HTTP 304 Not Modified

In short: The cached copy is still current, nothing is transferred again.

In more detail: The browser asks with If-None-Match (ETag) or If-Modified-Since. If the file has not changed, the server answers 304 without a body and the browser uses its copy from the cache. This saves data and load time.

In Depth

When it occurs

• Repeated page visit with a valid cache.
• Images, scripts and stylesheets that rarely change.

What you can do

1. If a page looks outdated: clear the cache or hard reload (Ctrl+F5).
2. Operators: send ETag or Last-Modified so revalidation is possible.

See also: HTTP Status Codes Overview, HTTP