HTTP 203 – Non-Authoritative Information
The returned metadata is not exactly the same as from the origin server, but from a local or third-party copy.
Common use case
Used by transforming proxies that modify response headers or bodies in transit, e.g. an ad-stripping proxy or a caching layer that adjusts metadata.
Example
HTTP/1.1 203 Non-Authoritative Information
Content-Type: text/html
<html>...</html>History
Introduced in HTTP/1.1 (RFC 2068, 1997) to distinguish proxy-modified responses from the origin's own 200 OK.
Did you know?
It is one of the least-used status codes on the modern web - most proxies simply forward the origin's 200 unchanged.