Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add Fluid-CAD/FluidCAD --skill fluidcad-assemblygit clone --depth 1 https://github.com/Fluid-CAD/FluidCADWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/fluid-cad/fluidcad/fluidcad-assembly)<a href="https://agentmods.dev/skills/fluid-cad/fluidcad/fluidcad-assembly"><img src="https://agentmods.dev/badge/skills/fluid-cad/fluidcad/fluidcad-assembly/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/fluid-cad/fluidcad/fluidcad-assembly"><img src="https://agentmods.dev/badge/skills/fluid-cad/fluidcad/fluidcad-assembly.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00154 | $0.04717 |
| Opus 5 | $0.00077 | $0.02358 |
| Sonnet 5 | $0.00031 | $0.00943 |
| Haiku 4.5 | $0.00015 | $0.00472 |
Grade A, and why
FluidCAD-assembly scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured today.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 203 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Provenance: maintained in the FluidCAD repo (https://github.com/Fluid-CAD/FluidCAD), under mcp/skills/. The installed local skill files are the runtime source of truth.
Assemblies in FluidCAD
This skill layers on top of the FluidCAD skill. That one owns the loop: read the docs, plan in generic CAD terms, build in increments, check render.state and objectErrors, resolve filters before writing them, screenshot when a feature earns it, roll back to debug, and report only what was checked. Follow it for every part. This skill covers only what is specific to models made of several parts: when to split, how a part publishes its interface, how an assembly places and joins instances, and how to verify the result.
The governing principle: a part is verified alone before it is inserted, and mates are added one at a time. An assembly is where three parts' mistakes meet; keep the mistakes out of it.
1. When to split a model into parts
Split when the pieces are separate physical components: things fabricated separately, bought (a bolt, a bearing, a rail), moving relative to each other (a lever on a pin, a carriage on a rail), or reused with different parameters (four standoffs of two heights). Features of one machined or printed body (holes, ribs, fillets) are never parts.
Two rules from the API decide the mechanics:
- Inside a
part(), shapes auto-fuse with each other and never with anything outside it. Two solids that touch but must stay separate go in two parts. Inside one part,.new()keeps a feature as a separate body. - Only an exported
part()can be inserted. A standalone model needs nopart()at all.
Convention: one part per .part.js file, named after the thing it is (bracket.part.js exports bracket); one .assembly.js file per mechanism. Several components in one file each get their own part(), but that file cannot be inserted piecemeal with the same clarity, so prefer one file each.
2. Files and units
| suffix | scene | contents |
|---|---|---|
.part.js |
part | modelling statements; export const x = part("X", () => { … }) when an assembly will insert it |
.assembly.js |
assembly | export const x = assembly("x", () => { insert(); mate(); … }) |
.fluid.js |
part | legacy suffix, same as .part.js |
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- today First seen · 203 lines · 0 tokens per session scan A 167273c47343
FluidCAD-assembly is a skill published in the GitHub repository Fluid-CAD/FluidCAD (533 stars, last pushed today), licensed MIT. It adds 154 tokens to every session and 4,717 once invoked, about $0.0008 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-12.
Other skills, from other repositories
cad-viewer
Start CAD Viewer and return review links for CAD and robot-description files. Use when visually reviewing .step, .stp, .glb, .stl, .3mf, .dxf, .urdf, .srdf, or .sdf files, especially when handed off from CAD, URDF, SRDF, or SDF generation skills.
add-interfaces
Enrich an existing PartCAD part with connection interfaces and ports (mating metadata) so it can be mated to other parts automatically. Use for /pc:add-interfaces or when the user asks to add interfaces, ports, connectors, or mating information to a part, or to make parts snap/connect/assemble together.
gen-assembly
Generate a PartCAD assembly (an ASSY that composes parts with placement and/or mates) from a description, generating or reusing the component parts and validating the result with the PartCAD CLI. Use for /pc:gen-assembly or when the user asks to generate or create an assembly, mechanism, or multi-part product.
render
Render a PartCAD object or a CAD file to a 2D image - PNG, JPEG, SVG or DXF - from one or many viewing angles (front, back, left, right, top, bottom, iso, or an arbitrary direction), with pc render for an object a package declares or pc adhoc render for a file that belongs to no package. Use for /pc:render or when the…
gen-part
Generate a PartCAD part from a natural-language description (and optional reference images/requirements) by authoring a CAD script and validating it with the PartCAD CLI. Use for /pc:gen-part or when the user asks to generate, create, or model a single mechanical part.
gen-sketch
Generate a PartCAD 2D sketch from a natural-language description by authoring the sketch (build123d / cadquery / dxf / svg / basic) and validating it with the PartCAD CLI. Use for /pc:gen-sketch or when the user asks to generate, create, or draw a 2D sketch, profile, outline, or blueprint.