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 RealDougEubanks/ClaudeMarketplace --skill api-designgit clone --depth 1 https://github.com/RealDougEubanks/ClaudeMarketplaceWrote 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/realdougeubanks/claudemarketplace/api-design)<a href="https://agentmods.dev/skills/realdougeubanks/claudemarketplace/api-design"><img src="https://agentmods.dev/badge/skills/realdougeubanks/claudemarketplace/api-design.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 | $0.00037 | $0.01952 |
| Opus 5 | $0.00018 | $0.00976 |
| Sonnet 5 | $0.00007 | $0.00390 |
| Haiku 4.5 | $0.00004 | $0.00195 |
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 7d 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 — 208 lines — stays where its author put it; the contents beside it link to each section on GitHub.
api-design
Purpose
Two modes:
- Design mode (
/api-design): Design a new API surface from requirements — resource modeling, endpoint naming, request/response schemas, versioning, auth, error contracts, pagination. - Review mode (
/api-design --review): Audit an existing API for consistency, best practices violations, and breaking change risks.
DESIGN MODE Instructions
Step 1 — Gather inputs
Ask the user:
- What does this API do? (domain / resource description)
- Who are the consumers? (web frontend, mobile app, third-party, internal service)
- What protocol? REST, GraphQL, gRPC, or WebSocket (or combination)
- What auth mechanism? (JWT Bearer, API Key, OAuth2, mTLS)
- Any existing APIs this must be consistent with?
Read any existing API files: openapi.yml, schema.graphql, *.proto, Swagger docs.
Step 2 — Resource Modeling (REST)
Identify the core resources from the domain description. For each resource:
- Name it as a plural noun:
/users,/orders,/products - Define its fields (name, type, required/optional, description)
- Define its relationships (belongs_to, has_many)
- Map CRUD to HTTP methods:
| Operation | Method | Path | Notes |
|---|---|---|---|
| List | GET | /resources | Supports filtering, sorting, pagination |
| Get one | GET | /resources/:id | 404 if not found |
| Create | POST | /resources | 201 + Location header on success |
| Update (full) | PUT | /resources/:id | Idempotent |
| Update (partial) | PATCH | /resources/:id | Only send changed fields |
| Delete | DELETE | /resources/:id | 204 No Content on success |
Sub-resources: use /resources/:id/sub-resources only one level deep. Deeper nesting — use query params instead.
Step 3 — Request / Response Design
For each endpoint define:
- Request: path params, query params (with types and validation), request body schema
- Response: success schema, all possible error codes and their meaning
- Side effects: what else changes when this endpoint is called
What ships with it
4 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.
- 7d ago First seen · 208 lines · 37 tokens per session scan A da63377e5a3d
api-design is a skill published in the GitHub repository RealDougEubanks/ClaudeMarketplace (1 stars, last pushed 2mo ago), licensed MIT. It adds 37 tokens to every session and 1,952 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 2026-08-31.
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