Hitbox

A hitbox defines the physical "boundaries" (or an approximation thereof) of a block or entity. Hitboxes are utilised in the calculations of collisions and targeting.

Unlike with block models, all hitboxes are hardcoded and cannot be changed without modification, even via data packs.

Collision box
Collision box is used to manage collision with entities.

Collision box is not present for all blocks, as all non-solid blocks such as grass, signs, button, lever and torch have no collision box.

Outline box
Outline box is shown when looking at a given block. It becomes visible as a wireframe outline when the crosshairs are pointed at the block.

Interaction box
Interaction box deals with aiming at blocks. When the interaction box of a block is targeted, the block can be broken, placed on or interacted with as necessary.

Its default is the same as the outline box. There are some exceptions:

Another major difference is that the interaction box is incapable of extending outside of its own block space, despite the outline box being capable of doing so visually. There are several instances where this can be seen:


 * The arm of an extended piston - specifically the part which protrudes into the piston's block space.
 * The hitboxes of pointed dripstone in Java Edition 20w48a could sometimes also randomly extend into adjacent blocks, allowing this to be seen.
 * The hitboxes of melon stems and pumpkin stems with ages 8 and over could visually extend into the block space above them while they existed (from Beta 1.8 Pre-release up to the removal of the last four in 14w10a and the remaining four in 14w25a).
 * The hitboxes of cakes with 8 or more bites could extend into the adjacent block space while these existed (from Beta 1.2 up to their removal in 14w26a, although 14w25a likely made them too unstable to be properly observable)
 * The hitboxes of cakes and cacti at far distances could previously (from Beta 1.2 and Alpha v1.0.11 respectively up to their fixing, likely simultaneously in 15w49a, although it became unobservable for cake from 15w38a onwards due to ) also become greater than a full block, allowing this to be seen.

Block support shape
Block support shape is mainly used to judge whether another attaching block (e.g. torches, doors, buttons, etc.) can be attached to it.

Its default is the same as the collision box. There are some exceptions:
 * Leaves have an empty block support shape.
 * The Block support shape of the snow layer is the same as its selection box.
 * Soul sand has a full block support shape.

Entity
The hitboxes of most entities (except ender dragon) are always shaped in cuboids, which does not always overlap with the visual parameters of the entity. For example, the witch's hitbox does not include the top section of its hat, and the wither's hitbox does not include the two heads on its sides.

Boundary box
The boundary box of entities can be viewed via the +  debug shortcut.

Interaction box
Interaction box deals with aiming at entities. When the interaction box of an entity is targeted, the entity can be hit or interacted with as necessary.

Headspace
The headspace is outlined in red, and appears only on the hitboxes of mobs. It is outlined in red, and it is responsible for suffocation and drowning damage. If a block that causes suffocation is pushed into the headspace, then the entity takes suffocation damage. If the headspace is in water, then the entity's breath bar goes down, and then the entity drowns.

Trivia

 * Fluids do not have hitboxes, even in cases where they would behave like a block.
 * The ender dragon is composed of nine distinct hitboxes.