HTTP 203 Non-Authoritative Information — Proxy Modified Response

HTTP 203 Non-Authoritative Information indicates the response was modified by a proxy or intermediate server before reaching the client. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: The origin server returned 200 but a proxy modified the response. Common with transforming proxies that compress or modify content. The client should be aware the response may differ from the origin. Rarely seen in practice — most proxies do not change the status code. Defined in RFC 7231 Section 6.3.4. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: Transparent proxy modifying response headers or body. CDN applying content transformation (minification, image optimization). Corporate proxy injecting content into the page. Caching proxy returning a modified version of the resource. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: No fix typically needed — the response was successful. If content appears modified, bypass the proxy to get the original response. Check response headers for Via: or X-Cache: to identify the modifying proxy. Use HTTPS to prevent proxy modification (proxies cannot modify encrypted content). Configure CDN to return 200 instead of 203 if the transformation is expected. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

This article is part of our HTTP Status Codes collection on Error Codes Wiki. We provide comprehensive, up-to-date information to help you find solutions quickly.