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-principlesgit 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-principles)<a href="https://agentmods.dev/skills/hoangnguyen0403/agent-skills-standard/system-design-principles"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/system-design-principles/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-principles"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/system-design-principles.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 | $0.00051 | $0.00803 |
| Opus 5.5 | $0.00020 | $0.00321 |
| Sonnet 5.5 | $0.00010 | $0.00161 |
| Haiku 4.5 | $0.00005 | $0.00080 |
Grade A, and why
system-design-principles 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 — 80 lines — stays where its author put it; the contents beside it link to each section on GitHub.
System Design Principles
Priority: P0 (CRITICAL)
Workflow: Evaluate Architecture for New Feature
- Identify bounded contexts and module boundaries
- Name the data owner and define dependency direction (outer layers depend on inner)
- Select communication pattern (sync REST, async event, or hybrid) and failure behavior
- Validate CAP trade-offs only for distributed components
- Record boundary, trade-off, and rollback in an ADR
For a failing synchronous dependency, keep the critical path explicit: timeout and circuit-break the dependency, return a defined degraded/fallback result where safe, and move non-critical notifications to an asynchronous event.
Architectural Principles
- SoC: Divide into distinct sections per concern.
- SSOT: One source, reference elsewhere.
- Fail Fast: Fail visibly when errors occur.
- Graceful Degradation: Core functional even if secondary fails.
Modularity & Coupling
- High Cohesion: Related functionality in one module.
- Loose Coupling: Use interfaces for communication.
- DI: Inject dependencies, don't hardcode.
See implementation examples for dependency flow diagrams.
Common Patterns
- Layered: Presentation -> Logic -> Data.
- Event-Driven: Async communication between decoupled components.
- Clean/Hexagonal: Core logic independent of frameworks.
- Statelessness: Favor stateless for scaling/testing.
- Monolith first: Start modular-monolith; split a service out only when a module needs independent scaling, release cadence, or ownership.
Distributed Systems
- CAP: Apply only to behavior during a network partition in a distributed data system. See CAP & Consistency Patterns; consistency, availability, and partition tolerance are not product labels or uptime percentages.
- Idempotency: Preserve one intended effect for retries of the same business operation. Use the idempotency contract, not “without side effects” or a fresh key per transport attempt.
- Circuit Breaker: Fail fast on failing services. See Resilience Patterns.
- Eventual Consistency: State a freshness/convergence objective, how it is measured, and behavior when it is missed; do not promise a generic convergence time.
What ships with it
5 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 cc23d605aa94
- 19d ago Changed 2f1fe2ed24df
- 1mo ago First seen · 80 lines · 51 tokens per session scan A f5b25c01c147
system-design-principles is a skill published in the GitHub repository HoangNguyen0403/agent-skills-standard (583 stars, last pushed today), licensed MIT. It adds 51 tokens to every session and 803 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.
Other skills, from other repositories
nextjs-app-router
Full end-to-end tRPC setup for Next.js App Router. Covers route handler with fetchRequestHandler (GET + POST exports), TRPCProvider with QueryClientProvider, createTRPCOptionsProxy for RSC prefetching, HydrateClient/HydrationBoundary for hydration, useSuspenseQuery for Suspense, and server-side callers.
nextjs-pages-router
Set up tRPC in Next.js Pages Router with createNextApiHandler, createTRPCNext, withTRPC HOC, SSR via ssr option and ssrPrepass, SSG via createServerSideHelpers with getStaticProps, and server-side helpers for getServerSideProps prefetching.
client-setup
Create a vanilla tRPC client with createTRPCClient (), configure link chain with httpBatchLink/httpLink, dynamic headers for auth, transformer on links (not client constructor). Infer types with inferRouterInputs and inferRouterOutputs. AbortController signal support. TRPCClientError typing.
links
Configure the tRPC client link chain: httpLink, httpBatchLink, httpBatchStreamLink, splitLink, loggerLink, wsLink, createWSClient, httpSubscriptionLink, unstablelocalLink, retryLink. Choose the right terminating link. Route subscriptions via splitLink. Build custom links for SOA routing. Link options: url, headers…
openapi
Generate OpenAPI 3.1 spec from a tRPC router with @trpc/openapi CLI or programmatic API. Generate typed REST client with @hey-api/openapi-ts and configureTRPCHeyApiClient(). Configure transformers (superjson, EJSON) for generated clients. Alpha status.
auth
Implement JWT/cookie authentication and authorization in tRPC using createContext for user extraction, t.middleware with opts.next({ ctx }) for context narrowing to non-null user, protectedProcedure base pattern, client-side Authorization headers via httpBatchLink headers(), WebSocket connectionParams, and SSE auth…