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 Ed3Design/ed3design-engineering-bundles --skill mechanical-design-principlesgit clone --depth 1 https://github.com/Ed3Design/ed3design-engineering-bundlesWrote 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/ed3design/ed3design-engineering-bundles/mechanical-design-principles)<a href="https://agentmods.dev/skills/ed3design/ed3design-engineering-bundles/mechanical-design-principles"><img src="https://agentmods.dev/badge/skills/ed3design/ed3design-engineering-bundles/mechanical-design-principles/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/ed3design/ed3design-engineering-bundles/mechanical-design-principles"><img src="https://agentmods.dev/badge/skills/ed3design/ed3design-engineering-bundles/mechanical-design-principles.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 | $0.00204 | $0.05430 |
| Opus 5 | $0.00102 | $0.02715 |
| Sonnet 5 | $0.00041 | $0.01086 |
| Haiku 4.5 | $0.00020 | $0.00543 |
Grade A, and why
mechanical-design-principles 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 10d ago.
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 — 259 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Mechanical Design Principles
A design philosophy that treats every feature as a justified decision, favors elegant simplicity over accumulated complexity, and designs for manufacturability from the first sketch. FDM-focused but broadly applicable.
The foundation is two stances: form follows function (every feature earns its place by serving the mechanism) and minimum interface count (fewer parts, fewer fasteners, fewer joints wherever possible).
Read the whole skill before applying
This skill has seven core principles, supporting principles, anti-patterns, decision heuristics, and worked examples — all load-bearing. Stopping at the first few principles risks missing rules that prevent common design mistakes (e.g., Principle 4 on manufacturing, Principle 5 on parameters, the decision heuristics for tolerances). Read to the end.
Relation to other skills
- For the conversation framework (how to iterate, when to verify orientation, how to structure decisions): load
design-first-iterationalongside this skill. This skill gives the rules; design-first gives the process. - For CAD workflow (parameter tables, component decomposition, construction sequencing): use
cad-construction. That skill consumes the rules from this one and applies them in a CAD session. - For CAD automation / scripting (Python, OpenSCAD, API code): use
cad-api-scripting.
The Seven Principles
1. Form follows function — every feature earns its place
Every geometric feature must trace back to a specific functional requirement. If you cannot articulate why a feature is there — what force it carries, what tolerance it guarantees, what access it enables, what behavior it produces — then the feature is decorative at best, structural debt at worst.
Abstract rule: Before adding geometry, state the function. If the function is unclear, don't add the geometry.
FDM concrete application:
- Thickened zones should correspond to mechanical load paths (snap-fit roots, clip arms, mount interfaces), not aesthetic preferences
- Ribs and bosses belong only where stress or stiffness is needed
- Radii and fillets at stress concentrations (where two perpendicular surfaces meet under load), not merely "everywhere for the look"
- Fasciae and skirts should hide something specific (a seam, a cable path, a connector) — not be there for appearance alone
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.
- 10d ago First seen · 259 lines · 204 tokens per session scan A 563843c38d94
mechanical-design-principles is a skill published in the GitHub repository Ed3Design/ed3design-engineering-bundles (2 stars, last pushed 1mo ago), licensed MIT. It adds 204 tokens to every session and 5,430 once invoked, about $0.0010 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 2026-08-31.
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