HTTP 304 Not Modified

What Does HTTP 304 Mean?

HTTP 304 Not Modified indicates that the requested resource has not been modified since the last cached version. The server tells the client to use its cached copy, saving bandwidth and improving performance.

HTTP 304 is central to browser caching. When a browser has a cached version of a resource, it sends a conditional request with If-Modified-Since or If-None-Match headers. If the resource hasn't changed, the server returns 304 without a body, and the browser uses its cache.

Proper cache configuration with ETag and Last-Modified headers enables efficient use of 304 responses, significantly reducing page load times and server bandwidth. This is a key component of web performance optimization.

Common Causes of 304 Not Modified

The requested resource has not changed since the client's cached version. The server checks the If-Modified-Since or If-None-Match headers and determines the cache is still valid.

This is normal browser caching behavior, not an error. It saves bandwidth by avoiding retransmission of unchanged resources.

How to Fix 304 Not Modified

HTTP 304 is a normal caching response that improves performance. If you're seeing stale content, clear your browser cache or add cache-busting parameters. For developers: configure proper Cache-Control, ETag, and Last-Modified headers.

To force a fresh response, use Ctrl+Shift+R (hard refresh) or add a version query parameter to URLs.

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