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.

• Two-angle design. A human at a keyboard (Claude Desktop, ChatGPT Desktop — no crypto wallet) gets real answers with zero payment from the everyday tools: list_printers, check_printability, analyze_model, get_print_quote. These call FabTally's free, rate-limited public endpoints. An autonomous agent with a wallet gets the heavier/exact tools — optimize_orientation, slice_model, and the full (full=true) DFM report — metered over x402 (USDC on Base). With no payment supplied, those return the x402 challenge (price, network, asset, payTo) so the calling agent knows the cost and can pay and retry.
• This server holds no private key and persists no models. It only relays calls to https://fabtally.com/...; uploaded models are streamed to the slicer, never stored.

Tools

The free tools are rate-limited public endpoints — fine for a human exploring a design, not for high-volume or production integrations. For unlimited, machine-speed access, an autonomous agent with a wallet can pay per call via x402: the premium tools above, or check_printability with full=true for the exact (slice-derived) DFM report.

The 12 printers

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 for local files) — a public https URL to an STL / 3MF / OBJ / PLY / STEP file. The server fetches it. (Try https://fabtally.com/sample-cube-20mm.stl.) Got a file on your machine — Claude Desktop, ChatGPT Desktop? Drop it at https://fabtally.com/upload (no account, drag-and-drop) to get a short-lived URL back (auto-deletes in ~2 hours, nothing kept), then pass that URL as model_url. That page also has a "Get quote now" button for an instant human-readable quote with zero MCP involved.
• model_base64 + filename — the raw file bytes, base64-encoded, plus a filename (e.g. "cube.stl") so the file type is known. Only reliable for small files (roughly <50KB). MCP clients truncate large inline tool-call arguments, so a real STL sent this way can silently arrive as a corrupted fragment and produce garbage results (wrong dimensions, bogus quotes) with no error. For anything bigger, use model_url via the upload bridge above.

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 (premium, x402-metered; returns x402 challenge unless x_payment is supplied)
{ "name": "check_printability",
  "arguments": { "model_url": "https://example.com/bracket.stl",
                 "full": true, "printer": "bambu-p1s", "material": "petg" } }

// 4) Price quote, base64 model, 10 parts (free, real result, no payment)
{ "name": "get_print_quote",
  "arguments": { "model_base64": "<...>", "filename": "part.stl",
                 "material": "pla", "quantity": 10 } }

// 5) Least-support orientation (premium, x402-metered, $0.02)
{ "name": "optimize_orientation",
  "arguments": { "model_url": "https://example.com/handle.stl", "printer": "prusa-mk4" } }

// 6) Slice with a preview PNG (premium, x402-metered tier, $0.01)
{ "name": "slice_model",
  "arguments": { "model_url": "https://example.com/gear.stl",
                 "printer": "voron-24-350", "material": "abs",
                 "quality": "standard", "include_preview": 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