HTTP 203 Non-Authoritative Information vs 303 See Other
HTTP 203 (Non-Authoritative Information) is a 2xx Success response, while 303 (See Other) is a 3xx Redirection response. 203 indicates that the response payload has been modified by a transforming proxy from the origin server's 200 response. In contrast, 303 means that the server is redirecting to a different resource using GET, typically after a POST operation (Post/Redirect/Get pattern).
Description
The response payload has been modified by a transforming proxy from the origin server's 200 response.
When You See It
When a proxy or CDN modifies the response body (e.g., adds headers, transforms content).
How to Fix
Check if a proxy is modifying the response. Access the origin directly if you need the original content.
Description
The server is redirecting to a different resource using GET, typically after a POST operation (Post/Redirect/Get pattern).
When You See It
After form submissions to prevent resubmission on browser refresh.
How to Fix
Follow the Location header with a GET request. This is intentional — part of the PRG pattern.
Key Differences
203 is a 2xx Success response, while 303 is a 3xx Redirection response.
HTTP 203: The response payload has been modified by a transforming proxy from the origin server's 200 response.
HTTP 303: The server is redirecting to a different resource using GET, typically after a POST operation (Post/Redirect/Get pattern).
You encounter 203 when when a proxy or CDN modifies the response body (e.g., adds headers, transforms content).
You encounter 303 when after form submissions to prevent resubmission on browser refresh.
When to Use Which
For 203 (Non-Authoritative Information): Check if a proxy is modifying the response. Access the origin directly if you need the original content. For 303 (See Other): Follow the Location header with a GET request. This is intentional — part of the PRG pattern.