HTTP 303 See Other vs 428 Precondition Required
HTTP 303 (See Other) is a 3xx Redirection response, while 428 (Precondition Required) is a 4xx Client Error response. 303 indicates that the server is redirecting to a different resource using GET, typically after a POST operation (Post/Redirect/Get pattern). In contrast, 428 means that the server requires the request to be conditional (e.g., include If-Match header) to prevent lost updates.
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.
Description
The server requires the request to be conditional (e.g., include If-Match header) to prevent lost updates.
When You See It
When an API requires optimistic concurrency control via ETags.
How to Fix
Fetch the resource first to get its ETag, then include If-Match in your update request.
Key Differences
303 is a 3xx Redirection response, while 428 is a 4xx Client Error response.
HTTP 303: The server is redirecting to a different resource using GET, typically after a POST operation (Post/Redirect/Get pattern).
HTTP 428: The server requires the request to be conditional (e.g., include If-Match header) to prevent lost updates.
You encounter 303 when after form submissions to prevent resubmission on browser refresh.
You encounter 428 when when an API requires optimistic concurrency control via ETags.
When to Use Which
For 303 (See Other): Follow the Location header with a GET request. This is intentional — part of the PRG pattern. For 428 (Precondition Required): Fetch the resource first to get its ETag, then include If-Match in your update request.