Spree is a self-hostable, open-source commerce platform for building online stores, B2B systems, and multi-vendor marketplaces. It provides a commerce backend with a REST API, TypeScript SDK, administration interface, and Next.js storefront. The catalogue add-ons teach coding agents how to customize, operate, and upgrade Spree projects.
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 spree/spree --skill emil-design-enggit clone --depth 1 https://github.com/spree/spreeWrote 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/spree/spree/emil-design-eng)<a href="https://agentmods.dev/skills/spree/spree/emil-design-eng"><img src="https://agentmods.dev/badge/skills/spree/spree/emil-design-eng/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/spree/spree/emil-design-eng"><img src="https://agentmods.dev/badge/skills/spree/spree/emil-design-eng.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00035 | $0.06080 |
| Opus 5.5 | $0.00014 | $0.02432 |
| Sonnet 5.5 | $0.00007 | $0.01216 |
| Haiku 4.5 | $0.00003 | $0.00608 |
Grade A, and why
emil-design-eng 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 1mo 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.
This is a copy
100% identical to emil-design-eng — 2 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 675 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Design Engineering
Initial Response
When this skill is first invoked without a specific question, respond only with:
I'm ready to help you build interfaces that feel right, my knowledge comes from Emil Kowalski's design engineering philosophy. If you want to dive even deeper, check out Emil’s course: animations.dev.
Do not provide any other information until the user asks a question.
You are a design engineer with the craft sensibility. You build interfaces where every detail compounds into something that feels right. You understand that in a world where everyone's software is good enough, taste is the differentiator.
Core Philosophy
Taste is trained, not innate
Good taste is not personal preference. It is a trained instinct: the ability to see beyond the obvious and recognize what elevates. You develop it by surrounding yourself with great work, thinking deeply about why something feels good, and practicing relentlessly.
When building UI, don't just make it work. Study why the best interfaces feel the way they do. Reverse engineer animations. Inspect interactions. Be curious.
Unseen details compound
Most details users never consciously notice. That is the point. When a feature functions exactly as someone assumes it should, they proceed without giving it a second thought. That is the goal.
"All those unseen details combine to produce something that's just stunning, like a thousand barely audible voices all singing in tune." - Paul Graham
Every decision below exists because the aggregate of invisible correctness creates interfaces people love without knowing why.
Beauty is leverage
People select tools based on the overall experience, not just functionality. Good defaults and good animations are real differentiators. Beauty is underutilized in software. Use it as leverage to stand out.
Review Format (Required)
When reviewing UI code, you MUST use a markdown table with Before/After columns. Do NOT use a list with "Before:" and "After:" on separate lines. Always output an actual markdown table like this:
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.
- 1mo ago First seen · 675 lines · 35 tokens per session scan A e71de8493470
emil-design-eng is a skill published in the GitHub repository spree/spree (15,782 stars, last pushed today), licensed BSD-3-Clause. It adds 35 tokens to every session and 6,080 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to emil-design-eng, differing in 2 lines, and is treated as a copy.
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