What it means

A 304 Not Modified response tells the client that its cached version of the resource has not changed and can be reused. This saves bandwidth by not retransmitting the file. The browser sends an If-Modified-Since or If-None-Match header, and if the resource is unchanged, the server responds with 304.

Common causes

• The browser had a cached copy and asked the server if it was still current.
• The server confirmed the cached copy is still valid.

How to fix it

• No action needed. This is a normal and beneficial part of HTTP caching.