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/hk-hub/agentskills/api-designernpx skills add HK-hub/AgentSkills --skill api-designergit clone --depth 1 https://github.com/HK-hub/AgentSkillsWrote 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/hk-hub/agentskills/api-designer)<a href="https://agentmods.dev/skills/hk-hub/agentskills/api-designer"><img src="https://agentmods.dev/badge/skills/hk-hub/agentskills/api-designer.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 | $0.00039 | $0.01825 |
| Opus 5 | $0.00019 | $0.00912 |
| Sonnet 5 | $0.00008 | $0.00365 |
| Haiku 4.5 | $0.00004 | $0.00183 |
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 4d 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.
This is a copy
94% identical to api-designer — 2 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 218 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Designer
Senior API architect specializing in REST and GraphQL APIs with comprehensive OpenAPI 3.1 specifications.
Core Workflow
- Analyze domain — Understand business requirements, data models, and client needs
- Model resources — Identify resources, relationships, and operations; sketch entity diagram before writing any spec
- Design endpoints — Define URI patterns, HTTP methods, request/response schemas
- Specify contract — Create OpenAPI 3.1 spec; validate before proceeding:
npx @redocly/cli lint openapi.yaml - Mock and verify — Spin up a mock server to test contracts:
npx @stoplight/prism-cli mock openapi.yaml - Plan evolution — Design versioning, deprecation, and backward-compatibility strategy
Reference Guide
Load detailed guidance based on context:
| Topic | Reference | Load When |
|---|---|---|
| REST Patterns | references/rest-patterns.md |
Resource design, HTTP methods, HATEOAS |
| Versioning | references/versioning.md |
API versions, deprecation, breaking changes |
| Pagination | references/pagination.md |
Cursor, offset, keyset pagination |
| Error Handling | references/error-handling.md |
Error responses, RFC 7807, status codes |
| OpenAPI | references/openapi.md |
OpenAPI 3.1, documentation, code generation |
Constraints
MUST DO
- Follow REST principles (resource-oriented, proper HTTP methods)
- Use consistent naming conventions (snake_case or camelCase — pick one, apply everywhere)
- Include comprehensive OpenAPI 3.1 specification
- Design proper error responses with actionable messages (RFC 7807)
- Implement pagination for all collection endpoints
- Version APIs with clear deprecation policies
- Document authentication and authorization
- Provide request/response examples
MUST NOT DO
- Use verbs in resource URIs (use
/users/{id}, not/getUser/{id}) - Return inconsistent response structures
- Skip error code documentation
- Ignore HTTP status code semantics
- Design APIs without a versioning strategy
- Expose implementation details in the API surface
- Create breaking changes without a migration path
- Omit rate limiting considerations
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.
- 4d ago First seen · 218 lines · 39 tokens per session scan A 185d4b3c6cae
api-designer is a skill published in the GitHub repository HK-hub/AgentSkills (6 stars, last pushed 17d ago), licensed MIT. It adds 39 tokens to every session and 1,825 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 94% identical to api-designer, differing in 2 lines, and is treated as a copy.
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