Dispensers & Droppers ​

Dispenser and dropper blocks carry a real block-entity inventory. Fill one, trigger it, and it pops an item in the direction it faces — launching arrows, snowballs, eggs, and ender pearls as projectiles, and ejecting everything else as a dropped item. Every fire passes through the cancellable Block.on_dispense method, and a script can fire one directly with dispense from.

command "dispense-demo" {
    execute {
        dispense from location(0.0, 64.0, 0.0)
        send "<gray>Fired the dispenser at 0, 64, 0." to sender
    }
}

Block-entity inventories ​

A placed dispenser or dropper owns a 3×3 inventory. Right-clicking the block opens it, and its contents live for as long as the block does — kept per block, keyed by world position. Breaking the block drops its remaining contents into the world and clears the store. There is nothing to declare: the inventory exists the moment the block is placed.

How a dispenser fires ​

A dispenser or dropper activates three ways:

When it fires, the block pops one item, advancing through its slots round-robin just like vanilla. Droppers always eject the item as a dropped entity. Dispensers inspect the item first: arrows, snowballs, eggs, and ender pearls launch as projectiles along the block's facing direction; everything else ejects as a dropped item with the usual spread.

dispense from ​

dispense from <location> fires the dispenser or dropper at that block position from a script — the third activation path, and the one you reach for in commands and events:

dispense from location(10.0, 65.0, 10.0)

The expression must be a Location; if the block there is not a dispenser or dropper, the statement is a no-op at that position (nothing to fire).

The Block.on_dispense method ​

Every fire — lever, redstone, or dispense from — calls the Block receiver's on_dispense method before the item moves, so a handler can watch it, swap what comes out, or stop it entirely. block is the dispenser block (its type is block.id), and the method is cancellable.

Block {
    on_dispense {
        send "<gray>A dispenser fired, facing ${direction}." to all players
    }
}

Because item is read-write, you can substitute the payload:

Block {
    on_dispense {
        if item.material is "minecraft:arrow" {
            // turn every dispensed arrow into a snowball
            set item to item("SNOWBALL")
        }
    }
}

Cancel to jam the block — nothing leaves it:

Block {
    on_dispense {
        if block.id is "minecraft:dropper" {
            cancel event
        }
    }
}