HTTP 510 — Not Extended
HTTP 510
Not Extended
An obsolete code from an abandoned extension framework; the server wanted extra information the request did not carry.
What 510 actually means
Defined by RFC 2774, an experimental HTTP extension framework that was moved to Historic status and never saw real adoption. IANA now marks the code as obsoleted. The original idea was that a server could declare "your request needs to declare which extensions it uses", and answer 510 when it did not. Nothing meaningful uses it today, and encountering one means something unusual is going on.
Common causes
- A server implementing the abandoned RFC 2774 extension framework
- A bespoke API borrowing the code to mean "missing required extension"
If you're just trying to view the page
- Nothing — this is an obsolete code and effectively never appears in normal use
- Report the URL to the site owner if you genuinely encountered it
If it's your site
- Do not use 510; it is obsoleted and no client implements sensible behaviour for it
- Use 400 or 428 with a clear body if you need to demand something extra from the client
Reference
- Status code
- 510
- Reason phrase
- Not Extended
- Category
- 5xx — Server Error
- Cacheable by default
- No
- Defined in
- RFC 2774 §7 (obsoleted)
Common questions
- What does HTTP 510 mean?
- An obsolete code from an abandoned extension framework; the server wanted extra information the request did not carry. Defined by RFC 2774, an experimental HTTP extension framework that was moved to Historic status and never saw real adoption. IANA now marks the code as obsoleted.
- How do I fix a 510 error?
- Nothing — this is an obsolete code and effectively never appears in normal use
- Is 510 a client error or a server error?
- 510 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
- 501 Not Implemented The server does not support the functionality needed to fulfil the request, usua