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 agentmods add skills/pinchen147/system-design-skill/system-designnpx skills add pinchen147/system-design-skill --skill system-designgit clone --depth 1 https://github.com/pinchen147/system-design-skillWrote 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/pinchen147/system-design-skill/system-design)<a href="https://agentmods.dev/skills/pinchen147/system-design-skill/system-design"><img src="https://agentmods.dev/badge/skills/pinchen147/system-design-skill/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 | $0.00174 | $0.03712 |
| Opus 5 | $0.00087 | $0.01856 |
| Sonnet 5 | $0.00035 | $0.00742 |
| Haiku 4.5 | $0.00017 | $0.00371 |
Grade C, and why
system-design scanned grade C with 2 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 6d 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.
Reads agent configuration directoriesmediumAgent snooping
.claude/, .codex/, .gemini/ hold keys, settings and other credentials a mod has no legitimate need for.
If the skill directory is not known, find it rather than skipping the step: `ls ~/.claude/skills/system-design/scripts/render_report.py ~/.agents/skills/system-design/scripts/render_report.py 2>/dev/null` covers both sta Enumerates other installed skillsmediumAgent snooping
Other skills' SKILL.md files reveal prompts, capabilities and secrets that should be invisible to peers.
If the skill directory is not known, find it rather than skipping the step: `ls ~/.claude/skills/system-design/scripts/render_report.py ~/.agents/skills/system-design/scripts/render_report.py 2>/dev/null` covers both sta How it starts
The opening of the file, as written. The whole thing — 154 lines — stays where its author put it; the contents beside it link to each section on GitHub.
System Design
Architecture is decided by invariants, workload numbers, failure modes, and operating constraints—not vibes. Draw the simplest production-viable candidate first, add only evidence-surviving alternatives that differ on a load-bearing axis, recommend one with an evidence chain, and leave a design artifact another coding-agent session can continue.
The process is identical in repository and greenfield work; interview-grade reasoning falls out of production discipline.
Every recommendation must cite an envelope number, a correctness invariant, a named failure mode, or a principle from HEURISTICS.md.
Do not load examples by default. Only if a first-draft recommendation or interface remains generic, consult the matching BAD/GOOD contrast in EXAMPLES.md, then replace generic language with the relevant number, invariant, ownership boundary, or failure behavior.
Process
0. Size the ask before running the process
This process earns its cost when a decision is hard to reverse, the numbers are load-bearing, or several structurally different designs are genuinely live. Sketch the envelope first. If it lands below the anti-overengineering gates in HEURISTICS.md, or one recorded decision already forces the answer, say which gate or decision closed it and answer directly in a paragraph—no artifacts. A false choice rendered as peer tabs is worse than no document.
When the process does run, draw the simplest production-viable design first. Add a candidate only when it remains viable after the envelope and invariants and changes a load-bearing axis—for example, the measured scale boundary or the dominant correctness, failure-isolation, cost, or operability risk. Record options closed by a requirement, gate, or named failure as one-line rejections; do not draw, rate, or audit them as peers. Three candidates is the ceiling, not a target.
1. Locate and resume
List existing designs—docs/design/*/design.json, or ./*/design.json outside a git repo—and read each one's slug, title, and status. If one covers this ask, load it and apply the user's feedback before doing new discovery; if two could, name both and ask which.
What ships with it
15 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.
- agents/openai.yaml 199 B
- ARCHETYPES.md 3.7 KB
- archetypes/authoritative-state.md 11 KB
- archetypes/control-security.md 13 KB
- archetypes/data-delivery.md 5.1 KB
- archetypes/derived-serving.md 13 KB
- archetypes/realtime-sync.md 7.0 KB
- archetypes/traffic-work.md 10 KB
- assets/report-template.html 105 KB
- AUDIT.md 32 KB
- EXAMPLES.md 3.3 KB
- HEURISTICS.md 24 KB
- HTML-REPORT.md 30 KB
- INTERVIEW.md 9.6 KB
- scripts/render_report.py 4.7 KB runs code
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.
- 6d ago First seen · 154 lines · 174 tokens per session scan C a5a0e9eb2bf8
system-design is a skill published in the GitHub repository pinchen147/system-design-skill (22 stars, last pushed 25d ago), licensed MIT. It adds 174 tokens to every session and 3,712 once invoked, about $0.0009 per session on Opus 5. A static security scan graded it C with 2 findings (reads agent configuration directories, enumerates other installed skills). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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