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 HoangNguyen0403/agent-skills-standard --skill system-design-methodologygit clone --depth 1 https://github.com/HoangNguyen0403/agent-skills-standardWrote 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/hoangnguyen0403/agent-skills-standard/system-design-methodology)<a href="https://agentmods.dev/skills/hoangnguyen0403/agent-skills-standard/system-design-methodology"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/system-design-methodology/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/hoangnguyen0403/agent-skills-standard/system-design-methodology"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/system-design-methodology.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 | $0.00056 | $0.01403 |
| Opus 5.5 | $0.00022 | $0.00561 |
| Sonnet 5.5 | $0.00011 | $0.00281 |
| Haiku 4.5 | $0.00006 | $0.00140 |
Grade A, and why
system-design-methodology 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 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.
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 — 76 lines — stays where its author put it; the contents beside it link to each section on GitHub.
System Design Methodology
Priority: P0 (CRITICAL)
Classify work mode, depth, and system surface independently. Load only the relevant skill siblings: data-architecture for consequential data/state flows, mobile-client for mobile/client or SDK/library concerns, and diagramming only when a view is selected. Backend, mobile/client, SDK/library, and full-stack are surfaces; none is a mode.
Phase 0 - Classify
- State mode (new design | review existing | interview practice), depth (quick | full), and surface (backend | mobile/client | SDK/library | full stack). A mixed system may name multiple surfaces.
- Quick sketches use explicit assumptions and skip confirmation gates; full sessions follow the per-phase exit predicates in the four-phase process and confirm consequential decisions. Escalate quick to full for hard constraints or irreversible choices; an unresolved material decision prevents a readiness claim.
- Interview practice follows interview coaching; production review/design follows this process.
Phase 1 - Intake
- Bound questions to what changes the design. Identify journeys, inputs/outputs, actors, trust and ownership boundaries, team/budget, and scope.
- For each consequential journey, state a quality scenario: trigger, environment, response, measurable condition, and owner. Ask at most 3 blocking questions per turn; label usable defaults as
ASSUMED. - Review-existing mode maps current components, owners, traffic, incidents, and binding constraint before proposing change. SDK scope includes host responsibilities and compatibility; client scope includes authority, lifecycle, and offline need.
- See intake checklist; do not require every backend intake field for every surface.
Phase 2 - Estimation
- Estimate only quantities that shape the chosen surface and decisions. For backend/data paths, derive rates, payload/bandwidth, retention/storage, fan-out, backlog or working set as applicable. For client/device work, estimate relevant memory, disk, network, battery-sensitive work, and queue bounds. For SDKs, bound calls, concurrency, buffers, and lifecycle when material; do not force backend QPS.
- Label quantities target, estimated, or measured; state provenance and assumptions. Name the shaping quantity. Do not fabricate values or compute irrelevant metrics to fill a template.
What ships with it
4 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.
- 6d ago Changed · -24 lines · -9 tokens per session 4f58738b1a2b
- 19d ago Changed 9f5614e6f914
- 26d ago Changed · +1 lines 2d2e7d7c3642
- 1mo ago Changed · +16 lines 781f3499f9a0
- 1mo ago Changed · +2 lines · +3 tokens per session 59723d49fadb
- 1mo ago First seen · 81 lines · 62 tokens per session scan A 96b741320f37
system-design-methodology is a skill published in the GitHub repository HoangNguyen0403/agent-skills-standard (583 stars, last pushed today), licensed MIT. It adds 56 tokens to every session and 1,403 once invoked, about $0.0002 per session on Opus 5.5. 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 2026-08-30.
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