203 Non-authoritative Information

The request was successful but the enclosed payload has been modified from that of the origin server's 200 OK response by a transforming proxy¹.

This status code allows the proxy to notify recipients when a transformation has been applied, since that knowledge might impact later decisions regarding the content. For example, future cache validation requests for the content might only be applicable along the same request path (through the same proxies).

The 203 response is similar to the Warning code of 214 Transformation Applied² which has the advantage of being applicable to responses with any status code.

A 203 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls³.

¹ Transformations RFC7230 Section 5.7.2
² Warning RFC7234 Section 5.5
³ Calculating Heuristic Freshness RFC7234 Section 4.2.2
Source: RFC7231 Section 6.3.4

203 Code references

Go HTTP Status Constant http.StatusNonAuthoritativeInfo
Python3+ HTTP Status Constant http.client.NON_AUTHORITATIVE_INFORMATION
Python3.5+ HTTP Status Constant http.HTTPStatus.NON_AUTHORITATIVE_INFORMATION
Rails HTTP Status Symbol :non_authoritative_information
Symfony HTTP Status Constant Response::HTTP_NON_AUTHORITATIVE_INFORMATION

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