| 500 | Internal server error | Light · Dark |
| 501 | Not implemented | Light · Dark |
| 502 | Bad gateway | Light · Dark |
| 503 | Service unavailable | Light · Dark |
| 504 | Gateway timeout | Light · Dark |
| 505 | HTTP version not supported | Light · Dark |
| 506 | Variant also negotiates | Light · Dark |
| 507 | Insufficient storage | Light · Dark |
| 508 | Loop detected | Light · Dark |
| 510 | Not extended | Light · Dark |
| 511 | Network authentication required | Light · Dark |
| 520 | Unknown server response | Light · Dark |
| 521 | Server connection refused | Light · Dark |
| 522 | Connection timed out | Light · Dark |
| 523 | Origin unreachable | Light · Dark |
| 524 | Server response timed out | Light · Dark |
| 525 | Secure connection failed | Light · Dark |
| 526 | Invalid server certificate | Light · Dark |
| 527 | Railgun connection error | Light · Dark |
| 530 | Origin hostname resolution failed | Light · Dark |