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
- Reload — occasionally a misrouted request produces this
- Nothing else; the server genuinely lacks a capability and only its operator can add it
- Report it to the site owner if it happens on a normal page
If it's your site
- 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
- Verify the required module is installed and enabled — mod_dav for WebDAV, the right FastCGI handler for your runtime
- 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 Something went wrong on the server and it has no more specific code to describe
- 502 Bad Gateway A proxy or gateway reached the server behind it and got back a broken response,
- 503 Service Unavailable The server is temporarily unable to handle the request, usually because it is ov
- 504 Gateway Timeout A proxy or gateway waited for the server behind it and gave up before an answer
- 524 A Timeout Occurred Cloudflare connected to the origin successfully but the origin did not finish re
- 521 Web Server Is Down Cloudflare could not connect to the origin server because it refused the connect
- 522 Connection Timed Out Cloudflare tried to open a connection to the origin server and never got a reply
- 520 Web Server Returned an Unknown Error Cloudflare reached the origin server but got back a response it could not make s
- 525 SSL Handshake Failed The TLS handshake between Cloudflare and the origin server failed.
- 526 Invalid SSL Certificate The origin server presented a TLS certificate that Cloudflare could not validate
- 530 Origin DNS Error A Cloudflare error shown alongside a 1xxx error code that carries the real expla
- 511 Network Authentication Required You need to log in to the network itself — this is a captive portal, not the sit