Blender MCP

Blender MCP

Tool Selection

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.

Health Check (Always First)

1. get_scene_info — verify connection (default port 9876)
2. execute_python with print("ok") — verify Python works
3. screenshot — verify viewport capture works

If MCP is unresponsive, check that the Blender MCP addon is enabled and the socket server is running.

Complete Export Workflow

This is the end-to-end linear narrative. Follow these steps in order. Do not skip steps.

Step 1: Health Check

Confirm MCP is alive before touching anything else:

# In MCP tool call:
get_scene_info
execute_python: print("ok")
screenshot

If any step fails, stop and fix MCP connectivity first. See Known Errors.

Step 2: Inspect Scene

Run the full hierarchy extraction to understand what you're working with:

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))

Look for:

• Array modifiers (will balloon file size if baked — must replicate at runtime)
• Objects with many vertices (risk of slow export or large GLB)
• Hidden objects you may or may not want to export
• Missing materials (empty material_slots)

Step 3: Verify Materials

Run the material extraction to catch export-lossy setups before committing to an export:

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))

Review all warnings before proceeding. Decide: bake procedural textures now, or patch materials at runtime after export.

Step 4: Export via Headless CLI

The MCP server cannot handle GLTF exports (timeout). Always use headless CLI:

# 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)')
"

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-transform
• Quote all paths that may contain spaces

Step 5: Optimize with gltf-transform

Run after a successful export. Always use individual steps, never optimize:

# 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

Expected size reduction: ~22 MB raw → ~3.7 MB (WebP) → ~1 MB (Draco). See references/texture-optimization.md for detailed metrics.

Step 6: Validate

Run the full Post-Export Validation checklist below before shipping.

Post-Export Validation Checklist

After every export, verify the following before handing off the GLB for integration:

• File size is reasonable — raw GLB under 30 MB, optimized GLB under 5 MB for typical web scenes. Flag anything above these thresholds.
• Inspect with gltf-transform CLI — run npx @gltf-transform/cli inspect final.glb and check: mesh count, texture count, texture sizes, animation count, accessor sizes. No unexpected duplication.
• Visual test in Babylon.js Sandbox — drag-and-drop the GLB at sandbox.babylonjs.com. Verify: mesh renders correctly, textures appear, animations play, no black/pink materials.
• No Three.js console errors — load in a minimal Three.js GLTFLoader test page and check browser console. Common errors: THREE.GLTFLoader: Unknown extension, missing texture files, unsupported Draco version.
• Materials spot-check — pick 3–5 materials and visually confirm roughness, metalness, and base color look correct. Compare against Blender viewport render. Flag any that look flat or overly shiny.
• Animation spot-check — if the scene has animations, verify at least one plays correctly in Babylon.js Sandbox or Three.js. Check frame count matches expected.
• Name mapping verified — if runtime code references mesh names, confirm the names match after GLTF export transformation (spaces → underscores, dots removed). See Critical Rule 5.
• No missing textures — check Babylon.js Sandbox network tab. No 404s for texture files. All textures should be packed inside the GLB.

Examples

Example 1: Export Character Rig with Animations

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

# MCP tool calls
get_scene_info
execute_python: print("ok")

Step 2: Inspect the rig

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}")

Step 3: Check materials for export losses

Run the material extraction above. For a character, watch for:

• Procedural skin texture nodes (Noise → color variation) — these will be lost
• Color Ramp on roughness for fabric — will be lost, roughness will look flat
• Decision: bake procedural variations to image textures, or patch roughness values at runtime

Step 4: Export

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')
"

Step 5: Verify animations exported

npx @gltf-transform/cli inspect character.glb | grep -i anim

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

npx @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.glb

Step 7: Runtime animation setup (Three.js)

import { 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)
});

Example 2: Debug Material Export Loss (Roughness Looks Flat)

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

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")

Expected output reveals:

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 export

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)

import 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}")

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:

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;
                }
            });
        }
    });
});

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.

Critical Rules

1. MCP Server Times Out on Exports

The Blender MCP server cannot handle GLTF exports — they exceed the timeout. Always use headless CLI:

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')
"

2. Do NOT Apply Modifiers on Export

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.

3. Export WITHOUT Draco First

If you plan to optimize with gltf-transform, export without Draco compression. Re-encoding existing Draco corrupts meshes. Apply Draco as the final step.

4. Procedural Textures Don't Export to GLTF

These Blender node setups are lost on export:

What DOES export: flat roughness/metallic values, image textures (without Color Ramp remapping), baked normal maps, PBR texture sets (baseColor, metallicRoughness, normal).

5. GLTF Name Mapping

Blender names are transformed in GLTF:

• Spaces → underscores
• Dots → removed
• Trailing spaces → trailing underscore

Always check names in the exported GLB, not Blender, when referencing meshes in code.

6. Never Use gltf-transform optimize

The optimize command includes simplify which destroys mesh geometry. Use individual steps instead:

# 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.glb

7. Quote Paths with Spaces

Blender project paths often contain spaces. Always double-quote:

blender --background "$HOME/Downloads/blend 3/scene.blend" ...

Scene Extraction Pattern

Full hierarchy with materials, transforms, and modifiers:

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))

Material Extraction Pattern

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))

Animation Keyframe Extraction

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))

GLTF Export Settings Reference

Texture Optimization Pipeline

Target: smallest GLB with acceptable visual quality.

Blender export (no Draco) → resize (1K max) → WebP (q90) → Draco
   ~22 MB                    ~3.7 MB           ~3.7 MB      ~1 MB

Key insights:

• 4K textures (4096x4096) = ~89 MB GPU memory per texture. 1K = ~5.6 MB. 16x reduction.
• PNG metallicRoughness textures compress well to WebP at quality 85-90.
• Mobile GPUs (Adreno, Mali) benefit most from texture downscaling.
• Inspect with: npx @gltf-transform/cli inspect model.glb

See references/texture-optimization.md for concrete commands and quality metrics.

Asset Integrations

Available through Blender MCP when configured:

See references/asset-integrations.md for usage examples and workflow patterns.

Known Errors & Workarounds

See references/errors.md for complete error tables.

Data Output

• print() + json.dumps() for small results (scene info, single object)
• Use tempfile.gettempdir() for large extraction results (full hierarchy, animation data, material reports)
• Always include metadata: scene name, fps, frame range, Blender version