Applying Status Effects from Custom Blocks

In older versions of the Bedrock add-on format, blocks could run slash commands or apply effects directly inside the block JSON using event responses like add_mob_effect under the Holiday Creator Features toggle. Those JSON event responses were removed when Holiday Creator Features was retired.

Today, applying a status effect from a block requires two parts: a behavior pack block file that declares a custom component identifier, and a TypeScript or JavaScript file registered through the @minecraft/server module. When a game event happens on the block, Bedrock fires the matching handler in your script, which then calls the addEffect method on the target entity.

Your block definition needs the minecraft:custom_components list inside its components object. Every string in this list must match a component name you register during the worldInitialize or system.beforeEvents.startup phase in your script.

If you want the effect to trigger when an entity walks onto the block, the block must have a collision box that entities can actually touch. A full cube has this by default, while a carpet-like block needs a thin minecraft:collision_box so the step-on event still registers.

{
  "format_version": "1.21.10",
  "minecraft:block": {
    "description": {
      "identifier": "wiki:healing_pad",
      "menu_category": {
        "category": "construction"
      }
    },
    "components": {
      "minecraft:collision_box": {
        "origin": [-8, 0, -8],
        "size": [16, 2, 16]
      },
      "minecraft:selection_box": {
        "origin": [-8, 0, -8],
        "size": [16, 2, 16]
      },
      "minecraft:geometry": "minecraft:geometry.full_block",
      "minecraft:destructible_by_mining": {
        "seconds_to_destroy": 1.5
      },
      "minecraft:custom_components": [
        "wiki:apply_regeneration"
      ]
    }
  }
}

Inside your script entry file, register the custom component inside system.beforeEvents.startup (or worldInitialize in slightly older script versions). The BlockCustomComponent interface gives you several hooks: onStepOn fires the moment an entity's feet land on top of the block, and onPlayerInteract fires when a player right-clicks or taps the block.

Both event objects give you direct access to the entity or player involved. Call entity.addEffect(effectType, durationInTicks, options) to grant the status effect. Remember that 20 ticks equal one second of real time, and the amplifier is zero-indexed (an amplifier of 0 gives Level I, while 1 gives Level II).

import { system } from "@minecraft/server";

system.beforeEvents.startup.subscribe((initEvent) => {
  initEvent.blockComponentRegistry.registerCustomComponent(
    "wiki:apply_regeneration",
    {
      onStepOn(event) {
        const entity = event.entity;
        if (!entity) return;

        entity.addEffect("regeneration", 100, {
          amplifier: 1,
          showParticles: true
        });
      },
      onPlayerInteract(event) {
        const player = event.player;
        if (!player) return;

        player.addEffect("absorption", 600, {
          amplifier: 0,
          showParticles: false
        });
      }
    }
  );
});

onStepOn only triggers once when an entity first walks onto the block. If a player stands completely still on the block, onStepOn will not fire again until they leave and step back on. To keep an effect active for as long as someone stands on or near the block, pair your custom component with minecraft:tick in the block JSON.

Add minecraft:tick to your block's components and set an interval_range in ticks, such as [20, 20] to run once per second. Then implement the onTick handler in your custom component. Inside onTick, use event.dimension.getEntities to search a small radius around event.block.location and apply the effect to every matching entity found.

import { system } from "@minecraft/server";

system.beforeEvents.startup.subscribe((initEvent) => {
  initEvent.blockComponentRegistry.registerCustomComponent(
    "wiki:poison_aura",
    {
      onTick(event) {
        const { block, dimension } = event;
        const center = block.center();

        const targets = dimension.getEntities({
          location: center,
          maxDistance: 4
        });

        for (const target of targets) {
          target.addEffect("poison", 60, {
            amplifier: 0,
            showParticles: true
          });
        }
      }
    }
  );
});

When calling addEffect on an Entity or Player object in @minecraft/server, the arguments control how long the effect lasts and how visible it is to the player.

Note that certain instantaneous effects like instant_health or instant_damage still require a duration of at least 1 tick to process properly, even though their impact happens on the first tick.

Applies to Minecraft Bedrock 1.21.0 and newer using stable format_version and @minecraft/server 1.11.0+. No experimental toggles are required for custom block components or addEffect in current releases.

Read out of the game itself, so the ids match the version you are building for.