	Amount provided by the current modifier

The expression's result becomes the new current. If evaluation fails, that modifier leaves current unchanged and a warning is written to the console. See Number Format → expression for expression syntax and common functions.

caution

Do not rely on the iteration order of modifiers within the same operation as a stable configuration interface. A custom expression should ideally produce the same result regardless of modifier order. If the calculation requires a strict sequence, define multiple operations and arrange them explicitly in the attribute's operations list.

Difference from synchronization operations

An attribute's sync entries also contain an operation, but that option controls which vanilla modifier operation is used when writing the result to a vanilla attribute. The attribute_operations section and the attribute's operations list on this page control CraftEngine's custom attribute calculation pipeline. Do not mix up the two.

Next, read Item Attribute Modifiers to apply these operations to actual weapons and equipment.