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 byerlikaya/claude-starter-kit --skill api-designgit clone --depth 1 https://github.com/byerlikaya/claude-starter-kitWrote 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/byerlikaya/claude-starter-kit/api-design)<a href="https://agentmods.dev/skills/byerlikaya/claude-starter-kit/api-design"><img src="https://agentmods.dev/badge/skills/byerlikaya/claude-starter-kit/api-design.svg" alt="Measured on agentmods" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Prompt Injection · line 10 Hidden instructions were detected in comments or invisible text. These could contain malicious directives. Manual review is recommended.Fix: Audit all comments and invisible characters. Remove any instructions that direct the agent to perform unauthorized actions. Use plain, reviewable content.
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 | $0.00033 | $0.00821 |
| Opus 5 | $0.00016 | $0.00411 |
| Sonnet 5 | $0.00007 | $0.00164 |
| Haiku 4.5 | $0.00003 | $0.00082 |
Grade A, and why
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 8d 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 — 53 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Design
Trigger phrases: "api design", "api contract", "api versioning", "openapi", "swagger", "rest contract", "breaking api change", "response shape", "response format", "endpoint returns", "error format"
Goal: a contract the consumer can predict and that can evolve without breaking. Once published, a public API is a commitment; a breaking change is expensive. Stack-agnostic (REST as the baseline; GraphQL/gRPC follow similar principles).
Checklist
- Resource names are consistent (plural nouns, a single
kebab/camelstyle), resources not verbs - Correct HTTP semantics: GET (side-effect free) · POST · PUT/PATCH · DELETE; correct status code
- A uniform error model: machine-readable code + human message + (if any) field details
- A clear versioning strategy (URL
/v1or header); a breaking change means a new version - Pagination/filtering/sorting defined and consistent on large collections
- Backward compatibility: adding a field is additive; removing a field or changing its meaning is breaking → version
- Idempotency (for POST/payment-like cases) supported via a key when needed
- The contract is documented in OpenAPI; example request/response present (coordinate with
docs-writer)
How
- Model the resource — a noun not a verb:
POST /orders(✓),POST /createOrder(✗). - Status codes: 200/201/204 · 400 validation · 401/403 authorization · 404 · 409 conflict · 422 · 429 · 5xx. Use them meaningfully.
- Error contract — every error has the same shape:
No stack trace / internal detail leakage (overlaps with{ "code": "ORDER_NOT_FOUND", "message": "Order not found", "details": [] }security-scan). - Versioning: additive changes in the same version; breaking (remove/rename a field / add a required field) →
/v2. - Collection: pagination (cursor or offset), filter/sort parameters; a consistent envelope.
- Write the contract — OpenAPI/schema; with examples. Wire the change to
docs-writer, and if breaking torelease/CHANGELOG.
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.
- 8d ago First seen · 53 lines · 33 tokens per session scan A 075a407e3290
api-design is a skill published in the GitHub repository byerlikaya/claude-starter-kit (22 stars, last pushed yesterday), licensed MIT. It adds 33 tokens to every session and 821 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 2026-08-30.
Other skills, from other repositories
authentication-patterns
OAuth 2.0, JWT, SSO, MFA, NextAuth/Clerk/Supabase Auth implementation patterns.
email-systems
Transactional email (Resend, SendGrid, SES), templates (React Email, MJML), deliverability (SPF/DKIM/DMARC), and inboxing best practices. Use when building email infrastructure, designing templates, or troubleshooting deliverability.
event-driven-architecture
Kafka, RabbitMQ, SQS/SNS, event sourcing, CQRS, saga patterns, dead letter queues, and idempotency. Use when designing asynchronous systems, implementing message-driven workflows, or building event streaming pipelines.
graphql-expert
GraphQL API design and implementation. Use when building GraphQL APIs, designing schemas, implementing resolvers, or optimizing GraphQL performance.
api-design
REST and GraphQL API design best practices including OpenAPI specs. Use when designing APIs, documenting endpoints, or reviewing API architecture.
generic-fullstack-feature-developer
Guide feature development for full-stack applications with architecture focus. Covers Next.js App Router patterns, NestJS backend services, database models, data workflows, and seamless integration. Use when adding new features, refactoring existing code, or planning major changes.