# HTTP Status Codes

## Success Codes (2xx)

| Code | Name | Description |
|------|------|-------------|
| 200 | OK | Standard success response |
| 201 | Created | Resource successfully created |
| 202 | Accepted | Request accepted for processing |
| 204 | No Content | Success with no body |
| 206 | Partial Content | Returning partial data |

## Redirection Codes (3xx)

| Code | Name | Description |
|------|------|-------------|
| 301 | Moved Permanently | Resource moved permanently |
| 302 | Found | Temporary redirect |
| 303 | See Other | Redirect to different URL |
| 304 | Not Modified | Use cached version |
| 307 | Temporary Redirect | Temporary redirect |
| 308 | Permanent Redirect | Permanent redirect |

## Client Error Codes (4xx)

| Code | Name | Description |
|------|------|-------------|
| 400 | Bad Request | Invalid request syntax |
| 401 | Unauthorized | Authentication required |
| 402 | Payment Required | Reserved for future use |
| 403 | Forbidden | Authenticated but not permitted |
| 404 | Not Found | Resource doesn't exist |
| 405 | Method Not Allowed | HTTP method not supported |
| 406 | Not Acceptable | Cannot produce acceptable response |
| 408 | Request Timeout | Client took too long |
| 409 | Conflict | Request conflicts with state |
| 410 | Gone | Resource permanently removed |
| 413 | Payload Too Large | Request body exceeds limit |
| 414 | URI Too Long | URL exceeds max length |
| 415 | Unsupported Media Type | Invalid content type |
| 422 | Unprocessable Entity | Validation failed |
| 429 | Too Many Requests | Rate limit exceeded |

## Server Error Codes (5xx)

| Code | Name | Description |
|------|------|-------------|
| 500 | Internal Server Error | Generic server error |
| 501 | Not Implemented | Feature not implemented |
| 502 | Bad Gateway | Invalid response from gateway |
| 503 | Service Unavailable | Server temporarily down |
| 504 | Gateway Timeout | Gateway timeout |
| 507 | Insufficient Storage | Storage limit reached |
| 511 | Network Authentication | Requires auth on network |

## Common Use Cases

### 200 OK
```json
// Standard response
{
    "data": {...}
}
```

### 201 Created
```json
// With created resource
{
    "data": {
        "id": 123,
        "name": "New Item"
    }
}
// Headers: Location: /resources/123
```

### 400 Bad Request
```json
{
    "error": {
        "code": "VALIDATION_ERROR",
        "message": "Invalid input",
        "details": [...]
    }
}
```

### 401 Unauthorized
```json
{
    "error": {
        "code": "AUTH_REQUIRED",
        "message": "Please login to continue"
    }
}
```

### 403 Forbidden
```json
{
    "error": {
        "code": "PERMISSION_DENIED",
        "message": "You don't have access to this resource"
    }
}
```

### 404 Not Found
```json
{
    "error": {
        "code": "NOT_FOUND",
        "message": "Resource not found"
    }
}
```

### 429 Too Many Requests
```json
{
    "error": {
        "code": "RATE_LIMITED",
        "message": "Too many requests",
        "retryAfter": 60
    }
}
// Headers: Retry-After: 60
```

### 500 Internal Server Error
```json
{
    "error": {
        "code": "INTERNAL_ERROR",
        "message": "Something went wrong"
    }
}
```

## Response Headers

### Standard Headers
```
Content-Type: application/json
Content-Length: 1234
Connection: keep-alive
Cache-Control: max-age=3600
```

### Rate Limiting Headers
```
X-RateLimit-Limit: 100
X-RateLimit-Remaining: 95
X-RateLimit-Reset: 1640000000
```

### Pagination Headers
```
Link: <https://api.com/users?page=2>; rel="next",
      <https://api.com/users?page=5>; rel="last"
```

## Security Best Practices

1. Never reveal internal error details in production
2. Use generic error messages for 500 errors
3. Log detailed errors server-side
4. Return appropriate status codes
5. Include error codes for client handling