203 Non-Authoritative Information
The request succeeded, but an intermediary modified the payload it received from the origin server.
Status
HTTP/1.1 203 Non-Authoritative Information
Details
- Category: 2xx
- Status: Standard. Registered with IANA and defined by a current standards-track RFC.
- Specification: RFC 9110 §15.3.4
- Cacheable: Cacheable by default
- Response body: Allowed
- Retry: Not applicable
203 is 200 with a disclosure attached: some hop between the origin and the client changed the response. Typical modifications are image recompression by a mobile carrier, script injection by a filtering proxy, or content adaptation by an enterprise gateway.
The code is rare in the wild because most intermediaries that rewrite payloads simply pass the original 200 through without admitting to it. When you do see it, the body is still usable, but it is no longer byte-identical to what the origin sent.
Headers
- Warning: Historically used to describe the transformation. Deprecated in RFC 9111 but still emitted by older intermediaries.
Common causes
- A transforming proxy compressed images or stripped elements to save bandwidth.
- A corporate gateway rewrote the response to inject a banner or filter content.
How to fix it
As the client
- Do not treat the payload as authoritative for anything security relevant such as signatures or hashes.
- Send Cache-Control: no-transform on requests where modification is unacceptable.
As the server
- Set Cache-Control: no-transform on responses that must reach the client unmodified.
- Serve over HTTPS. Transforming proxies cannot rewrite what they cannot read.
Examples
GET /images/hero.jpg HTTP/1.1 Host: www.example.com HTTP/1.1 203 Non-Authoritative Information Content-Type: image/jpeg Content-Length: 18422 Warning: 214 carrier-proxy "Transformation applied"
Notes for proxy users
Seeing 203 while scraping means something in the path is rewriting bodies, which will corrupt content comparisons and hash checks. A dedicated proxy that forwards traffic without transformation avoids the whole class of problem.