Rigging characters — the full MCP tool loop

AETHER / 02 is the pinned default sample: an 18-bone humanoid with 11 clips, five materials, both UV sets, tangents and two material extensions. SkeletalMesh3D loads it and its hand.R is the weapon attachment bone. It is CC0, and was built from a 14-unit source robot, so its source size is preserved unless a game explicitly authors a SkeletalMesh3D.size override.

1. Inspect before deciding

asset_inspect_rig takes a local GLB path, or { "sourceId": "aether-02" } to acquire the pinned sample into the development cache, plus optional local UAL ZIP/GLB libraries. It reports meshes, joints, suggested bone-role mappings with ambiguity, attribute and extension support, measured bounds, clips, and the actual attachment candidates. It never downloads the animation libraries; supply local archives or select release donors by clip id.

2. Preserve or fit a rig

asset_auto_rig preserves an existing valid rig by default. For an unrigged upright biped it fits an 18-joint skeleton from measured geometry, then binds smooth (up to four normalized influences) or rigid (one bone per connected mechanical region) weights and publishes the skinned GLB under the project root. When the anatomy is ambiguous — arms joined to the torso, legs not separated — it returns a correction request with the measured landmarks instead of a bad rig; pass corrected overrides and call it again. Replacing a real rig requires replaceRig: true.

3. Select and retarget motion

asset_retarget_animations fetches only the donor clips you select from the pinned release and bakes them onto the target: { "id": "ual1/Walk_Loop", "variant": "in_place" }. In-place is the normal game-controlled locomotion output; root motion explicitly uses the matching root_motion variant. New clips keep their namespace (ual1/Walk_Loop) so an existing Walk is never overwritten. Existing target clips survive unless you pass keepExistingClips: false for a game-minimal export. Target materials, UVs, tangents and extensions are preserved.

4. Confirm with a contact sheet

asset_preview_animation renders a prepared GLB from two to six angles with an optional clip time or an explicit bone pose, and publishes a nonblank contact sheet under the project root. A missing rendering backend returns an explicit unavailable result; a blank frame fails. Inspect the sheet before delivery — a valid animation container alone is not approval.

5. Cook and play

Load the prepared GLB the ordinary way and play clips with SkeletalMesh3D and its update loop. Attach a game-authored weapon with attachToBone(character.root, "hand.R", weapon). Credit the source and keep its license notice with the asset; the donor libraries are CC0, and the pinned clips are fetched once into the development cache on first use, then reused offline.