The HTTP response status code 203 Non-Authoritative Information is used by proxies to signify that the HTTP request was successful, but the content of the message body has been altered. This suggests that the information within the response may originate from a different source than expected.

The message body's default behavior is cacheable, but if necessary, the response can override this by including appropriate HTTP caching headers.

When receiving the 203 Non-Authoritative Information status code, it indicates the success of the HTTP request, but it does not reveal the original status code. Therefore, the client remains unaware of whether the actual HTTP response status code is 200 OK, 201 Created, or any other code.

The use of the 203 Non-Authoritative Information status code may sometimes be discouraged for this reason. An alternative approach is to send a Warning HTTP header with status code 214 Transformation Applied, which indicates that a transformation has been applied while preserving the original status code.

In this sample, the client initiates a request for a resource, passing through an intermediate proxy server. Although the hosting server stores the resource in plain text format, the proxy server transforms it into JSON format before relaying it back to the client.

Request
GET /instructions HTTP/1.1
Host: www.example.com

Response
HTTP/1.1 200 OK
Content-Type: text/plain; charset=UTF-8
Content-Length: 250

< message body will follow in text format > Response from proxy server to client
HTTP/1.1 203 Non-Authoritative Information
Content-Type: application/json
Content-Length: 265

{“response":"< message body will be embedded in this JSON object >"}

The 203 Non-Authoritative Information HTTP status code indicates that the requested resource has been successfully retrieved, but it may have been modified or transformed by an intermediary before reaching the client.

As a result, the client should exercise caution when relying on the information received, as it may not be entirely authoritative or identical to the original resource.