blender-mcp

Blender MCP Skill

Companion skill for the blender entry in the Hermes MCP catalog. The MCP server provides the connection to Blender; this skill teaches the bpy idioms and pitfalls for driving it well. It does not cover Blender UI workflows — everything here goes through the MCP tools against a live Blender session.

When to Use

Use when the user wants to create or modify anything in a running Blender instance: meshes, materials, animations, lighting, renders. Requires the blender MCP server installed and a Blender desktop session with the addon connected.

Prerequisites

1. Install the MCP server from the Nous catalog (one-time):

   hermes mcp install blender
   

   This configures the pinned blender-mcp stdio server with the curated tool set: get_scene_info, get_object_info, get_viewport_screenshot, execute_blender_code.

2. Install the addon inside Blender (one-time — the catalog entry's post-install notes cover this too):

   • Download https://raw.githubusercontent.com/ahujasid/blender-mcp/main/addon.py
   • Blender > Edit > Preferences > Add-ons > Install... > select addon.py, enable "Interface: Blender MCP".

3. Every session: start Blender FIRST, press N in the viewport, open the "BlenderMCP" tab, click "Connect to Claude" (starts the local bridge socket). Then start your Hermes session so the MCP tools are loaded.

   The addon refuses to start under blender -b (background mode). On a machine without a display, run Blender under a virtual one: xvfb-run blender. GPU rendering works fine under Xvfb.

Quick Reference

Deeper material lives in the reference files (load on demand):

Optional asset-service tools (PolyHaven, Sketchfab, Hyper3D, Hunyuan3D) are disabled by default. If the user has enabled a service in the addon panel, opt into its tools with hermes mcp configure blender.

Procedure

1. Call get_scene_info first — never assume the scene is empty.
2. Build with execute_blender_code, in small focused calls (one logical step per call: add objects, then materials, then animation). Large monolithic scripts hit the bridge timeout.
3. Verify visually with get_viewport_screenshot between major steps.
4. Render to an absolute path and tell the user where the file is.

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

• The blender MCP tools only exist if the server is installed and the session started after install. If they're missing, run hermes mcp install blender and start a new session.
• The addon bridge must be (re)connected inside Blender each Blender session (N-panel > BlenderMCP > Connect). "Connection refused" from the tools means Blender isn't running or the addon isn't connected — fix that, don't retry.
• Break complex scenes into multiple smaller execute_blender_code calls to avoid bridge timeouts.
• Render output paths must be absolute (/tmp/render.png), not relative — they resolve on the BLENDER host's filesystem, which matters if Hermes and Blender run on different machines.
• shade_smooth() requires the object to be selected and in object mode.
• execute_blender_code runs arbitrary Python inside Blender with no sandbox — same trust level as the terminal tool. Don't paste untrusted code into it.
• Do NOT hand-roll raw TCP JSON to port 9876 from execute_code — that was this skill's pre-MCP workaround. It bypasses the catalog's version pinning and tool curation. The MCP tools are the supported path.

Verification

• get_scene_info returns the expected object list after each build step.
• get_viewport_screenshot shows the scene you intended.
• After a render, confirm the output file exists and report its absolute path to the user.