printfins.com for an AI client: Claude Code, Claude Desktop, or any app that speaks the Model Context Protocol. Ask it to "fin every STL in this folder at 35° on Y" and it calls the tools below on the files on your computer.

It is the command line underneath: a tool call becomes the CLI's arguments and cli.js does the work, so the fins, the file it writes, the checks and the report are the CLI's, which are the site's (plugins/shared/engine/computeFins).

Tools

Tool	Writes
`fin_part`	the part + fins, posed and seated on the plate as the site exports it: `<part>-fins.3mf` beside the part, or `output` (`.3mf`, or `.stl` for one merged mesh)
`fins_only`	the fins alone as an STL, lined up with the part where it is in its file: `<part>-fins-only.stl`. Nothing is written when the part needs no fins

Both take path (an .stl or .3mf; absolute, or relative to where the server started -- which for Claude Desktop is /, so give absolute paths there; ~/ works), object for a 3MF with several objects, and settings: every setting the site has, named as the CLI's flags (coverage, tine-density, pad-style, sway, ...) in the site's units (percent sliders 0-100). The client sees the whole list, with defaults and ranges, in the tool schema. fin_part also takes rot: [x, y, z], the "X · Y · Z" readout under the part on printfins.com.

The result is the CLI's report line ("5 walls, 20 tines; 1 overhang is too shallow for a fin this way up (tilt the part steeper)") plus the numbers behind it. Unsupported overhangs are reported, not errors. A bad setting or an unreadable file is a tool error that says why, and nothing is written.

Install

Download support-fins-mcp.mjs from the plugins-latest release on GitHub. It is the whole server in one file and needs Node 20.10+ or Deno 2.

Claude Code:

claude mcp add support-fins -- node /path/to/support-fins-mcp.mjs

Claude Desktop and most other clients (claude_desktop_config.json, .mcp.json):

{
  "mcpServers": {
    "support-fins": { "command": "node", "args": ["/path/to/support-fins-mcp.mjs"] }
  }
}

With Deno instead: "command": "deno", "args": ["run", "-RWE", "/path/to/support-fins-mcp.mjs"].

CAD tools with their own MCP server

Clients can run several servers at once, so a CAD tool's own MCP server and this one can work on the same part: export the part to STL, fins_only it, import the fins back. LayerLing's server (self-hosted LayerLing only; layerling.com has it off) imports files with layerling_import_file, which takes the file's bytes, so the fins pass through the AI client on the way: fine for a small part, impractical for a big one. Not yet tried end to end. For anything else, open the 3MF from fin_part in your slicer.

Code

server.js: the protocol (JSON-RPC: initialize, tools/list, tools/call, ping) and the tools, built from the CLI's flags. No I/O of its own.
support-fins-mcp.js: stdin/stdout + the file system (Deno or Node). stdout carries only protocol lines; the engine's own logging goes to stderr.
build.py: the one-file download, build/support-fins-mcp.mjs (the CLI's bundler).
tests/server.test.js: deno test -A plugins/mcp/tests/. A tool call writes the same bytes as the CLI; the schema is the CLI's flags; errors write nothing; and a full exchange over real stdio on Deno and on Node.