The Ultimate Guide to HTTP Status Codes (100–599)
A complete reference guide to all HTTP status codes from 100 to 599, with explanations and common use cases.
Feb 28, 2026
5xx Server Error
11 status codes
These codes indicate that the server failed to fulfill a valid request. The error is on the server side — the server encountered an unexpected condition that prevented it from fulfilling the request.
| Code | Title | Description | RFC |
|---|---|---|---|
| 500 | Internal Server Error | The server encountered an unexpected condition that prevented it from fulfilling the request. | RFC 7231, Section 6.6.1 |
| 501 | Not Implemented | The server does not support the functionality required to fulfill the request. | RFC 7231, Section 6.6.2 |
| 502 | Bad Gateway | The server, while acting as a gateway or proxy, received an invalid response from an inbound server. | RFC 7231, Section 6.6.3 |
| 503 | Service Unavailable | The server is currently unable to handle the request due to a temporary overload or scheduled maintenance. | RFC 7231, Section 6.6.4 |
| 504 | Gateway Timeout | The server, while acting as a gateway or proxy, did not receive a timely response from an upstream server. | RFC 7231, Section 6.6.5 |
| 505 | HTTP Version Not Supported | The server does not support, or refuses to support, the major version of HTTP that was used in the request. | RFC 7231, Section 6.6.6 |
| 506 | Variant Also Negotiates | The server has an internal configuration error: the chosen variant resource is configured to engage in transparent content negotiation itself. | RFC 2295, Section 8.1 |
| 507 | Insufficient Storage | The method could not be performed on the resource because the server is unable to store the representation needed to successfully complete the request. | RFC 4918, Section 11.5 |
| 508 | Loop Detected | The server terminated an operation because it encountered an infinite loop while processing a request (WebDAV). | RFC 5842, Section 7.2 |
| 510 | Not Extended | The policy for accessing the resource has not been met in the request. | RFC 2774, Section 7 |
| 511 | Network Authentication Required | The client needs to authenticate to gain network access. | RFC 6585, Section 6 |
Last updated: 17 Aug 2026
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