3xx Redirection

HTTP 304 Not Modified

The resource has not been modified since the last request (caching mechanism).

When is 304 used?

Browser cache validation
ETag and If-Modified-Since conditional requests
Reducing bandwidth usage

How to handle a 304 response

Follow the Location header. Most HTTP clients do this automatically, and curl -L follows redirects on the command line. Update links and sitemaps that point at permanently redirected URLs.

Check the status code a URL returns from the command line:

curl -s -o /dev/null -w "%{http_code}\n" https://example.com

How to return 304 from your server

Node.js (Express)

res.sendStatus(304);

Python (Flask)

return "", 304

Go (net/http)

w.WriteHeader(304)

Frequently Asked Questions

What does HTTP 304 mean?

304 Not Modified: The resource has not been modified since the last request (caching mechanism).

Is 304 an error?

No. 304 is in the 3xx Redirection class. Redirection: the client must take additional action, usually requesting a different URL.