Machine and Recipe-Type Events

Current API Minecraft 1.21.1 / MBD2 21.1.1

MBD2 event subscriptions are targeted. The first argument is the exact machine-definition or recipe-type ID; the callback receives a KubeJS wrapper whose Java event is wrapper.event.

// kubejs/server_scripts/mbd2_events.js
MBDMachineEvents.onAfterRecipeWorking('example:crusher', wrapper => {
  const event = wrapper.event
  console.info(`Recipe ${event.recipe.id} left its active run at ${event.machine.pos}`)
})

Do not target a block ID or a recipe ID. A machine handler targets an ID in MBDRegistries.MACHINE_DEFINITIONS; a recipe-type handler targets an ID in MBDRegistries.RECIPE_TYPES.

Blueprints cover the same events

Every event on this page is also a blueprint entry node, so the same reaction can be drawn in the editor instead of scripted. Choose KubeJS when the pack already scripts; choose a blueprint when the machine should ship self-contained.

Server machine events

All of these live in kubejs/server_scripts. wrapper.event.machine is always present.

Handler	Extra fields	Cancellable	When it runs
onLoad	—	no	One tick after the block entity becomes valid
onRemoved	—	no	The machine is being removed
onPlaced	player, itemStack	no	Placed by an entity
onNeighborChanged	block, fromPos	no	A neighbour update reached the machine
onDrops	entity, mutable drops	no	Drop list assembled, before it is spawned
onOpenUI	player	yes	Before the machine UI opens
onUseWithoutItem	player, hit, mutable interactionResult	no	Empty-hand right click
onUseCatalyst	catalyst, player, hand	yes	Multiblock catalyst use
onUI	mutable ui, mutable player	no	The server built the machine UI
onStateChanged	oldState, newState	yes	A machine-state transition
onStructureFormed / onStructureInvalid	—	no	Multiblock formation and loss
onTick	—	yes	Before recipe logic and every trait tick

drops is the live Java List<ItemStack>; add to it rather than replacing it. Cancelling onTick skips recipe logic and every trait's serverTick.

Recipe lifecycle events

Handler	Extra fields	Cancellable	Exact point
onBeforeRecipeModify	mutable recipe	yes	Before configured modifiers and parallel calculation
onAfterRecipeModify	mutable recipe	no	After modifiers produced the effective recipe
onBeforeRecipeWorking	recipe	yes	After fuel is taken, before inputs are committed
onRecipeWorking	recipe, progress	yes	After this tick's per-tick IO committed, before progress increments
onRecipeWaiting	recipe	no	Status became WAITING
onAfterRecipeWorking	recipe	no	Completion or interruption, before outputs
onConsumeInputsAfterWorking	recipe	no	Deferred inputs were committed at completion
onRecipeFinish	recipe	no	After the outputs exist
onFuelRecipeModify	mutable recipe	yes	A fuel candidate matched, before its inputs are taken
onFuelBurningFinish	nullable recipe	no	Registered, but not delivered — see below

onAfterRecipeWorking fires before outputs are produced; onRecipeFinish fires after. Use the latter for "a craft completed" bonuses, or a bonus item lands in the slot the recipe's own output still needs.

onConsumeInputsAfterWorking only fires when the machine's Consume inputs after working setting is on — as a definition value, or as a per-machine runtime value override of recipe_logic.consume_inputs_after_working.

onFuelBurningFinish never fires

MBDMachine#onFuelBurningFinish posts its event to the NeoForge bus without postCustomEvent(), so neither the KubeJS handler nor the blueprint entry node receives it in 21.1.1. Java NeoForge.EVENT_BUS listeners do work. Track fuel exhaustion through onRecipeWaiting or machine.recipeLogic.fuelTime instead.

An event with no KubeJS handler

MachineUseItemOnEvent (right click with an item) exists and has a blueprint entry node, but MBDServerEvents registers no KubeJS name for it. Use a blueprint, or a Java listener on NeoForge.EVENT_BUS.

MBDMachineEvents.onRecipeWorking('example:crusher', wrapper => {
  const { recipe, progress } = wrapper.event
  if (progress % 20 === 0) {
    console.debug(`${recipe.id}: ${progress}/${recipe.duration}`)
  }
})

Cancelling

Two equivalent forms, for the handlers marked cancellable above:

MBDMachineEvents.onOpenUI('example:crusher', wrapper => {
  wrapper.event.setCanceled(true)          // set it on the Java event
})

MBDMachineEvents.onOpenUI('example:crusher', wrapper => {
  return false                             // KubeJS interrupt-false, mapped to setCanceled
})

Cancelling is a control-flow decision, not a substitute for recipe conditions — a cancelled onBeforeRecipeWorking runs after fuel was already consumed, and a cancelled onRecipeWorking runs after that tick's per-tick IO committed. Put eligibility in a RecipeCondition.

Never move resources in an event that can run during simulation or on the client. Resource accounting belongs in a Java IRecipeHandlerTrait.

Client events

These belong in kubejs/client_scripts.

Handler	Group	Fields
onClientTick(machineId, cb)	MBDMachineEvents	machine
onCustomDataUpdate(machineId, cb)	MBDMachineEvents	oldValue, newValue; cancellable
onCustomKeyframe(machineId, cb)	MBDMachineEvents	instruction, controllerName, animationTick; GeckoLib only
onRecipeUI(recipeTypeId, cb)	MBDRecipeTypeEvents	mutable recipe, mutable ui; cancellable
registerCustomRenderers(cb)	MBDClientEvents	not targeted — see script renderers

// kubejs/client_scripts/mbd2_visuals.js
MBDMachineEvents.onCustomDataUpdate('example:crusher', wrapper => {
  const { oldValue, newValue } = wrapper.event
  console.debug(`Client machine data changed: ${oldValue} -> ${newValue}`)
})

Keep these visual-only. Holding a machine object on the client does not transfer server authority.

Proxy-recipe transfer

// kubejs/server_scripts/mbd2_proxy.js
MBDRecipeTypeEvents.onTransferProxyRecipe('example:electric_furnace', wrapper => {
  const event = wrapper.event
  // event.recipeType       target MBDRecipeType
  // event.proxyTypeId      source vanilla/mod recipe type ID
  // event.proxyType        source RecipeType object
  // event.proxyRecipeId    source recipe ID
  // event.proxyRecipe      source recipe object
  // event.mbdRecipe        nullable, mutable converted result
  if (`${event.proxyTypeId}` !== 'minecraft:smelting') {
    event.setCanceled(true)
  }
})

This filters recipes produced by a proxy the recipe type already declares; it does not enable one. See proxy recipe types.

Tick cost

onTick, onClientTick, and onRecipeWorking run every tick per machine. Do not scan the world, parse IDs, rebuild collections, or allocate UI objects in them.