What it means
Unlike 405, where the resource exists but the method isn't allowed for it, 501 says the server doesn't support the method at all, for any resource. It's also used for API features that haven't been implemented yet.
Most common causes
- A non-standard or new HTTP method the server doesn't recognise.
- An API feature that has been announced but not built yet.
- An old proxy or device that doesn't support the required feature.
What you can do as a visitor
- You can't fix this as a visitor. Try again later or with a different browser.
What the site owner or developer should do
- For known methods the resource doesn't allow, return 405 with an Allow header.
- For unimplemented features, return 501 with a clear message.
- Check whether an intermediate proxy supports the methods you use.
Impact on SEO and Google
501 is rare; if a server returns it for GET requests on public pages, Google won't index them.
Frequently asked questions
501 or 405?
405: the method isn't allowed for this resource. 501: the server doesn't support the method at all.
Is a 501 a temporary error?
No, it usually stays until a developer adds support.