How do I install the Skeleton skill?

Run npx skillmds@latest add kevinpbuckley/skeleton in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

What does the Skeleton skill do?

Edit skeleton bone transforms/hierarchy, retargeting modes, curve metadata, blend profiles, bone constraints, and learn constraints from animations (VibeUE SkeletonService). Socket CRUD, bone enumeration, physics-asset, and material/LOD inspection are owned by the engine SkeletalMeshTools. Use when the user asks to add/transform bones, set retargeting, manage blend profiles or curves, or set bone constraints. For animation bone edits, also load animation-editing. It is listed under Coding & Dev Tools on SkillMD.

Is Skeleton safe to use?

This skill has not completed SkillMD's automated safety review yet. Independent scanners report: SkillSpector: PASS, Skill Scanner: PASS. Capability flags: docs only. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Skeleton?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Skeleton free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Skeleton?

kevinpbuckley (@kevinpbuckley) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Skeleton by kevinpbuckley — Agent Skill

Name: Skeleton
Rating: 4.2 (5 reviews)
Author: kevinpbuckley

🧠 Brains complement: IF an unreal-engine-skills-manager tool (external MCP) exists in this session, call it with {action: "load", skill: "animation-system"} for UE domain knowledge on this topic — correct APIs, architecture, best practices — and treat it as the rubric for any review / "best practices" question. If no such tool is available (e.g. running under Claude Code or Codex without that MCP), skip this line entirely and proceed with this skill alone — do NOT attempt the call.

Skeleton & Skeletal Mesh Skill

Architecture (read first): VibeUE extends Unreal's native MCP endpoint. Socket CRUD, bone enumeration, physics-asset assignment, and material/LOD/morph inspection are owned by the engine toolset editor_toolset.toolsets.skeletal_mesh.SkeletalMeshTools (called via call_tool). VibeUE's SkeletonService was trimmed to what the engine doesn't cover: bone transform/hierarchy editing, retargeting config, curve metadata, blend profiles, bone constraints, and learn-from-animations.

Loading skills: skills load through the engine's AgentSkillToolset (ListSkills/GetSkills) — there is no vibeue-skills-manager tool. Run VibeUE services with execute_python_code (unreal.SkeletonService.<method>()); reach engine tools with call_tool (discover with list_toolsets / describe_toolset).

Related Skills:

animsequence / animation-editing - For editing animations with constraint validation (uses skeleton profiles) and keyframes

animation-blueprint - For AnimBP state machines and navigation

Use this skill when: Editing bone transforms/hierarchy, retargeting modes, blend profiles, curve metadata, or bone constraints. For sockets / bone listing / physics asset / materials / LODs, use engine SkeletalMeshTools (see below).

Sockets, bone enumeration, inspection → engine SkeletalMeshTools

These moved to the engine. Discover the exact schemas with describe_toolset("editor_toolset.toolsets.skeletal_mesh.SkeletalMeshTools") and call via call_tool (the mesh argument is a {"refPath": "<SkeletalMesh asset path>"} object):

Task	Engine tool (`SkeletalMeshTools.*`)
List sockets	`get_socket_names`
Add / remove / rename socket	`add_socket`, `remove_socket`, `rename_socket`
Get / set socket transform, get socket bone	`get_socket_transform`, `set_socket_transform`, `get_socket_bone`
List bones / parent / children	`get_bone_names`, `get_bone_parent`, `get_bone_children`
Material slots / get / set	`get_material_slots`, `get_material`, `set_material`
Physics asset get / assign	`get_physics_asset`, `assign_physics_asset`
LODs / vertices / sections / bounds	`get_lod_count`, `get_vertex_count`, `get_section_count`, `get_bounds`
Morph target names	`get_morph_target_names`

# Example: add a socket on the hand_r bone, then list sockets
call_tool(toolset_name="editor_toolset.toolsets.skeletal_mesh.SkeletalMeshTools",
          tool_name="add_socket",
          arguments={"mesh": {"refPath": "/Game/Characters/SKM_Mannequin"},
                     "socket_name": "Weapon_R", "bone_name": "hand_r"})
call_tool(toolset_name="editor_toolset.toolsets.skeletal_mesh.SkeletalMeshTools",
          tool_name="set_socket_transform",
          arguments={"mesh": {"refPath": "/Game/Characters/SKM_Mannequin"},
                     "socket_name": "Weapon_R",
                     "transform": {"location": {"x":10,"y":0,"z":0},
                                   "rotation": {"pitch":0,"yaw":90,"roll":0},
                                   "scale": {"x":1,"y":1,"z":1}}})

Note: the engine add_socket always adds the socket to the skeletal mesh. VibeUE's old bAddToSkeleton (skeleton-wide socket) flag is gone — to share a socket across all meshes on a skeleton, add it on each mesh, or add it on the skeleton via unreal.* directly.

Critical Rules

⚠️ Bone Modification Requires Commit

Bone modifications (add, remove, rename, reparent) use a transaction system. Changes are NOT applied until you call commit_bone_changes():

import unreal

# Make bone changes
unreal.SkeletonService.add_bone("/Game/SKM_Character", "twist_arm_l", "upperarm_l", unreal.Transform())
unreal.SkeletonService.add_bone("/Game/SKM_Character", "twist_arm_r", "upperarm_r", unreal.Transform())

# ⚠️ CRITICAL: Commit changes!
unreal.SkeletonService.commit_bone_changes("/Game/SKM_Character")

Forgetting to commit = changes are lost!

⚠️ Do NOT reparent bones via SkeletonModifier (known-broken, UE 5.7). Changing a bone's parent and calling commit_bone_changes() fails with a hierarchy-mismatch validation error and can leave the commit stalled (the call may not return cleanly). Add/remove/rename/transform are safe; reparenting is not. If a user needs a different hierarchy, add a new bone at the desired parent and remove the old one rather than reparenting in place.

Sockets are now an engine operation

Socket CRUD is on SkeletalMeshTools (see the table at the top). The engine add_socket attaches to the skeletal mesh; set its offset with set_socket_transform. There is no bAddToSkeleton flag.

Skeleton vs SkeletalMesh Paths

Skeleton operations (retargeting, curves, blend profiles, constraints) use SK_ assets → VibeUE SkeletonService
SkeletalMesh bone transform/hierarchy edits use SKM_ assets → VibeUE SkeletonService
SkeletalMesh sockets / bone listing / inspection use SKM_ assets → engine SkeletalMeshTools

# Skeleton operations (VibeUE) - use SK_ path
unreal.SkeletonService.get_skeleton_info("/Game/Characters/SK_Mannequin")
unreal.SkeletonService.set_bone_retargeting_mode("/Game/Characters/SK_Mannequin", "pelvis", "Skeleton")

# Sockets / bone listing (engine) - use SKM_ path via call_tool, e.g.:
# call_tool("editor_toolset.toolsets.skeletal_mesh.SkeletalMeshTools", "get_socket_names",
#           {"mesh": {"refPath": "/Game/Characters/SKM_Mannequin"}})

Retargeting Mode Reference

Mode	Description	Use For
`Animation`	Use animation data directly	Most bones (default)
`Skeleton`	Use skeleton's reference pose	Root, pelvis, IK targets
`AnimationScaled`	Scale animation by skeleton size	Height-scaled characters
`OrientAndScale`	Match orientation and scale	Helper/utility bones

Skeleton Profiles & Constraints

For animation editing with constraint validation, use the skeleton profile methods:

import unreal

# Create/refresh skeleton profile with hierarchy and constraints
profile = unreal.SkeletonService.create_skeleton_profile("/Game/SK_Mannequin")
print(f"Skeleton has {profile.bone_count} bones")

# Learn constraints from existing animations
constraints = unreal.SkeletonService.learn_from_animations("/Game/SK_Mannequin", 50, 10)
print(f"Learned from {constraints.animation_count} animations")

# Set manual bone constraints (e.g., elbow as hinge)
unreal.SkeletonService.set_bone_constraints(
    "/Game/SK_Mannequin",
    "lowerarm_r",
    unreal.Rotator(0, 0, 0),     # Min rotation
    unreal.Rotator(0, 145, 0),   # Max rotation
    True,  # Is hinge joint
    1      # Pitch axis (Y)
)

# Validate a rotation against constraints
result = unreal.SkeletonService.validate_bone_rotation(
    "/Game/SK_Mannequin",
    "upperarm_r",
    unreal.Rotator(0, 180, 0),  # Test rotation
    True  # Use learned constraints
)
if not result.is_valid:
    print(f"Clamped to: {result.clamped_rotation}")

See the animsequence skill for complete preview→validate→bake workflow.

Workflows

List All Bones (engine SkeletalMeshTools)

Bone enumeration moved to the engine. Use get_bone_names (hierarchy order, root first) and walk parent/children with get_bone_parent / get_bone_children:

# names = call_tool("editor_toolset.toolsets.skeletal_mesh.SkeletalMeshTools",
#                   "get_bone_names", {"mesh": {"refPath": "/Game/Characters/SKM_Mannequin"}})
# for n in names:
#     children = call_tool(... "get_bone_children",
#                          {"mesh": {"refPath": "/Game/Characters/SKM_Mannequin"}, "bone_name": n})

For a richer hierarchy with transforms/depth/retarget mode, VibeUE's create_skeleton_profile(skeleton_path) returns bone_hierarchy (Array[BoneNodeInfo]) — see below.

Add Twist Bones for Better Skinning

import unreal

mesh_path = "/Game/Characters/SKM_Character"

# Add forearm twist bones
unreal.SkeletonService.add_bone(
    mesh_path,
    "lowerarm_twist_01_l",
    "lowerarm_l",
    unreal.Transform(location=[12.0, 0.0, 0.0])
)

unreal.SkeletonService.add_bone(
    mesh_path,
    "lowerarm_twist_01_r",
    "lowerarm_r",
    unreal.Transform(location=[12.0, 0.0, 0.0])
)

# Add upperarm twist bones
unreal.SkeletonService.add_bone(
    mesh_path,
    "upperarm_twist_01_l",
    "upperarm_l",
    unreal.Transform(location=[15.0, 0.0, 0.0])
)

unreal.SkeletonService.add_bone(
    mesh_path,
    "upperarm_twist_01_r",
    "upperarm_r",
    unreal.Transform(location=[15.0, 0.0, 0.0])
)

# CRITICAL: Commit the changes
unreal.SkeletonService.commit_bone_changes(mesh_path)
unreal.SkeletonService.save_asset(mesh_path)

Set Up Weapon Sockets (engine SkeletalMeshTools)

Socket CRUD is on the engine toolset. Add the socket, then set its offset transform:

mesh = {"refPath": "/Game/Characters/SKM_Character"}
TS = "editor_toolset.toolsets.skeletal_mesh.SkeletalMeshTools"

call_tool(TS, "add_socket", {"mesh": mesh, "socket_name": "Weapon_R", "bone_name": "hand_r"})
call_tool(TS, "set_socket_transform", {"mesh": mesh, "socket_name": "Weapon_R",
          "transform": {"location": {"x":10,"y":0,"z":0},
                        "rotation": {"pitch":0,"yaw":90,"roll":0},
                        "scale": {"x":1,"y":1,"z":1}}})

call_tool(TS, "add_socket", {"mesh": mesh, "socket_name": "Holster_Back", "bone_name": "spine_03"})
call_tool(TS, "set_socket_transform", {"mesh": mesh, "socket_name": "Holster_Back",
          "transform": {"location": {"x":0,"y":-20,"z":0},
                        "rotation": {"pitch":0,"yaw":0,"roll":90},
                        "scale": {"x":1,"y":1,"z":1}}})

Configure Retargeting for Animation Sharing

import unreal

skeleton_path = "/Game/Characters/SK_Character"

# Root and pelvis should use Skeleton mode
for bone in ["root", "pelvis"]:
    unreal.SkeletonService.set_bone_retargeting_mode(skeleton_path, bone, "Skeleton")

# IK bones should use Animation mode
for bone in ["ik_foot_l", "ik_foot_r", "ik_hand_l", "ik_hand_r"]:
    unreal.SkeletonService.set_bone_retargeting_mode(skeleton_path, bone, "Animation")

# Add a compatible skeleton for sharing animations
unreal.SkeletonService.add_compatible_skeleton(
    skeleton_path,
    "/Game/Mannequins/SK_Mannequin"
)

unreal.SkeletonService.save_asset(skeleton_path)

Create Upper Body Blend Profile

import unreal

skeleton_path = "/Game/Characters/SK_Character"

# Create the blend profile
unreal.SkeletonService.create_blend_profile(skeleton_path, "UpperBody")

# Set lower body to 0 (no blend)
lower_body_bones = ["pelvis", "thigh_l", "thigh_r", "calf_l", "calf_r", "foot_l", "foot_r"]
for bone in lower_body_bones:
    unreal.SkeletonService.set_blend_profile_bone(skeleton_path, "UpperBody", bone, 0.0)

# Set upper body to 1 (full blend)
upper_body_bones = ["spine_01", "spine_02", "spine_03", "clavicle_l", "clavicle_r"]
for bone in upper_body_bones:
    unreal.SkeletonService.set_blend_profile_bone(skeleton_path, "UpperBody", bone, 1.0)

unreal.SkeletonService.save_asset(skeleton_path)

Set Up Morph Target Curves

import unreal

skeleton_path = "/Game/Characters/SK_Character"

# Add facial expression curves
facial_curves = ["BrowsUp", "BrowsDown", "EyesClosed", "Smile", "Frown"]
for curve in facial_curves:
    unreal.SkeletonService.add_curve_metadata(skeleton_path, curve)
    unreal.SkeletonService.set_curve_morph_target(skeleton_path, curve, True)

# Add material parameter curves
material_curves = ["EyeGlow", "SkinWetness", "BlushAmount"]
for curve in material_curves:
    unreal.SkeletonService.add_curve_metadata(skeleton_path, curve)
    unreal.SkeletonService.set_curve_material(skeleton_path, curve, True)

unreal.SkeletonService.save_asset(skeleton_path)

Find Bones by Pattern (filter engine bone list)

There is no find_bones — get the full list from the engine get_bone_names and filter in Python:

names = call_tool("editor_toolset.toolsets.skeletal_mesh.SkeletalMeshTools",
                  "get_bone_names", {"mesh": {"refPath": "/Game/Characters/SKM_Mannequin"}})
hand_bones  = [n for n in names if "hand"  in n.lower()]
twist_bones = [n for n in names if "twist" in n.lower()]
ik_bones    = [n for n in names if n.lower().startswith("ik_")]

Get Full Skeleton Info

import unreal

skeleton_path = "/Game/Characters/SK_Mannequin"

info = unreal.SkeletonService.get_skeleton_info(skeleton_path)
print(f"Skeleton: {info.skeleton_name}")
print(f"  Bones: {info.bone_count}")
print(f"  Compatible Skeletons: {info.compatible_skeleton_count}")
print(f"  Curve Metadata: {info.curve_meta_data_count}")
print(f"  Blend Profiles: {info.blend_profile_count}")
if info.blend_profile_names:
    print(f"    Profiles: {', '.join(info.blend_profile_names)}")

Data Structures

Python Naming Convention: C++ types like FBoneNodeInfo are exposed as BoneNodeInfo in Python (no F prefix).

BoneNodeInfo

Property	Type	Description
`bone_name`	string	Name of the bone
`bone_index`	int	Index in hierarchy
`parent_bone_name`	string	Parent bone (empty = root)
`parent_bone_index`	int	Parent index (-1 = root)
`child_count`	int	Number of direct children
`depth`	int	Depth in hierarchy (0 = root)
`local_transform`	Transform	Transform relative to parent
`global_transform`	Transform	World-space transform
`retargeting_mode`	string	Translation retarget mode
`children`	array[string]	Names of child bones

SkeletonAssetInfo

Property	Type	Description
`skeleton_path`	string	Asset path
`skeleton_name`	string	Display name
`bone_count`	int	Number of bones
`compatible_skeleton_count`	int	Compatible skeletons
`curve_meta_data_count`	int	Curve metadata entries
`blend_profile_count`	int	Blend profiles
`blend_profile_names`	array[string]	Profile names
`preview_forward_axis`	string	Forward axis setting

SkeletalMeshData

Property	Type	Description
`mesh_path`	string	Asset path
`mesh_name`	string	Display name
`skeleton_path`	string	Associated skeleton
`bone_count`	int	Number of bones
`lod_count`	int	LOD levels
`socket_count`	int	Number of sockets
`morph_target_count`	int	Morph targets
`material_count`	int	Materials
`physics_asset_path`	string	Physics asset
`post_process_anim_bp_path`	string	Post-process AnimBP

Common Mistakes

❌ WRONG: Forgetting to commit bone changes

unreal.SkeletonService.add_bone(path, "new_bone", "parent", transform)
# Bone is NOT added yet - changes lost!

✅ RIGHT: Always commit bone changes

unreal.SkeletonService.add_bone(path, "new_bone", "parent", transform)
unreal.SkeletonService.commit_bone_changes(path)  # NOW it's applied

❌ WRONG: Calling `unreal.SkeletonService.add_socket(...)`

That method was cut — sockets are now engine SkeletalMeshTools:

# WRONG: unreal.SkeletonService.add_socket(...)               # no longer exists
# RIGHT: call_tool("editor_toolset.toolsets.skeletal_mesh.SkeletalMeshTools",
#                  "add_socket", {"mesh": {"refPath": "/Game/SKM_Character"}, ...})

❌ WRONG: Not saving after VibeUE modifications

unreal.SkeletonService.set_bone_retargeting_mode(path, "pelvis", "Skeleton")
# Changes in memory only - lost on editor close!

✅ RIGHT: Save after modifications

unreal.SkeletonService.set_bone_retargeting_mode(path, "pelvis", "Skeleton")
unreal.SkeletonService.save_asset(path)

Engine SkeletalMeshTools (via call_tool) — sockets, bone enumeration, physics asset, materials, LODs, morph targets.
animation-editing / animsequence — bone-rotation editing on animations using skeleton profiles.

Skeleton

File contents

Skeleton & Skeletal Mesh Skill

Sockets, bone enumeration, inspection → engine SkeletalMeshTools

Critical Rules

⚠️ Bone Modification Requires Commit

Sockets are now an engine operation

Skeleton vs SkeletalMesh Paths

Retargeting Mode Reference

Skeleton Profiles & Constraints

Workflows

List All Bones (engine SkeletalMeshTools)

Add Twist Bones for Better Skinning

Set Up Weapon Sockets (engine SkeletalMeshTools)

Configure Retargeting for Animation Sharing

Create Upper Body Blend Profile

Set Up Morph Target Curves

Find Bones by Pattern (filter engine bone list)

Get Full Skeleton Info

Data Structures

BoneNodeInfo

SkeletonAssetInfo

SkeletalMeshData

Common Mistakes

❌ WRONG: Forgetting to commit bone changes

✅ RIGHT: Always commit bone changes

❌ WRONG: Calling `unreal.SkeletonService.add_socket(...)`

❌ WRONG: Not saving after VibeUE modifications

✅ RIGHT: Save after modifications

Related

Frequently asked questions

Skeleton

File contents

Skeleton & Skeletal Mesh Skill

Sockets, bone enumeration, inspection → engine SkeletalMeshTools

Critical Rules

⚠️ Bone Modification Requires Commit

Sockets are now an engine operation

Skeleton vs SkeletalMesh Paths

Retargeting Mode Reference

Skeleton Profiles & Constraints

Workflows

List All Bones (engine SkeletalMeshTools)

Add Twist Bones for Better Skinning

Set Up Weapon Sockets (engine SkeletalMeshTools)

Configure Retargeting for Animation Sharing

Create Upper Body Blend Profile

Set Up Morph Target Curves

Find Bones by Pattern (filter engine bone list)

Get Full Skeleton Info

Data Structures

BoneNodeInfo

SkeletonAssetInfo

SkeletalMeshData

Common Mistakes

❌ WRONG: Forgetting to commit bone changes

✅ RIGHT: Always commit bone changes

❌ WRONG: Calling unreal.SkeletonService.add_socket(...)

❌ WRONG: Not saving after VibeUE modifications

✅ RIGHT: Save after modifications

Related

Related skills

Frequently asked questions

How do I install the Skeleton skill?

What does the Skeleton skill do?

Is Skeleton safe to use?

Which AI agents work with Skeleton?

Is Skeleton free to use?

Who published Skeleton?

❌ WRONG: Calling `unreal.SkeletonService.add_socket(...)`