Testing a species

Quick loop

/reload                              picks up data/ changes
F3 + T                               picks up assets/ changes
/ancientcreature species list        confirm it loaded
/ancientcreature summon mypack:stegosaurus

Editing a species and running /reload updates attributes, size and AI on creatures already in the world — no need to kill and respawn.

Checklist

Check	How
It loads	/ancientcreature species list shows the id
Behaviour resolved as intended	/ancientcreature species get <id> lists the final component set
Hitbox matches physical	F3 + B and look at the box
It renders	If invisible, the log names the missing geometry or texture
Animations play	Walk it around, hit it, watch state changes
Size and growth	Spawn a baby with {Age:-24000} and compare
Survives a restart	Save, quit, reload — species and variant persist
Sounds	Ambient, hurt, death, step, attack
Breeding	Feed two adults; an egg is laid and hatches the same species
Hunting	/ancientcreature hunger <targets> 0, then watch it pick a target
Identification GUI	Open the Fossil Identification Chamber — it should be listed and framed
Full progression	Fossil → DNA → genome → embryo → egg → capsule

Hunger in Jade

Hunger decides whether a predator attacks, and it is otherwise invisible. If Jade is installed, looking at a creature shows it:

Tyrannosaurus Rex
Hunger: 14/20
Fed - not hunting

The second line only appears once the value has crossed a threshold — red Hungry - will hunt at or below hunt_threshold, green Fed - not hunting at or above full_threshold. In the gap between them the creature is in the middle of the band, still finishing whatever hunt it started.

Toggle the readout under Jade's own settings, as Creature Hunger.

The value comes straight from synchronised entity data, so it is live and needs no server round-trip. It does not appear until the species' datapack is loaded, because until then the creature is running on fallback values rather than its own.

Without Jade, /ancientcreature hunger reports the same thing and can also set it.

Deliberate breakage

Worth doing once so you recognise the messages:

Disable the datapack, keep the resource pack, /reload. The creature goes inert — no AI, default size — and logs:

No species definition for 'mypack:stegosaurus'. Creatures of this species will stay inert with
default size and attributes until the datapack providing it is loaded.

Re-enable and /reload: it recovers. The species id is never rewritten, so nothing is lost.

Break the JSON. Put "width": 0 in and /reload. The file is named, the reason given, the species skipped — and every other species still loads.

Rename a bone in the geometry but not the animation. The animation still plays; the renamed channel is dropped with a warning naming the animation and the bone.

Common problems

Symptom	Likely cause
Not in species list	Datapack half missing, or the file failed to parse — check the log
Listed but invisible	No client entity with the species id as its identifier, or a wrong geometry or texture in it; the log says which
Renders but in T-pose	No controller in scripts.animate, or its states play animations missing from the client entity's animations map
Saddle or armor doesn't show	The client entity has no render controller drawing the gear layers; see render controllers
Texture scrambled	texture_width/texture_height in the geometry don't match the PNG
Hitbox wrong size	physical in the datapack, not render_scale in the resource pack
Too big/small in the GUI	Tune gui.scale in the species settings file
Ignores you entirely	No behaviour components, the ones chosen do not target players, or the creature is simply fed — check /ancientcreature hunger
Dies on land	An aquatic species breathes water by default and dries out on land; give it water, or set respiration
Flying creature walks	entity_category is not "flying", so the flight components skip themselves

Automated tests

The mod's own tests parse every shipped species, client entity, render controller, geometry, animation and controller through the real loaders, check the geometry baker against vanilla models and Blockbench's UV rules, and exercise Molang, animation sampling and genetics:

./gradlew :common:test

They also check that a broken definition is rejected — so if you are contributing a species to the mod itself, adding it there gets you the same coverage.