203 Non-Authoritative Information means the request succeeded, but the content was modified by a transforming proxy compared to the origin server's 200 OK response. It lets the proxy tell the recipient that what it receives is not the original, which may matter for later decisions about the content.
Real-world use is rare. Proxies that recompress images, inject content or filter pages almost always keep the status 200 instead. A 203 is heuristically cacheable, just like a 200.
Example response
HTTP/1.1 203 Non-Authoritative Information
Date: Fri, 06 Nov 2026 10:15:32 GMT
Via: 1.1 filter.example.net
Content-Type: text/html; charset=utf-8
Content-Length: 75
<!doctype html>
<title>News</title>
<p>[content rewritten by the proxy]</p>SEO and redirect checking
Crawlers treat a 203 as a success, like a 200. If you see a 203, some intermediary between the client and the origin, such as a filtering proxy, a mobile carrier's optimiser or a gateway in front of the site, rewrote the content, and other visitors may receive something different.
Common causes and use cases
- A mobile carrier or optimisation proxy recompressed images or minified HTML.
- A content filter or security gateway removed or rewrote parts of the page.
- An API gateway returns data copied from another source and marks it as non-authoritative.