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 common-api-designgit 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/common-api-design)<a href="https://agentmods.dev/skills/hoangnguyen0403/agent-skills-standard/common-api-design"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/common-api-design/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/common-api-design"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/common-api-design.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 | $0.00046 | $0.00895 |
| Opus 5 | $0.00023 | $0.00447 |
| Sonnet 5 | $0.00009 | $0.00179 |
| Haiku 4.5 | $0.00005 | $0.00089 |
Grade A, and why
common-api-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 9d 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 — 90 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Common API Design Standards
Priority: P1 (HIGH)
🔧 HTTP Verb Semantics
GETread-only, idempotent — never mutates state.POSTcreate or trigger;PUTfull replace;PATCHpartial update;DELETEremove.- Non-CRUD actions as sub-resources:
POST /orders/:id/cancel.
📡 Status Code Correctness
200success;201created (addLocationheader);204no body.400validation (withdetails[]);401unauthenticated;403unauthorized;404not found.409conflict;422business rule violation;429rate limit (addRetry-After);500unhandled.
📦 URL Design Rules
- Lowercase, kebab-case:
/user-profiles, not/UserProfilesor/user_profiles. - Plural nouns:
/orders,/products. Not/order,/getProducts. - No verbs in paths (except action sub-resources):
/orders/:id/cancel✅,/cancelOrder❌. - Hierarchy: Use nesting only up to 2 levels:
/users/:id/orders✅,/users/:id/orders/:orderId/items/:itemId❌.
🔢 API Versioning
- Strategy: URL path versioning default:
/v1/users,/v2/users. - Header versioning (
Api-Version: 2) acceptable for internal APIs. - Never mix versions in same controller — each version gets its own route module.
- Support prev major ≥ 6 months after new release.
- Deprecation:
Deprecation: true+Sunset: <date>headers when version will be retired.
📄 Pagination
- Prefer cursor-based (
cursor+limit) for large/live datasets; offset only for small static ones. - Default
limit: 20, max100. Reject requests exceeding max. - Response envelope:
{ data: [], pagination: { nextCursor, hasNextPage } }.
📝 OpenAPI Contract
- Generate from code annotations — not hand-written YAML.
- Every API needs OpenAPI 3.1 spec.
- Include: request/response schemas, error shapes, auth requirements, examples.
- Review spec in PR — breaking changes need version bump.
🔒 API Security Baseline
- Require auth on all routes by default; use
@Public()or equivalent opt-out. - Validate and sanitize all query params, path params, and request bodies.
- Set
Content-Type: application/jsonexplicitly. Reject unexpected content types. - Include
X-Content-Type-Options: nosniffandX-Frame-Options: DENYheaders.
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.
- 9d ago First seen · 90 lines · 46 tokens per session scan A cd1c5613f01a
common-api-design is a skill published in the GitHub repository HoangNguyen0403/agent-skills-standard (565 stars, last pushed 3d ago), licensed MIT. It adds 46 tokens to every session and 895 once invoked, about $0.0002 per session on Opus 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 2026-09-03.
Other skills, from other repositories
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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.
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.
server-setup
Initialize tRPC with initTRPC.create(), define routers with t.router(), create procedures with .query()/.mutation()/.subscription(), configure context with createContext(), export AppRouter type, merge routers with t.mergeRouters(), lazy-load routers with lazy().
subscriptions
Set up real-time event streams with async generator subscriptions using .subscription(async function() { yield }). SSE via httpSubscriptionLink is recommended over WebSocket. Use tracked(id, data) from @trpc/server for reconnection recovery with lastEventId. WebSocket via wsLink and createWSClient from @trpc/client…
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.