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SKILL.md
npx skills add vladmdgolam/agent-skills --skill blender-mcp
Blender MCP expert for scene inspection, Python scripting, GLTF export, and material/animation extraction. Activate when: (1) using Blender MCP tools (get_scene_info, execute_python, screenshot, etc.), (2) writing Blender Python scripts for extraction or manipulation, (3) exporting scenes to GLTF/GLB for web (Three.js, R3F), (4) debugging material or texture export losses, (5) optimizing GLB files with gltf-transform, (6) using asset integrations (PolyHaven, Sketchfab, Hyper3D Rodin, Hunyuan3D). Covers critical export gotchas, material mapping survival, texture optimization pipeline, headless CLI patterns, and known failure modes.
npx skills add vladmdgolam/agent-skills --skill blender-mcp
Use structured MCP tools (get_scene_info, screenshot) for quick inspection.
Use execute_python for anything non-trivial: hierarchy traversal, material extraction, animation baking, bulk operations. It gives full bpy API access and avoids tool schema limitations.
Use headless CLI for GLTF exports — the MCP server times out on export operations.
get_scene_info — verify connection (default port 9876)execute_python with print("ok") — verify Python worksscreenshot — verify viewport capture worksIf MCP is unresponsive, check that the Blender MCP addon is enabled and the socket server is running.
This is the end-to-end linear narrative. Follow these steps in order. Do not skip steps.
Confirm MCP is alive before touching anything else:
If any step fails, stop and fix MCP connectivity first. See Known Errors.
Run the full hierarchy extraction to understand what you're working with:
Look for:
material_slots)Run the material extraction to catch export-lossy setups before committing to an export:
Review all warnings before proceeding. Decide: bake procedural textures now, or patch materials at runtime after export.
The MCP server cannot handle GLTF exports (timeout). Always use headless CLI:
Critical flags:
export_apply=False — do not bake modifiers (Array modifier turns 1 MB into 56 MB)export_draco_mesh_compression_enable=False — apply Draco later via gltf-transformRun after a successful export. Always use individual steps, never optimize:
Expected size reduction: ~22 MB raw → ~3.7 MB (WebP) → ~1 MB (Draco). See references/texture-optimization.md for detailed metrics.
Run the full Post-Export Validation checklist below before shipping.
After every export, verify the following before handing off the GLB for integration:
npx @gltf-transform/cli inspect final.glb and check: mesh count, texture count, texture sizes, animation count, accessor sizes. No unexpected duplication.THREE.GLTFLoader: Unknown extension, missing texture files, unsupported Draco version.Scenario: You have a humanoid character with armature, 3 NLA actions (idle, walk, run), PBR texture set, and a weapon attached via parenting. You need a web-ready GLB for a Three.js scene.
Step 1: Health check and scene inspection
Step 2: Inspect the rig
Step 3: Check materials for export losses
Run the material extraction above. For a character, watch for:
Step 4: Export
Step 5: Verify animations exported
Expected output: 3 animations (Idle, Walk, Run). If 0, check that NLA strips are muted or the tracks are set to solo.
Step 6: Optimize
Step 7: Runtime animation setup (Three.js)
Scenario: After export, a metal panel material looks uniformly flat and shiny in Three.js. In Blender it had interesting roughness variation from a Noise Texture → Color Ramp → roughness input.
Step 1: Confirm the problem in Blender
Expected output reveals:
Step 2: Understand what GLTF received
The export exports the Principled BSDF's roughness input. When linked to a Color Ramp, GLTF exporter takes the default_value of the input socket (fallback), which is typically 0.5 — perfectly flat.
Step 3A: Fix by baking in Blender (best quality)
Then connect the new image texture node to the Roughness input and re-export.
Step 3B: Fix at runtime in Three.js (quick patch)
If you cannot bake, override the material roughness after load:
Step 4: Verify fix
Re-export and run validation checklist. In Babylon.js Sandbox, compare the metal panel material against a Blender viewport screenshot to confirm roughness variation is preserved.
The Blender MCP server cannot handle GLTF exports — they exceed the timeout. Always use headless CLI:
Set export_apply=False. Array modifiers (circular patterns, linear repeats) balloon file size when baked. Replicate them at runtime instead.
Example: 16 roller instances via Array modifier = ~1 MB GLB. Baked = ~56 MB GLB.
If you plan to optimize with gltf-transform, export without Draco compression. Re-encoding existing Draco corrupts meshes. Apply Draco as the final step.
These Blender node setups are lost on export:
| Node Setup | What's Lost | Workaround |
|---|---|---|
| Noise Texture → roughness | Entire procedural chain | Bake to texture, or shader patch at runtime |
| Color Ramp on roughness texture | Value remapping range | Manual roughness values, or runtime remap |
| Procedural bump (Noise → Bump) | Bump detail | Bake normal map in Blender |
| Mix Shader with complex factor | Blend logic | Simplify to single BSDF before export |
What DOES export: flat roughness/metallic values, image textures (without Color Ramp remapping), baked normal maps, PBR texture sets (baseColor, metallicRoughness, normal).
Blender names are transformed in GLTF:
| Blender | GLTF |
|---|---|
RINGS ball L | RINGS_ball_L |
Sphere.003 | Sphere003 |
RINGS L.001 | RINGS_L001 |
RINGS S (trailing space) | RINGS_S_ |
Always check names in the exported GLB, not Blender, when referencing meshes in code.
optimizeThe optimize command includes simplify which destroys mesh geometry. Use individual steps instead:
Blender project paths often contain spaces. Always double-quote:
Full hierarchy with materials, transforms, and modifiers:
| Setting | Value | Why |
|---|---|---|
export_format | 'GLB' | Single binary file |
export_apply | False | Don't bake modifiers (Array, etc.) |
export_animations | True | Include animation data |
export_nla_strips | True | Bake NLA strips into actions |
export_cameras | True | Include camera rigs |
export_lights | False | Handle lights in runtime (Three.js/R3F) |
export_draco_mesh_compression_enable | False | Apply Draco later via gltf-transform |
Target: smallest GLB with acceptable visual quality.
Key insights:
npx @gltf-transform/cli inspect model.glbSee references/texture-optimization.md for concrete commands and quality metrics.
Available through Blender MCP when configured:
| Integration | Capabilities |
|---|---|
| PolyHaven | Search, download, import free HDRIs, textures, and 3D models with auto material setup |
| Sketchfab | Search and download models (requires access token) |
| Hyper3D Rodin | Generate 3D models from text descriptions or reference images |
| Hunyuan3D | Create 3D assets from text prompts, images, or both |
See references/asset-integrations.md for usage examples and workflow patterns.
See references/errors.md for complete error tables.
print() + json.dumps() for small results (scene info, single object)tempfile.gettempdir() for large extraction results (full hierarchy, animation data, material reports)import bpy, json
def extract_hierarchy(obj, depth=0):
data = {
"name": obj.name,
"type": obj.type,
"location": list(obj.location),
"rotation": list(obj.rotation_euler),
"scale": list(obj.scale),
"visible": not obj.hide_viewport,
"children": [],
}
if obj.type == 'MESH' and obj.data:
data["vertices"] = len(obj.data.vertices)
data["faces"] = len(obj.data.polygons)
data["materials"] = [slot.material.name for slot in obj.material_slots if slot.material]
if obj.type == 'LIGHT':
data["light_type"] = obj.data.type
data["energy"] = obj.data.energy
data["color"] = list(obj.data.color)
for mod in obj.modifiers:
if mod.type == 'ARRAY':
data.setdefault("modifiers", []).append({
"type": "ARRAY",
"count": mod.count,
"offset_object": mod.offset_object.name if mod.offset_object else None,
})
for child in obj.children:
data["children"].append(extract_hierarchy(child, depth + 1))
return data
scene_data = {
"name": bpy.context.scene.name,
"fps": bpy.context.scene.render.fps,
"frame_start": bpy.context.scene.frame_start,
"frame_end": bpy.context.scene.frame_end,
"objects": [],
}
for obj in bpy.context.scene.objects:
if obj.parent is None:
scene_data["objects"].append(extract_hierarchy(obj))
print(json.dumps(scene_data, indent=2))import bpy, json
def extract_materials():
materials = []
for mat in bpy.data.materials:
if not mat.use_nodes:
continue
info = {"name": mat.name, "nodes": [], "warnings": []}
has_principled = False
for node in mat.node_tree.nodes:
node_data = {"type": node.type, "name": node.name}
if node.type == 'BSDF_PRINCIPLED':
has_principled = True
for inp in node.inputs:
if inp.is_linked:
node_data[inp.name] = "linked"
elif hasattr(inp, 'default_value'):
val = inp.default_value
try:
node_data[inp.name] = list(val)
except TypeError:
node_data[inp.name] = float(val)
if node.type == 'TEX_IMAGE' and node.image:
node_data["image"] = node.image.filepath
node_data["size"] = [node.image.size[0], node.image.size[1]]
if node.image.size[0] > 2048:
info["warnings"].append(f"Large texture: {node.image.filepath} ({node.image.size[0]}x{node.image.size[1]})")
if node.type in ('TEX_NOISE', 'TEX_VORONOI', 'TEX_WAVE', 'TEX_MUSGRAVE'):
info["warnings"].append(f"Procedural texture node '{node.name}' ({node.type}) will be LOST on GLTF export")
if node.type == 'VALTORGB': # Color Ramp
info["warnings"].append(f"Color Ramp '{node.name}' remapping will be LOST on GLTF export")
if not has_principled:
info["warnings"].append("No Principled BSDF found — export result unpredictable")
info["nodes"].append(node_data)
materials.append(info)
return materials
result = extract_materials()
for mat in result:
if mat["warnings"]:
print(f"WARN [{mat['name']}]: {'; '.join(mat['warnings'])}")
print(json.dumps(result, indent=2))# Use 'blender' if it's on PATH, otherwise use the platform-specific path:
# macOS: /Applications/Blender.app/Contents/MacOS/Blender
# Windows: "C:\Program Files\Blender Foundation\Blender 4.x\blender.exe"
# Linux: /usr/bin/blender
blender \
--background "/path/to/scene.blend" \
--python-expr "
import bpy, os
export_path = '/path/to/output.glb'
os.makedirs(os.path.dirname(os.path.abspath(export_path)), exist_ok=True)
bpy.ops.export_scene.gltf(
filepath=export_path,
export_format='GLB',
export_apply=False,
export_animations=True,
export_nla_strips=True,
export_cameras=True,
export_lights=False,
export_draco_mesh_compression_enable=False,
)
size_mb = os.path.getsize(export_path) / 1024 / 1024
print(f'Export complete: {export_path} ({size_mb:.1f} MB)')
"# 1. Inspect raw export first
npx @gltf-transform/cli inspect output.glb
# 2. Resize textures (max 1K for web/mobile)
npx @gltf-transform/cli resize output.glb resized.glb --width 1024 --height 1024
# 3. WebP compression (quality 90 preserves detail)
npx @gltf-transform/cli webp resized.glb webp.glb --quality 90
# 4. Draco mesh compression (LAST — irreversible)
npx @gltf-transform/cli draco webp.glb final.glb
# 5. Inspect final result
npx @gltf-transform/cli inspect final.glb# MCP tool calls
get_scene_info
execute_python: print("ok")import bpy, json
# Check armature and NLA strips
for obj in bpy.data.objects:
if obj.type == 'ARMATURE':
print(f"Armature: {obj.name}")
if obj.animation_data:
print(f" Active action: {obj.animation_data.action.name if obj.animation_data.action else 'None'}")
for track in obj.animation_data.nla_tracks:
print(f" NLA track: {track.name}")
for strip in track.strips:
print(f" Strip: {strip.name}, frames {strip.frame_start}-{strip.frame_end}")blender \
--background "/path/to/character.blend" \
--python-expr "
import bpy, os, tempfile
export_dir = tempfile.gettempdir()
bpy.ops.export_scene.gltf(
filepath=os.path.join(export_dir, 'character.glb'),
export_format='GLB',
export_apply=False,
export_animations=True,
export_nla_strips=True,
export_cameras=False,
export_lights=False,
export_draco_mesh_compression_enable=False,
export_skins=True,
export_morph=True,
)
print('done:', os.path.getsize(os.path.join(export_dir, 'character.glb')) / 1024 / 1024, 'MB')
"npx @gltf-transform/cli inspect character.glb | grep -i animnpx @gltf-transform/cli resize character.glb char_resized.glb --width 1024 --height 1024
npx @gltf-transform/cli webp char_resized.glb char_webp.glb --quality 90
npx @gltf-transform/cli draco char_webp.glb character_final.glbimport { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';
import { DRACOLoader } from 'three/addons/loaders/DRACOLoader.js';
import * as THREE from 'three';
const dracoLoader = new DRACOLoader();
dracoLoader.setDecoderPath('/draco/');
const loader = new GLTFLoader();
loader.setDRACOLoader(dracoLoader);
loader.load('/character_final.glb', (gltf) => {
const mixer = new THREE.AnimationMixer(gltf.scene);
const clips = gltf.animations; // [Idle, Walk, Run]
const idleAction = mixer.clipAction(clips.find(c => c.name === 'Idle'));
idleAction.play();
// Animate mixer in render loop: mixer.update(delta)
});import bpy, json
mat = bpy.data.materials.get("MetalPanel")
if mat and mat.use_nodes:
for node in mat.node_tree.nodes:
print(f"Node: {node.type} - {node.name}")
for inp in node.inputs:
if inp.is_linked:
print(f" Input '{inp.name}': linked to something")Node: BSDF_PRINCIPLED - Principled BSDF
Input 'Roughness': linked to something
Node: VALTORGB - Color Ramp <-- this will NOT export
Node: TEX_NOISE - Noise Texture <-- this will NOT exportimport bpy
# Select the object
obj = bpy.data.objects["MetalPanelMesh"]
bpy.context.view_layer.objects.active = obj
bpy.ops.object.select_all(action='DESELECT')
obj.select_set(True)
# Create a new image to bake into
bake_img = bpy.data.images.new("MetalPanel_roughness_baked", width=1024, height=1024)
bake_img.colorspace_settings.name = 'Non-Color'
# Add image texture node to material
mat = obj.active_material
nodes = mat.node_tree.nodes
img_node = nodes.new('ShaderNodeTexImage')
img_node.image = bake_img
nodes.active = img_node
# Bake roughness (use ROUGHNESS pass or EMIT trick)
bpy.context.scene.cycles.bake_type = 'ROUGHNESS'
bpy.ops.object.bake(type='ROUGHNESS', save_mode='INTERNAL')
# Save baked image
import tempfile, os
bake_path = os.path.join(tempfile.gettempdir(), 'MetalPanel_roughness_baked.png')
bake_img.filepath_raw = bake_path
bake_img.file_format = 'PNG'
bake_img.save()
print(f"Baked roughness to {bake_path}")loader.load('/metal_panel.glb', (gltf) => {
gltf.scene.traverse((child) => {
if (child.isMesh && child.material) {
const mats = Array.isArray(child.material) ? child.material : [child.material];
mats.forEach(mat => {
if (mat.name === 'MetalPanel') {
// Instead of flat 0.5, set a textured roughness or varied value
mat.roughness = 0.3; // adjust to match intended look
mat.metalness = 0.9;
mat.needsUpdate = true;
}
});
}
});
});blender --background "scene.blend" --python-expr "
import bpy, os
export_path = 'output.glb'
os.makedirs(os.path.dirname(export_path), exist_ok=True)
bpy.ops.export_scene.gltf(
filepath=export_path,
export_format='GLB',
export_apply=False,
export_animations=True,
export_nla_strips=True,
export_cameras=True,
export_lights=False,
export_draco_mesh_compression_enable=False,
)
print(f'Size: {os.path.getsize(export_path)/1024/1024:.1f} MB')
"# Resize textures (max 1024x1024)
npx @gltf-transform/cli resize input.glb resized.glb --width 1024 --height 1024
# WebP texture compression
npx @gltf-transform/cli webp resized.glb webp.glb --quality 90
# Draco mesh compression (LAST step)
npx @gltf-transform/cli draco webp.glb output.glbblender --background "$HOME/Downloads/blend 3/scene.blend" ...import bpy, json
def extract_hierarchy(obj, depth=0):
data = {
"name": obj.name,
"type": obj.type,
"location": list(obj.location),
"rotation": list(obj.rotation_euler),
"scale": list(obj.scale),
"visible": not obj.hide_viewport,
"children": [],
}
if obj.type == 'MESH' and obj.data:
data["vertices"] = len(obj.data.vertices)
data["faces"] = len(obj.data.polygons)
data["materials"] = [slot.material.name for slot in obj.material_slots if slot.material]
if obj.type == 'LIGHT':
data["light_type"] = obj.data.type
data["energy"] = obj.data.energy
data["color"] = list(obj.data.color)
if obj.data.type == 'AREA':
data["size"] = obj.data.size
data["size_y"] = obj.data.size_y
# Array modifiers (important for runtime replication)
for mod in obj.modifiers:
if mod.type == 'ARRAY':
data.setdefault("modifiers", []).append({
"type": "ARRAY",
"count": mod.count,
"offset_object": mod.offset_object.name if mod.offset_object else None,
})
for child in obj.children:
data["children"].append(extract_hierarchy(child, depth + 1))
return data
scene_data = {
"name": bpy.context.scene.name,
"fps": bpy.context.scene.render.fps,
"frame_start": bpy.context.scene.frame_start,
"frame_end": bpy.context.scene.frame_end,
"objects": [],
}
for obj in bpy.context.scene.objects:
if obj.parent is None:
scene_data["objects"].append(extract_hierarchy(obj))
print(json.dumps(scene_data, indent=2))import bpy, json
def extract_materials():
materials = []
for mat in bpy.data.materials:
if not mat.use_nodes:
continue
info = {"name": mat.name, "nodes": []}
for node in mat.node_tree.nodes:
node_data = {"type": node.type, "name": node.name}
if node.type == 'BSDF_PRINCIPLED':
for inp in node.inputs:
if inp.is_linked:
node_data[inp.name] = "linked"
elif hasattr(inp, 'default_value'):
val = inp.default_value
try:
node_data[inp.name] = list(val)
except TypeError:
node_data[inp.name] = float(val)
if node.type == 'TEX_IMAGE' and node.image:
node_data["image"] = node.image.filepath
node_data["size"] = [node.image.size[0], node.image.size[1]]
info["nodes"].append(node_data)
materials.append(info)
return materials
print(json.dumps(extract_materials(), indent=2))import bpy, json
def extract_animation(obj):
if not obj.animation_data or not obj.animation_data.action:
return None
tracks = []
for fc in obj.animation_data.action.fcurves:
keyframes = []
for kp in fc.keyframe_points:
keyframes.append({
"frame": int(kp.co[0]),
"value": float(kp.co[1]),
"interpolation": kp.interpolation,
})
tracks.append({
"data_path": fc.data_path,
"index": fc.array_index,
"keyframes": keyframes,
})
return {"object": obj.name, "tracks": tracks}
animations = []
for obj in bpy.data.objects:
anim = extract_animation(obj)
if anim:
animations.append(anim)
print(json.dumps(animations, indent=2))Blender export (no Draco) → resize (1K max) → WebP (q90) → Draco
~22 MB ~3.7 MB ~3.7 MB ~1 MB