510Not Extended
The server needs the request to include an extension it did not carry.
Browse all HTTP status codesWhen you see it
Part of an extension framework that saw almost no adoption. It is one of the least used codes in the registry and its specification has since been reclassified as obsolete.
If you meet one in the wild it is almost certainly not being used as intended. Some servers borrow unusual codes for their own purposes, so the response body will tell you more than the number does.
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Status codes
69 of 69 codes. Click a row to copy it.
1xx Informational (4)
2xx Success (10)
3xx Redirection (8)
4xx Client errors (31)
5xx Server errors (16)