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-building-blocksgit 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-building-blocks)<a href="https://agentmods.dev/skills/hoangnguyen0403/agent-skills-standard/system-design-building-blocks"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/system-design-building-blocks/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-building-blocks"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/system-design-building-blocks.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 | $0.00061 | $0.00823 |
| Opus 5.5 | $0.00024 | $0.00329 |
| Sonnet 5.5 | $0.00012 | $0.00165 |
| Haiku 4.5 | $0.00006 | $0.00082 |
Grade A, and why
system-design-building-blocks 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.
How it starts
The opening of the file, as written. The whole thing — 73 lines — stays where its author put it; the contents beside it link to each section on GitHub.
System Building Blocks
Priority: P1 (HIGH)
Add a component only to remove a named constraint. Every component adds failure modes and cost.
Selection Table
| Constraint observed | Component | Cost accepted |
|---|---|---|
| One instance saturates CPU or connections | Horizontal scaling behind a load balancer | Statelessness required; session moves to a store |
| Read QPS exceeds store ceiling; data tolerates staleness | Read-through cache | Stale reads up to TTL; invalidation complexity |
| Write spikes exceed sustainable store throughput | Queue plus async worker | Eventual completion; needs idempotent consumers |
| Slow non-critical work blocks the request path | Background job or event | Extra delivery guarantees to reason about |
| Static or media bytes dominate egress | CDN | Cache purge lag; origin still needed for misses |
| Cross-cutting authn, quota, routing repeated per service | API gateway | Central chokepoint; must be HA |
| One tenant or key can exhaust capacity | Rate limiter or admission control | Rejections need clear client contracts |
| Cache or shard nodes change count during scaling | Consistent hashing | Rebalancing logic; hot-key skew persists |
Caching Rules
- Default to cache-aside for read-heavy paths; use write-through only when read-after-write must be exact.
- Set TTL from tolerable staleness, not from convenience. Every cached key needs a stated TTL and an invalidation trigger.
- Guard the miss path: single-flight or request coalescing prevents a stampede when a hot key expires.
- Never cache what you cannot invalidate. Never cache per-user data under a shared key.
Queue Rules
- Choose delivery semantics explicitly: at-least-once plus idempotent consumers is the safe default.
- Partition by the entity that must stay ordered; ordering is per partition, never global.
- Size the queue for the burst, and define the drain rate. An unbounded queue converts a throughput problem into a latency and memory problem.
- Apply backpressure at the producer when depth exceeds the drain budget; shedding beats silent growth.
What ships with it
2 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.
- 1mo ago First seen · 73 lines · 61 tokens per session scan A 71236855db7b
system-design-building-blocks is a skill published in the GitHub repository HoangNguyen0403/agent-skills-standard (583 stars, last pushed today), licensed MIT. It adds 61 tokens to every session and 823 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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