api-design

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• SKILL.md

SKILL.md (first lines)

# API Design Guide

Best practices for designing developer-friendly, maintainable APIs.

## REST API Principles

### Resource Naming

**Use nouns, not verbs**:

```
✓ GET /users
✓ GET /users/123
✓ GET /users/123/orders

✗ GET /getUsers
✗ GET /fetchUserById
✗ POST /createNewOrder
```

**Use plural nouns**:

```
✓ /users
✓ /orders
✓ /products

✗ /user
✗ /order
```

**Hierarchical relationships**:

```
/users/{userId}/orders           # User's orders
/users/{userId}/orders/{orderId} # Specific order
```

---

### HTTP Methods

| Method | Purpose                   | Idempotent | Request Body |
| ------ | ------------------------- | ---------- | ------------ |
| GET    | Retrieve resource(s)      | Yes        | No           |
| POST   | Create resource           | No         | Yes          |
| PUT    | Replace resource entirely | Yes        | Yes          |
| PATCH  | Update resource partially | No         | Yes          |
| DELETE | Remove resource           | Yes        | No           |

---

### Status Codes

**Success (2xx)**:

- `200 OK` - Request succeeded
- `201 Created` - Resource created (return Location header)
- `204 No Content` - Success with no response body

**Client Error (4xx)**:

- `400 Bad Request` - Malformed request
- `401 Unauthorized` - Authentication required
- `403 Forbidden` - No permission
- `404 Not Found` - Resource doesn't exist
- `409 Conflict` - State conflict
- `422 Unprocessable Entity` - Validation failed
- `429 Too Many Requests` - Rate limited

**Server Error (5xx)**:

- `500 Internal Server Error` - Unexpected error
- `503 Service Unavailable` - Temporary outage

---

### Response Format

**Successful response**:

```json
{
  "data": {
    "id": "123",
    "name": "John Doe",
    "email": "john@example.com"
  }
}
```

**Collection response**:

```json
{
  "data": [
    { "id": "1", "name": "Item 1" },
    { "id": "2", "name": "Item 2" }
  ],
  "meta": {
    "page": 1,
    "perPage": 20,
    "total": 100,
    "totalPages": 5
  },
  "links": {
    "self": "/items?page=1",
    "next": "/items?page=2",
    "prev": null
  }
}
```

**Error response**:

```json
{
  "error": {
    "code": "VALIDATION_ERROR",

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