CustomHitboxLib
by GawrMonster
CustomHitboxLib gives entities multipart hitboxes that go beyond the single square vanilla uses, and it is built for Forge and NeoForge.
What it does
Vanilla entities use one rectangular bounding box set by width and height. CustomHitboxLib lets an entity carry several sub-hitboxes, each with its own size and offset, so a boss can have collision on a head, a body and limbs. Part dimensions, offsets and behaviour are defined in JSON, and a developer can also attach sub-hitboxes at runtime through Forge Capabilities without editing the base entity class.
The library needs Code Required, and the environment is client and server, so servers and every player must run it. Files exist for 1.20.1 and 1.21.1: Forge 1.3.9 for 1.20.1 and NeoForge 2.0.9 for 1.21.1, both dated 2026-10-06. The code is open source under the MIT License, and public links for the source, issue tracker and wiki are listed.
Key features
Multipart hitboxes
An entity can carry several hitboxes, each with its own dimensions and offset, instead of one square.
JSON configuration
Part sizes, offsets and behaviours are set in JSON files, which also lets modpack creators reshape existing mobs.
Live reloading
Edits to custom hitboxes take effect in-game after a reload, so changes can be checked without restarting.
Damage forwarding
A hit on a custom sub-hitbox registers damage and directional knockback on the main entity.
Positioners and interpolation
Helper methods move parts relative to the entity, for example following behind it, with smooth interpolation between positions.
Compatibility
Latest build for each game version and loader.
Only full game releases are shown. This mod publishes no snapshot builds.
Use cases
Boss encounters
Bosses with a head, wings or limbs can take hits where each part is shaped to match the model.
Datapack tuning
Server owners can change the hitboxes of existing creatures through datapack files without a code change.
Who it’s for: Mod developers building bosses with precise collision use the API directly, with entities implementing its interfaces to control part lifecycles. Modpack creators and server owners can use the JSON files alone.
How it compares
More Hitboxes is open source under the MIT License, supports Fabric, Forge and NeoForge, and covers 1.18.2 – 1.21.1. HammerMultipart is for Forge and NeoForge across 1.20.1 – 1.21.1 and is not open source, with its license reserved to All rights reserved. CB Multipart is open source under the GNU Lesser General Public License v2.1 only and spans 1.5.2 – 1.21.1 on Forge and NeoForge.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| CustomHitboxLib | Forge and NeoForge | 1.20.1 – 1.21.1 | Client and server | 2026-10-06 |
| More Hitboxes | Fabric, Forge and NeoForge | 1.18.2 – 1.21.1 | Client and server | 2026-03-31 |
| HammerMultipart | Forge and NeoForge | 1.20.1 – 1.21.1 | Client and server | 2026-07-01 |
| CB Multipart | Forge and NeoForge | 1.5.2 – 1.21.1 | Client and server | 2026-03-30 |
Questions
Does CustomHitboxLib need to be installed on the server?
Which loaders and versions are supported?
Can a datapack change an existing mob's hitbox?
In the catalog
CustomHitboxLib is one of 3,514 Library mods on ModsFinder, and one of 1,576 Library mods for Forge. 32,366 mods support Minecraft 1.21.1.
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What the author says
CustomHitboxLib is a lightweight, powerful library mod for Forge 1.20.1 and NeoForge 1.21.1 that revolutionizes entity bounding boxes. It completely bypasses the limitations of Minecraft's hardcoded single, square-based hitboxes (width and height), introducing full multipart hitbox support for any entity—just like…
Official listing
- Modrinth page
- modrinth.com/mod/customhitboxlib
- Owner
- GawrMonster
- Published
- 2026-07-17
- Updated on Modrinth
- 2026-10-06
- Facts verified
- 2026-10-15