501 Not Implemented
The server does not support the functionality required to fulfil the request.
What it means
HTTP 501 Not Implemented means the server does not recognize the request method or lacks the capability to fulfil it. It typically indicates an unsupported HTTP method or a feature the server was never built to handle.
When it happens
It happens when a client uses an uncommon or unsupported method, or requests functionality the server software does not provide.
How to fix it
- Use a standard, supported HTTP method (GET, POST, etc.).
- Confirm the server software supports the feature being requested.
- Update or reconfigure the server if a needed capability is missing.
SEO impact
Negative if it affects real pages. It is uncommon for indexable content, but any 501 on a page crawlers request prevents indexing of that URL.
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Related codes
A generic error meaning the server encountered an unexpected condition.
502 Bad GatewayA server acting as a gateway received an invalid response from the upstream server.
503 Service UnavailableThe server is temporarily unable to handle the request, often due to overload or maintenance.
504 Gateway TimeoutA gateway server did not receive a timely response from the upstream server.
505 HTTP Version Not SupportedThe server does not support the HTTP protocol version used in the request.
506 Variant Also NegotiatesA server misconfiguration in content negotiation causes an internal negotiation loop.
Related guides
A plain-English primer on HTTP status codes for SEOs: what the 2xx, 3xx, 4xx, and 5xx families mean, which ones affect rankings, and the codes worth knowing.
How to find and fix broken linksA practical walkthrough for finding broken links on your site, working out why each one breaks, and fixing them so visitors and crawlers stop hitting dead ends.