Borrowing it
Nothing to install: this file belongs to andrewesweet/ropey. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/andrewesweet/ropey/main/.agents/skills/system-design/SKILL.mdgit clone --depth 1 https://github.com/andrewesweet/ropeyWrote 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/andrewesweet/ropey/system-design)<a href="https://agentmods.dev/skills/andrewesweet/ropey/system-design"><img src="https://agentmods.dev/badge/skills/andrewesweet/ropey/system-design.svg" alt="Measured on agentmods" 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 | $0.00117 | $0.03535 |
| Opus 5 | $0.00059 | $0.01767 |
| Sonnet 5 | $0.00023 | $0.00707 |
| Haiku 4.5 | $0.00012 | $0.00353 |
Grade A, and why
system-design 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 7d 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
94% identical to system-design — 29 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 — 217 lines — stays where its author put it; the contents beside it link to each section on GitHub.
System Design Framework
A structured approach to designing large-scale distributed systems. Apply these principles when architecting new services, reviewing designs, estimating capacity, or preparing for system design discussions.
Core Principle
Start with requirements, not solutions. Jumping to architecture before understanding constraints produces over- or under-engineered systems. Scalable systems are assembled from well-understood building blocks (load balancers, caches, queues, databases, CDNs) — the skill lies in choosing the right blocks, sizing them with estimates, and owning the tradeoffs each choice introduces.
Scoring
Goal: 10/10. Rate any system design 0-10: a 10/10 states requirements explicitly, includes back-of-the-envelope estimates, uses appropriate building blocks, addresses scaling and reliability, and acknowledges tradeoffs. Always state the current score and the specific improvements needed to reach 10/10.
The System Design Framework
Six areas for building reliable, scalable distributed systems:
1. The Four-Step Process
Core concept: Every design follows four stages: (1) understand the problem and establish scope, (2) propose a high-level design and get buy-in, (3) dive deep into critical components, (4) wrap up with tradeoffs and future improvements.
Why it works: Without structure, designs either stay too abstract or get lost in premature detail. The four steps invest time proportionally — broad strokes first, depth where it matters.
Key insights:
- Step 1 (~5-10 min): clarifying questions, functional and non-functional requirements, agreed scale (DAU, QPS, storage)
- Step 2 (~15-20 min): high-level diagram with APIs, services, data stores, data flow arrows
- Step 3 (~15-20 min): design the 2-3 hardest or most critical components in detail
- Step 4 (~5 min): tradeoffs, bottlenecks, future improvements
- Never skip Step 1 — ambiguous scope wastes all downstream effort; get explicit agreement on assumptions
What ships with it
6 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 7d ago First seen · 217 lines · 117 tokens per session scan A 6a51dab328e2
system-design is a skill published in the GitHub repository andrewesweet/ropey (0 stars, last pushed 2mo ago), licensed MIT. It adds 117 tokens to every session and 3,535 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. It is 94% identical to system-design, differing in 29 lines, and is treated as a copy.
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