203 Non-Authoritative Information HTTP Status Code

Description

HTTP status code 203 indicates a "Non-Authoritative Information" response. This status code is a part of the HTTP/1.1 standard. It means that the request was successful, and the server is returning meta-information that is not from the origin server, but from a third party. Essentially, while the request itself was successful and the server has successfully processed the request, the information that is being returned is from a secondary source rather than the original or authoritative source.

This can happen in situations where a proxy or intermediary server is in place between the client (the requester) and the origin server. The proxy may modify the original response from the server or provide its own information in place of the server's response. For instance, a caching proxy might return a response based on its cached data rather than the actual data from the origin server, if it deems the cached data to be sufficiently up-to-date.

While receiving a 203 response is generally a sign that the request was processed successfully, it also serves as a hint to the client that the returned data might not be exactly what the origin server would have provided, urging the client to treat this information with a slight caution or to validate it if necessary.

Status

HTTP

203 Non-Authoritative Information

Common Causes

Here are the primary causes or scenarios where a 203 status code might be used:

Proxy Servers or Intermediaries: When a user's request goes through a proxy server or any intermediary server, the response might be modified or enriched with additional headers. If the proxy server adds or modifies information in the entity-header of the response that it forwards to the client, but the response's payload is still considered to be what was provided by the origin server, a 203 status code might be returned.
Caching Servers: Similar to proxy servers, caching servers store copies of web documents accessed through them. A caching server might return a 203 status code when it serves a cached response that includes metadata not exactly the same as the origin server would have provided, possibly because the cache added, modified, or omitted some headers for its purposes (e.g., to manage the cache).
Content Modification by ISPs: In some cases, Internet Service Providers (ISPs) might inject ads, notifications, or other content into web pages as they are delivered to users. If such modifications are made to the response content or metadata and the ISP wishes to indicate that the response has been altered from the original, a 203 status code could theoretically be used, although this practice is controversial and generally discouraged.
Transformation Services: Services that modify or transform content for specific purposes, such as to optimize images for faster loading, to provide translations, or to adapt content for mobile devices, might use a 203 status code to indicate that the content has been successfully processed and delivered, but with modifications from the original.

It's important to note that the use of 203 status code is not very common, and its specific use cases might vary depending on the architecture and design of the web service and its intermediary components. Generally, it serves as a signal to the client that the response payload is essentially what was expected, but the metadata associated with it might have been altered from what the origin server would provide.