FabTally MCP Server

The first MCP server for real FDM 3D-printing slicing, quoting, and DFM / printability analysis. Every other 3D-printing MCP just drives a printer (OctoPrint, Bambu). None of them slice, quote, or run design-for-manufacturability checks — FabTally does.

It fronts the FabTally agent API (https://fabtally.com), which runs a production slicing engine against 12 calibrated FDM printer profiles and 12 filament materials, and exposes it as MCP tools so any MCP-capable agent (Claude Desktop, Cursor, custom agents) can discover and call it.

• Free for people; per-call for agents. A human at a keyboard (Claude Desktop, ChatGPT Desktop — no crypto wallet) gets real answers with zero payment from every useful tool: slice metrics (print time, filament, layers, cost), full DFM, orientation optimisation, and the printer/material/settings advisors — subject to generous fair-use daily limits so the free compute can't be farmed. Only the downloadable G-code file (and the preview PNG) — the commercial deliverable — is paid, via x402 (USDC on Base) or prepaid credits, for agents, production and high volume. Hit the daily limit and you get a friendly pointer to prepaid credits (https://fabtally.com/buy) or the x402 agent lane.

• This server holds no private key and persists no models. It relays calls to https://fabtally.com/...; uploaded models are streamed to the slicer, never stored.

Tools

All tools are FREE for personal & interactive use (fair-use daily limits). Only slice_model with include_gcode/include_preview is paid.

Related MCP server: PrusaMCP

The 13 printers

Default: elegoo-centauri-carbon.

Materials: pla, pla-cf, petg, petg-cf, abs, abs-cf, asa, asa-cf, nylon, pc, pet, tpu (PLA/PETG/ABS/ASA + carbon-fiber variants, Nylon, PC, PET, TPU). list_printers always returns the authoritative live list.

Supplying a model file

MCP tools can't take raw file uploads, so every model-consuming tool accepts the model two ways — pick one:

• model_url (PREFERRED) — just paste a link. The server fetches and, if needed, unpacks it:

  • a direct https URL to an STL / 3MF / OBJ / PLY / STEP file;

  • a Thingiverse, Printables or MakerWorld model page is tried, but these sites usually block downloads from servers (HTTP 403). You'll get a clear message to download the file yourself and upload it;

  • a GitHub blob URL (auto-rewritten to raw);

  • a Google Drive or Dropbox share link (auto-rewritten to the direct-download form);

  • a .zip archive — the first printable model inside (STL/3MF/OBJ/PLY/STEP) is extracted and used, and the response reports which file it picked.

  Local file? Drop it once at https://fabtally.com/upload (no account, drag-and-drop) to get a short-lived URL (auto-deletes in ~2h, nothing kept), then paste that URL as model_url. Max 64 MB.

• model_base64 + filename — raw file bytes, base64, plus a filename. Small-file fallback only (roughly <50KB). MCP clients truncate large inline arguments, so a real STL sent this way can silently arrive corrupted. For anything bigger, use model_url via the upload bridge.

Example tool calls

// 1) Discover printers/materials/pricing (free)
{ "name": "list_printers", "arguments": {} }

// 2) Free printability check on a hosted model
{ "name": "check_printability",
  "arguments": { "model_url": "https://fabtally.com/sample-cube-20mm.stl" } }

// 3) Full DFM report (free for interactive use) — paste a GitHub link
{ "name": "check_printability",
  "arguments": { "model_url": "https://github.com/user/repo/blob/main/bracket.stl",
                 "full": true, "printer": "bambu-p1s", "material": "petg" } }

// 4) Slice metrics (free) — no wallet, real print time / filament / cost
{ "name": "slice_model",
  "arguments": { "model_url": "https://raw.githubusercontent.com/CreativeTools/3DBenchy/master/Single-part/3DBenchy.stl",
                 "printer": "prusa-mk4", "material": "pla" } }

// 5) Compare your printers (free)
{ "name": "compare_printers",
  "arguments": { "model_url": "https://.../part.zip",
                 "printers": "bambu-a1,prusa-mk4,ender3-v3", "material": "petg" } }

// 6) The G-code FILE (PAID) — returns an x402 402 challenge unless x_payment/api_key is supplied
{ "name": "slice_model",
  "arguments": { "model_url": "https://example.com/gear.stl",
                 "printer": "voron-24-350", "material": "abs", "include_gcode": true } }

Install

cd fabtally-mcp-server
npm install

Run (stdio — primary)

node index.js
# or, after `npm install -g .`:  fabtally-mcp

The server speaks MCP over stdio. Point your MCP client at it.

Claude Desktop / MCP client config

{
  "mcpServers": {
    "fabtally": {
      "command": "node",
      "args": ["/absolute/path/to/fabtally-mcp-server/index.js"]
    }
  }
}

Run (Streamable HTTP — optional)

MCP_HTTP_PORT=8103 node http.js
# POST MCP JSON-RPC messages to http://127.0.0.1:8103/mcp   (stateless)

Configuration

How paid calls work (x402)

1. Call a paid tool (or check_printability with full: true) without x_payment. You get { "payment_required": true, "http_status": 402, "challenge": { ... } } containing the x402 accepts entry (scheme exact, network eip155:8453 = Base, asset USDC, atomic amount, payTo).

2. Build an x402 payment authorization (EIP-3009 transferWithAuthorization to payTo) for that entry using your x402 client / wallet.

3. Call the tool again with the resulting token in the x_payment argument. The server forwards it as the X-PAYMENT header and returns the actual result.

Free discovery is always at GET https://fabtally.com/agent/overview; the OpenAPI contract at https://fabtally.com/openapi.json; x402 discovery at https://fabtally.com/.well-known/x402.

Test

node smoke-test.mjs   # lists tools, calls list_printers + check_printability, checks paid 402s

License

MIT · Sunstone Soft · https://fabtally.com