api-design

A set of conventions for designing REST APIs, which are web interfaces that let programs access and change resources through HTTP requests.

In plain words
What is it for?
Use it when creating or reviewing API endpoints, adding resources, choosing HTTP responses, or planning changes that must remain compatible.
Why use it?
It makes endpoints, status codes, pagination, filtering, versioning, and errors consistent and easier for clients to use.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/dvnghiem/flowdeck/api-design
Any agent
npx skills add DVNghiem/FlowDeck --skill api-design
Clone the repo
git clone --depth 1 https://github.com/DVNghiem/FlowDeck

Made for: Claude Code, Codex.

Per session 33 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 900 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00033 $0.00900
Opus 5 $0.00016 $0.00450
Sonnet 5 $0.00007 $0.00180
Haiku 4.5 $0.00003 $0.00090

Measured 2d ago against content hash 8e557905b2ac, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

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 2d 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.

src/skills/api-design/SKILL.md · 149 lines

How it starts

The opening of the file, as written. The whole thing — 149 lines — stays where its author put it; the contents beside it link to each section on GitHub.

API Design Skill

REST API design patterns. Consistent, predictable, and easy to use.

When to Activate

Activate when:

  • Designing new API endpoints
  • Reviewing existing API for inconsistencies
  • Adding a new resource to an existing API
  • Evaluating an external API design

Core Principles

  • Nouns, not verbs in URLs — resources, not actions
  • Consistent naming — same conventions throughout
  • Standard status codes — use what HTTP intended
  • No breaking changes without versioning

Resource Design

✅ Good:
GET    /api/v1/users           — list users
GET    /api/v1/users/:id       — get user by ID
POST   /api/v1/users           — create user
PUT    /api/v1/users/:id       — replace user
PATCH  /api/v1/users/:id       — update user fields
DELETE /api/v1/users/:id       — delete user

❌ Bad:
GET  /getUsers
POST /createUser
GET  /deleteUser?id=123

HTTP Methods and Status Codes

Method Success Code Use For
GET 200 OK Retrieve resource(s)
POST 201 Created Create new resource
PUT 200 OK Replace entire resource
PATCH 200 OK Update specific fields
DELETE 204 No Content Delete resource

Error codes:

Code Meaning
400 Bad Request — malformed request body
401 Unauthorized — missing or invalid auth token
403 Forbidden — authenticated but not authorized
404 Not Found — resource does not exist
409 Conflict — duplicate resource
422 Unprocessable — valid format, failed validation
429 Too Many Requests — rate limit exceeded
500 Internal Server Error — unexpected server failure

Error Response Format

All errors use this standard shape:

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Email address is invalid",
    "details": [
      { "field": "email", "message": "Must be a valid email address" }
    ]
  }
}

Pagination

Offset-based (simple, but slow on large datasets):

GET /api/v1/users?page=2&limit=20

Response:
{
  "data": [...],
  "pagination": {
    "page": 2,
    "limit": 20,
    "total": 847,
    "pages": 43
  }
}

Read the full file on GitHub · 149 lines

Changes

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.

  1. 2d ago First seen · 149 lines · 33 tokens per session scan A 8e557905b2ac

Subscribe to this mod's changes

api-design is a skill published in the GitHub repository DVNghiem/FlowDeck (24 stars, last pushed 14d ago), licensed MIT. It adds 33 tokens to every session and 900 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.

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