All HTTP status codes
2xx Success
RFC 9110
203 Non-Authoritative Information
The response is from a transforming proxy, not the origin server.
What it means
HTTP 203 indicates that the returned metadata is not exactly the same as is available from the origin server, but is collected from a local or third-party copy. Mostly used by intermediaries that modify responses.
When it's used
Transforming proxies that rewrite headers, content compressors, or CDNs that apply transformations.
Common causes
- Reverse proxy modified the response
- CDN applied compression or transformation
- Caching layer returned a slightly stale variant
How to fix it
- Rare in modern stacks — verify which proxy in your chain is generating it
- If unintended, check Varnish, Squid, or Apache mod_proxy configuration
- Generally safe to treat as 200 in clients
Example response
HTTP/1.1 203 Non-Authoritative Information Content-Type: text/html
SEO impact
Treated as 200 by Google. No negative SEO impact.