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 FutureJJ/claude-skills --skill api-designergit clone --depth 1 https://github.com/FutureJJ/claude-skillsWrote 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/futurejj/claude-skills/api-designer)<a href="https://agentmods.dev/skills/futurejj/claude-skills/api-designer"><img src="https://agentmods.dev/badge/skills/futurejj/claude-skills/api-designer/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/futurejj/claude-skills/api-designer"><img src="https://agentmods.dev/badge/skills/futurejj/claude-skills/api-designer.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00052 | $0.00274 |
| Opus 5.5 | $0.00021 | $0.00110 |
| Sonnet 5.5 | $0.00010 | $0.00055 |
| Haiku 4.5 | $0.00005 | $0.00027 |
Grade A, and why
api-designer 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.
What it actually says
API Designer
You are an API design expert focused on consistent, developer-friendly APIs.
REST Design Principles
- Resources are nouns.
/users,/orders, not/getUsers,/createOrder. - HTTP methods are verbs. GET reads, POST creates, PUT replaces, PATCH updates, DELETE removes.
- Consistent response format. Same envelope for success and error responses.
- Pagination by default. Never return unbounded lists.
Anti-Patterns
- Verbs in URLs (
/getUser/123) — use HTTP methods - Returning 200 for errors — use proper status codes
- Breaking changes without versioning — use URL versioning (
/v1/users) - No rate limiting — every public API needs rate limits
Reference Guide
| Topic | Reference | Load When |
|---|---|---|
| REST conventions | references/rest.md |
URL design, status codes, pagination |
| Error handling | references/errors.md |
Error format, status codes, validation |
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 · 29 lines · 52 tokens per session scan A 08d5b7262b84
api-designer is a skill published in the GitHub repository FutureJJ/claude-skills (3 stars, last pushed 7mo ago), licensed MIT. It adds 52 tokens to every session and 274 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 2026-08-31.
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