What it means
The request succeeded, but a transforming proxy modified the payload from the origin's 200 response.
Common causes
- A proxy compressed images or rewrote HTML
- A mobile carrier or corporate proxy altered content
How to fix it
As a client or visitor
Treat it like 200, but be aware the content is not exactly what the origin sent. Use HTTPS to prevent intermediaries from changing responses.
As the site or API owner
Origins almost never send 203. If you run a transforming proxy, send Cache-Control: no-transform from the origin to opt out.
Example response
HTTP/1.1
HTTP/1.1 203 Non-Authoritative Information
Date: Tue, 07 Oct 2025 09:30:00 GMT
Server: nginx
Content-Length: 0Specification
FAQ
› Is 203 an error?
No. It is a success code that signals the body was changed by an intermediary.
› How do I stop proxies altering my content?
Serve over HTTPS and add Cache-Control: no-transform.