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Check whether the server returns 304 Not Modified

harmlessSEO checksdebian, ubuntu
Adjust the values, the command updates live
user@server
curl -s -o /dev/null -w '%{http_code}\n' -H "If-Modified-Since: $(curl -sI https://example.com/ | grep -i '^last-modified:' | cut -d' ' -f2- | tr -d '\r')" https://example.com/

First reads the Last-Modified header and sends it back as If-Modified-Since. If the server responds with 304, it supports conditional requests, so Googlebot and browsers do not have to reload unchanged content. A 200 means either the header is missing or the server does not evaluate it.

Note: Dynamic WordPress pages often send no Last-Modified at all, while static files like CSS or images almost always do. The same principle works for ETags with If-None-Match.

Also searched as

  • test 304 not modified curl
  • check if-modified-since support
  • does the server support conditional requests
  • last-modified header working

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