HTTP Status Codes
HTTP 203 Non-Authoritative Information
Non-Authoritative Information — the response was modified by an intermediate proxy
What 203 Means
The 203 error on the HTTP Status Codes indicates non-authoritative information — the response was modified by an intermediate proxy. This typically occurs due to a transforming proxy rewrote headers or content from the origin server.
Status 203 signals that the request was successful, but the returned metadata or body may differ from what the origin server originally sent. A proxy or intermediary altered the response before the client received it.
Technical Background
The 203 Non-Authoritative Information status indicates that the request was successful, but the enclosed payload has been modified by a transforming proxy from the origin server's original 200 response.
This code is rarely seen in practice because most proxies do not signal their modifications. When it does appear, it serves as an honesty mechanism: the proxy is transparently disclosing that the response is not exactly what the origin sent.
Common Causes
- A transforming proxy rewrote headers or content from the origin server
- A CDN or caching layer modified the payload before delivery
- A corporate gateway stripped or replaced parts of the response
Typical Scenarios
- A corporate network proxy injects a disclaimer header into every outbound response
- A caching appliance serves a compressed version of the original page with modified headers
What to Know
A 203 response is functionally successful. The distinction from 200 is primarily informational, alerting the client that an intermediary has altered the payload in transit.
Frequently Asked Questions
Common questions about HTTP 203 error
The content is generally usable, but it may not be identical to what the origin server originally sent. Applications that need byte-exact fidelity should verify against the origin directly.