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/iwritec0de/app-dev/api-designnpx skills add iwritec0de/app-dev --skill api-designgit clone --depth 1 https://github.com/iwritec0de/app-devWhat 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 | $0.00109 | $0.01359 |
| Opus 5 | $0.00055 | $0.00679 |
| Sonnet 5 | $0.00022 | $0.00272 |
| Haiku 4.5 | $0.00011 | $0.00136 |
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 yesterday.
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 — 224 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Design Patterns
REST Resource Design
URL Structure
GET /api/v1/resources — List (with pagination)
GET /api/v1/resources/:id — Get single
POST /api/v1/resources — Create
PUT /api/v1/resources/:id — Full update
PATCH /api/v1/resources/:id — Partial update
DELETE /api/v1/resources/:id — Delete
# Nested resources
GET /api/v1/users/:id/posts — User's posts
POST /api/v1/users/:id/posts — Create post for user
# Actions (non-CRUD)
POST /api/v1/orders/:id/cancel — Action on resource
POST /api/v1/auth/login — Authentication
POST /api/v1/auth/refresh — Token refresh
Naming Rules
- Plural nouns for resources (
/users, not/user) - Kebab-case for multi-word (
/user-profiles, not/userProfiles) - No verbs in URLs (
/users, not/getUsers) - No trailing slashes
HTTP Status Codes
| Code | When to Use |
|---|---|
| 200 | Successful GET, PUT, PATCH, or DELETE |
| 201 | Successful POST (resource created). Include Location header. |
| 204 | Successful DELETE with no response body |
| 400 | Invalid request (validation error, malformed JSON) |
| 401 | Not authenticated (missing or invalid credentials) |
| 403 | Authenticated but not authorized |
| 404 | Resource not found |
| 409 | Conflict (duplicate resource, version mismatch) |
| 422 | Semantically invalid (valid JSON, but business logic rejects it) |
| 429 | Rate limit exceeded. Include Retry-After header. |
| 500 | Server error (never expose internals) |
Response Formats
Success (Direct)
{
"id": "uuid",
"name": "Example",
"createdAt": "2025-01-01T00:00:00Z"
}
Success (Envelope)
{
"data": { ... },
"meta": {
"page": 1,
"perPage": 20,
"total": 150
}
}
Error
{
"error": {
"code": "VALIDATION_ERROR",
"message": "Invalid request body",
"details": [
{
"field": "email",
"message": "Must be a valid email address"
}
]
}
}
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.
- yesterday First seen · 224 lines · 109 tokens per session scan A ab9671bcfce4
api-design is a skill published in the GitHub repository iwritec0de/app-dev (3 stars, last pushed 4mo ago), licensed MIT. It adds 109 tokens to every session and 1,359 once invoked, about $0.0005 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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