Blender MCP

Control a running Blender instance from Hermes via socket on TCP port 9876.

Setup (one-time)

1. Install the Blender addon

curl -sL https://raw.githubusercontent.com/ahujasid/blender-mcp/main/addon.py -o ~/Desktop/blender_mcp_addon.py

In Blender: Edit > Preferences > Add-ons > Install > select blender_mcp_addon.py Enable "Interface: Blender MCP"

2. Start the socket server in Blender

Press N in Blender viewport to open sidebar. Find "BlenderMCP" tab and click "Start Server".

3. Verify connection

nc -z -w2 localhost 9876 && echo "OPEN" || echo "CLOSED"

Protocol

Plain UTF-8 JSON over TCP -- no length prefix.

Send: {"type": "<command>", "params": {<kwargs>}} Receive: {"status": "success", "result": <value>} {"status": "error", "message": "<reason>"}

Available Commands

Python Helper

Use this inside execute_code tool calls:

import socket, json

def blender_exec(code: str, host="localhost", port=9876, timeout=15):
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((host, port))
    s.settimeout(timeout)
    payload = json.dumps({"type": "execute_code", "params": {"code": code}})
    s.sendall(payload.encode("utf-8"))
    buf = b""
    while True:
        try:
            chunk = s.recv(4096)
            if not chunk:
                break
            buf += chunk
            try:
                json.loads(buf.decode("utf-8"))
                break
            except json.JSONDecodeError:
                continue
        except socket.timeout:
            break
    s.close()
    return json.loads(buf.decode("utf-8"))

Common bpy Patterns

Clear scene

bpy.ops.object.select_all(action='SELECT')
bpy.ops.object.delete()

Add mesh objects

bpy.ops.mesh.primitive_uv_sphere_add(radius=1, location=(0, 0, 0))
bpy.ops.mesh.primitive_cube_add(size=2, location=(3, 0, 0))
bpy.ops.mesh.primitive_cylinder_add(radius=0.5, depth=2, location=(-3, 0, 0))

Create and assign material

mat = bpy.data.materials.new(name="MyMat")
mat.use_nodes = True
bsdf = mat.node_tree.nodes.get("Principled BSDF")
bsdf.inputs["Base Color"].default_value = (R, G, B, 1.0)
bsdf.inputs["Roughness"].default_value = 0.3
bsdf.inputs["Metallic"].default_value = 0.0
obj.data.materials.append(mat)

Keyframe animation

obj.location = (0, 0, 0)
obj.keyframe_insert(data_path="location", frame=1)
obj.location = (0, 0, 3)
obj.keyframe_insert(data_path="location", frame=60)

Render to file

bpy.context.scene.render.filepath = "/tmp/render.png"
bpy.context.scene.render.engine = 'CYCLES'
bpy.ops.render.render(write_still=True)

Pitfalls

• Must check socket is open before running (nc -z localhost 9876)
• Addon server must be started inside Blender each session (N-panel > BlenderMCP > Connect)
• Break complex scenes into multiple smaller execute_code calls to avoid timeouts
• Render output path must be absolute (/tmp/...) not relative
• shade_smooth() requires object to be selected and in object mode