Blender MCP

Your agent can edit or model a part in Blender, export a verified STL, and hand it to the slicer and printer tools in this server. No Blender knowledge needed: ask for the result ("make this case fit my phone") and the agent does the modelling through a Blender MCP server.

This server does not bundle Blender. It connects to a standard Blender MCP server, mcp-for-blender (formerly blender-mcp), as an MCP client over stdio. Printer tools work without Blender configured.

Set it up

1. Install Blender and uv.

2. Install the matching Blender addon: uvx mcp-for-blender install-addon, or download addon.py from the mcp-for-blender repository and install it under Edit → Preferences → Add-ons. Enable it.

3. Open Blender. The addon starts its connection automatically (see the MCP for Blender sidebar tab). Keep Blender open while your agent works: the addon does not run in background (blender -b) mode.

4. Give this server two settings (your agent can do this during setup):

   • BLENDER_MCP_COMMAND: the full path to uvx
   • BLENDER_MCP_ARGS: ["mcp-for-blender"]

   Optional: BLENDER_HOST / BLENDER_PORT if the addon listens somewhere other than localhost:9876, and BLENDER_MCP_TIMEOUT_MS (default 120000). Blender and this server must share a filesystem, because STL paths are passed between them.

Check it: ask your agent to call blender_mcp_status with connect: true. It lists the Blender tools it discovered. A connected MCP server does not by itself prove the addon is running; get_scene_info through blender_mcp_call does.

How the pieces fit

Step	Tool	What it does
Inspect the input	get_stl_info	Size, bounding box, and triangle count of the downloaded model
Discover Blender	blender_mcp_status	Tool names and summaries; tool_names returns full schemas for the tools you'll call
Model or edit	blender_mcp_call	Forwards any Blender MCP tool, usually execute_blender_code, with the user's own words in user_prompt
Export for printing	blender_mcp_export_stl	Writes named scene objects to a new STL and reports the measured size
Quick mesh fixes	blender_mcp_edit_model	Imports an STL, applies decimate, remesh, or boolean_union, and exports a new STL
Slice and print	slice_stl, print_3mf, …	The usual printer path, with all print safety checks

blender_mcp_export_stl exists because Blender MCP's own export_scene writes GLB or FBX, not STL. The export reads the evaluated geometry (modifiers applied) in world space and writes it directly, so it never changes your selection, active object, or mode. It checks Blender's receipt, validates the file, refuses to overwrite anything, and returns output_verified: true with the triangle count and bounding_box.dimensions measured from the written bytes.

Units. STL files carry no units; slicers read them as millimetres. An STL imported into Blender keeps its numbers (163.4 mm becomes 163.4 Blender units), so export it with the default scale: 1. If the agent modelled from scratch in real metres, the export warns that the part is under 1 unit across; export again with scale: 1000. Always compare the reported dimensions with what you expect before slicing.

Worked example: refit a phone case for a new phone

This example ran end to end through this server on 2026-09-29: Blender 5.0.1 with mcp-for-blender 2.1.1, driven by an MCP client over stdio. The request:

"Here's an iPhone 16 Pro Max case. Make it fit my iPhone 17 Pro Max."

1. Get the model and the facts. The agent downloaded a free case (iPhone 16 Pro Max Case by Andrej on Printables, CC BY-NC-SA) and Apple's official dimensional drawings for both phones. get_stl_info reported the case at 167.2 × 81.8 × 12.25 mm.
2. Measure the case in Blender. Through execute_blender_code, it imported the STL and ray-cast the inside: a 164.2 × 77.8 mm cavity (so the designer left 1.2 mm of length and 0.2 mm of width play), 1.5–2 mm walls, a camera opening in one corner, and cut-outs for the action button and Camera Control.
3. Compare the phones. Apple's drawings put the 17 Pro Max at 163.43 × 77.98 × 8.75 mm (16 Pro Max: 163.03 × 77.58 × 8.25). Every button sits exactly 0.20 mm further from the top, which is the same position relative to the phone's centre. The camera changed completely: a full-width plateau raised 2.55 mm, about 70 mm wide and reaching 48 mm down from the top edge, and the bottom speaker ports extend 4.9 mm further on one side.
4. Refit, don't scale. Scaling would thicken walls and move buttons. Instead the agent stretched the case at its centre planes: +0.2 mm per side in length and width, and +0.5 mm of depth above the phone's mid-line, which also moves the button openings up the 0.25 mm the new phone needs. It cut a plateau opening with 1.0 mm lengthwise and 0.5 mm crosswise clearance, added three speaker holes, and filled a 1.6 mm border around the new opening so no half-cut grill holes were left as thin slivers.
5. Check the fit. It built a phone stand-in from Apple's numbers and intersected it with the case: the camera plateau cleared by 0 mm³ of overlap, and the body overlapped only 7.8 mm³ along the bottom 0.28 mm of the cavity edge, where the stand-in's square edges meet the case's small fillet (the real phone's edges are rounded). The same check against the original case overlapped 283 mm³, which confirms the test catches a real misfit.
6. Export and verify. blender_mcp_export_stl wrote a new 167.6 × 82.2 × 12.75 mm STL (194,652 triangles, no non-manifold edges).
7. Slice. slice_stl sliced it with the installed Bambu Studio for a P1S with a 0.4 mm nozzle and Bambu TPU 95A HF (flexible, as phone cases usually are): 230 °C nozzle, 35 °C textured plate, about 1 h 38 min and 21 g of filament. The next step is the print tools, which check the file and the printer and ask before starting.

Evidence levels: geometry, fit calculations, file validation, and slicing were checked in software. The printed case, snap fit, and TPU behaviour were not tested in this run, and the plateau's lower edge is not dimensioned on Apple's drawing, so it was scaled from the drawing (±0.3 mm) and given extra clearance.

Check a Blender install end to end

scripts/blender-live-check.mjs launches a separate Blender with factory settings (never your open scene), loads the addon on a spare port, drives this server over stdio, and checks that an exported 40 × 20 × 10 box measures exactly that:

npm run build
BLENDER_EXECUTABLE=/Applications/Blender.app/Contents/MacOS/Blender \
BLENDER_ADDON_PATH=/path/to/mcp-for-blender/addon.py \
node scripts/blender-live-check.mjs

Safety and limits

• blender_mcp_call can change your open scene. Calls are never retried automatically; after a timeout, look at Blender before trying again, because the request may still be running.
• Blender executables come only from server configuration. Per-call executable overrides stay disabled unless MCP_ALLOW_EXECUTABLE_ARG=1.
• Printer access codes and other server secrets are not passed to the Blender process; only BLENDER_* settings are.
• A valid STL is not a guarantee of a good print. Check the reported dimensions, slice it, and look at the preview before printing.
• BLENDER_MCP_BRIDGE_COMMAND keeps older custom bridge executables working for blender_mcp_edit_model; their results report output_verified: false.