Recipe Capability Reference

MBD2 21.1.1

The core capability rows below map directly to these built-in machine handlers.

The registry name is the stable key used by codecs and MBDRegistries.RECIPE_CAPABILITIES.get(name). The trait type is what a machine must contain for normal handling.

Core capabilities

Registry name	Java content type	Trait type	KubeJS builder	Important behavior
item	SizedIngredient	item_slot	inputItems, outputItems	Matches item/tag candidates and amount; output must be insertable
item_durability	SizedIngredient	item_slot	inputItemsDurability, outputItemsDurability	Amount represents durability handled by the durability handler
fluid	SizedFluidIngredient	fluid_tank	inputFluids, outputFluids	Matches fluid/tag and amount; tank filters and IO still apply
forge_energy	Integer	forge_energy_storage	inputFE, outputFE	FE input extracts from storage; output receives into storage
entity	EntityIngredient	entity_handler	inputEntities, outputEntities	Supports entity types/tags, count, and optional NBT

An item-slot trait returns both item and durability handlers. A filter, side capability IO, recipe handler IO, and automatic IO are independent settings: allowing a pipe to insert does not automatically make the trait a recipe input.

Optional capabilities

Registry name	Dependency	Trait	KubeJS methods	Content meaning
mek_chemical	Mekanism	chemical_tank	inputChemicals, outputChemicals	ChemicalStackIngredient parsed from chemical strings
mek_heat	Mekanism	mek_heat_container	inputHeat, outputHeat	Heat amount as double
create_rotation	Create	Create rotation trait	input/outputRPM, input/outputStress	Tagged union: RPM requirement/generation or stress requirement/generation
pneumatic_pressure_air	PneumaticCraft	pneumatic_pressure_air_handler	pressure and air methods	PressureAir records whether the number is pressure or air volume
pneumatic_heat	PneumaticCraft	pneumatic_heat_exchanger	inputPNCHeat, outputPNCHeat	Heat amount as double
natures_aura	Nature's Aura	aura_handler	inputAura, outputAura	Aura amount as integer
ars_source	Ars Nouveau	ars_source_storage or ars_nearby_source	inputSource, outputSource	Source amount as integer; the two traits are mutually exclusive

Optional registrations use @LDLRegister(modID = "..."), so the capability is absent when the dependency is not loaded — and the matching KubeJS builder method throws. Guard the call in a pack where the mod can be absent.

Recipe-viewer widget IDs

uiName binds a content entry to a named widget in the recipe display UI. When it is empty, MBD2 matches the default generated ID:

@<capability>_<io>_<index>      e.g. @item_import_0, @fluid_export_1

<io> is the IO's display name — import for IO.IN, export for IO.OUT.

Set uiName only to override that mapping — for example to send a bonus output to a widget of your own. An explicit uiName is matched as a substring, not as an exact ID; see Slot Names and the Recipe Viewer UI for that, for the reserved @progress_bar / @duration / @condition / @custom_data elements, and for how a Trait declares the slot names slotName is matched against.

Routing fields

builder.slotName("hot_side")
    .input(HeatUnitsCapability.CAP, 500)
    .slotName(null)
    .uiName("@heat_input")
    .output(HeatUnitsCapability.CAP, 50);

Fluent fields remain active until changed. The KubeJS callback forms restore the previous value automatically and are safer for scoped modifiers. (heat_units is the example Java capability; the lookup throws without it.)

ServerEvents.recipes(event => {
  const heat = MBDRegistries.RECIPE_CAPABILITIES.get('heat_units')
  if (heat === null) throw new Error('heat_units capability is not registered')

  event.recipes.example.heat_press()
    .id('example:scoped_heat_press')
    .slotName('hot_side', r => r.inputs(heat, 500))
    .perTick(r => r.inputFE(20))
    .chance(0.25, r => r.outputItems('minecraft:diamond'))
})

Diagnosing “recipe never starts”

1. Confirm the capability exists in MBDRegistries.RECIPE_CAPABILITIES.
2. Confirm the machine has a trait returning a handler for that exact capability instance.
3. Confirm trait recipe handler IO supports the recipe direction.
4. If slotName is set, confirm the handler advertises it.
5. Simulate the requested amount against current storage and filters.
6. Check conditions separately; a handler shortage and condition failure are different errors.