74-api-design

Rules for designing and using web APIs, including HTTP method choices, URL naming, response formats, status codes, validation, rate limits, request tracing, and API documentation.

In plain words
What is it for?
Use them when creating API endpoints, consuming external APIs, defining routes and response shapes, validating inputs, choosing status codes, or documenting an API.
Why use it?
They provide consistent decisions for how clients send requests and receive success or error responses. This reduces confusing endpoints, inconsistent errors, and avoidable security or maintenance problems.

Cursor rule for Cursor

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 rules/zoxknez/ai-coding-rules/74-api-design
Clone the repo
git clone --depth 1 https://github.com/zoxknez/ai-coding-rules

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 345 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 $0.00000 $0.00345
Opus 5 $0.00000 $0.00172
Sonnet 5 $0.00000 $0.00069
Haiku 4.5 $0.00000 $0.00034

Measured 2d ago against content hash ab46bc58c363, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

74-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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

.cursor/rules/74-api-design.mdc · 59 lines

What it actually says

API Design Rules

RESTful Conventions

  • GET: Retrieve resources (idempotent)
  • POST: Create resources
  • PUT: Replace resources (idempotent)
  • PATCH: Partial update
  • DELETE: Remove resources (idempotent)

URL Design

  • Use nouns for resources: /users, /orders
  • Use hyphens for readability: /order-items
  • Nest for relationships: /users/:id/orders
  • Version your API: /v1/users

Request/Response

// Consistent error shape
interface ApiError {
  code: string;        // "USER_NOT_FOUND"
  message: string;     // User-friendly message
  details?: unknown;   // Additional context
}

// Paginated response
interface PaginatedResponse<T> {
  data: T[];
  meta: {
    total: number;
    page: number;
    limit: number;
  };
}

Status Codes

  • 200: Success
  • 201: Created
  • 204: No Content (DELETE)
  • 400: Bad Request (validation)
  • 401: Unauthorized (authn)
  • 403: Forbidden (authz)
  • 404: Not Found
  • 422: Unprocessable Entity
  • 500: Internal Server Error

Best Practices

  • Validate inputs at the boundary
  • Use rate limiting
  • Add request IDs for tracing
  • Document with OpenAPI/Swagger
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 · 59 lines · 0 tokens per session scan A ab46bc58c363

Subscribe to this mod's changes

74-api-design is a cursor rule published in the GitHub repository zoxknez/ai-coding-rules (27 stars, last pushed 4mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 345 tokens. 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.