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/oborchers/fractional-cto/using-api-principlesnpx skills add oborchers/fractional-cto --skill using-api-principlesgit clone --depth 1 https://github.com/oborchers/fractional-ctoWrote 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/oborchers/fractional-cto/using-api-principles)<a href="https://agentmods.dev/skills/oborchers/fractional-cto/using-api-principles"><img src="https://agentmods.dev/badge/skills/oborchers/fractional-cto/using-api-principles.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 | $0.00073 | $0.00889 |
| Opus 5 | $0.00036 | $0.00445 |
| Sonnet 5 | $0.00015 | $0.00178 |
| Haiku 4.5 | $0.00007 | $0.00089 |
Grade A, and why
using-api-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 — 54 lines — stays where its author put it; the contents beside it link to each section on GitHub.
These are not suggestions. They are research-backed, opinionated principles drawn from Stripe, GitHub, Twilio, Shopify, Google, Microsoft, Zalando, Cloudflare, OWASP, and industry RFCs.
How to Access Skills
Use the Skill tool to invoke any skill by name. When invoked, follow the skill's guidance directly.
Available Skills
| Skill | Triggers On |
|---|---|
api-design-principles:routes-and-naming |
URL design, endpoint naming, plural nouns, nesting depth, query vs path params, snake_case, field naming |
api-design-principles:http-methods |
GET/POST/PUT/PATCH/DELETE semantics, idempotency per verb, CRUD operations, method selection |
api-design-principles:prefixed-ids |
Type-safe identifiers, Stripe-style prefixed IDs (cus_, ord_), KSUID, ULID, ID generation |
api-design-principles:errors-and-status-codes |
HTTP status codes, error envelopes, per-field validation errors, RFC 9457, error formatting |
api-design-principles:response-design-and-pagination |
Response envelopes, cursor/offset/keyset pagination, expand patterns, list metadata |
api-design-principles:auth-and-api-keys |
API key design (sk_live_, pk_test_), OAuth 2.0, JWT, Bearer tokens, key rotation |
api-design-principles:rate-limiting-and-security |
Rate limiting algorithms/headers, OWASP API Top 10, CORS, input validation, request signing |
api-design-principles:versioning-and-evolution |
URL versioning (/v1/), date-based versioning, sunset headers, additive evolution, deprecation |
api-design-principles:caching-and-performance |
Cache-Control, ETags, conditional requests, CDN strategies, compression, circuit breakers |
api-design-principles:webhooks-and-events |
HMAC-SHA256 signing, retry logic, event naming (resource.action), webhook endpoints |
api-design-principles:documentation-and-dx |
API docs, interactive explorers, SDK generation, onboarding, time-to-first-call, changelogs |
api-design-principles:advanced-patterns |
Bulk/batch ops, REST vs GraphQL vs gRPC, SSE/WebSockets, multi-tenancy, API gateways, CQRS |
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 · 54 lines · 73 tokens per session scan A 1449646e6d37
using-api-principles is a skill published in the GitHub repository oborchers/fractional-cto (29 stars, last pushed 1mo ago), licensed MIT. It adds 73 tokens to every session and 889 once invoked, about $0.0004 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 2026-08-30.
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