---
title: "501 Not Implemented — what it means and how to fix it"
description: "The server does not support the functionality needed to fulfil the request, usually the HTTP method itself. What causes an HTTP 501, what to try as a visitor, and what to check if it is your own site."
url: https://atoneplace.net/error/501/
site: "At One Place"
---

# HTTP 501 — Not Implemented

**HTTP 501: Not Implemented**

The server does not support the functionality needed to fulfil the request, usually the HTTP method itself.

## What 501 actually means

The server does not recognise the request method at all, or cannot support it for any resource. This is broader than 405: a 405 means "not for this URL", a 501 means "not by this server, ever". The most common real-world sighting is a proxy or CDN receiving a method it does not know how to forward, or a server being asked for an extension like WebDAV that is not installed.

## Common causes

- An HTTP method the server does not recognise, such as PATCH on a very old server
- A proxy asked to handle a method it cannot forward
- WebDAV or another extension requested but not installed
- A CGI or FastCGI handler missing for a file type
- A gateway that does not implement a required feature of the request

## If you're just trying to view the page

1. Reload — occasionally a misrouted request produces this
2. Nothing else; the server genuinely lacks a capability and only its operator can add it
3. Report it to the site owner if it happens on a normal page

## If it's your site

1. Check whether the method is genuinely unsupported or just unrouted; if the URL exists but the method does not apply, 405 is the correct code
2. Verify the required module is installed and enabled — mod_dav for WebDAV, the right FastCGI handler for your runtime
3. Check what your CDN or reverse proxy forwards; some block uncommon methods by default

## Reference

- **Status code:** 501
- **Reason phrase:** Not Implemented
- **Category:** 5xx — Server Error
- **Cacheable by default:** Yes
- **Defined in:** RFC 9110 §15.6.2

## Common questions

### What does HTTP 501 mean?

The server does not support the functionality needed to fulfil the request, usually the HTTP method itself. The server does not recognise the request method at all, or cannot support it for any resource. This is broader than 405: a 405 means "not for this URL", a 501 means "not by this server, ever".

### How do I fix a 501 error?

Reload — occasionally a misrouted request produces this

### Is 501 a client error or a server error?

501 is in the 5xx range, which means server error. The request was acceptable but the server could not fulfil it, so retrying later can succeed.

## Related pages

- [500 Internal Server Error](https://atoneplace.net/error/500/)
- [502 Bad Gateway](https://atoneplace.net/error/502/)
- [503 Service Unavailable](https://atoneplace.net/error/503/)
- [504 Gateway Timeout](https://atoneplace.net/error/504/)
- [524 A Timeout Occurred](https://atoneplace.net/error/524/)
- [521 Web Server Is Down](https://atoneplace.net/error/521/)
- [522 Connection Timed Out](https://atoneplace.net/error/522/)
- [520 Web Server Returned an Unknown Error](https://atoneplace.net/error/520/)
- [525 SSL Handshake Failed](https://atoneplace.net/error/525/)
- [526 Invalid SSL Certificate](https://atoneplace.net/error/526/)
- [530 Origin DNS Error](https://atoneplace.net/error/530/)
- [511 Network Authentication Required](https://atoneplace.net/error/511/)

## Sources

- Hypertext Transfer Protocol (HTTP) Status Code Registry — IANA (https://www.iana.org/assignments/http-status-codes/)
- RFC 9110: HTTP Semantics — IETF (https://www.rfc-editor.org/rfc/rfc9110.html)