HTTP 304 Not Modified: Meaning and Examples

What HTTP 304 means

When a client revalidates a cached response with If-None-Match (ETag) or If-Modified-Since, the server returns 304 with no body if nothing changed. The client keeps using its cached copy, saving bandwidth. Seeing many 304s in DevTools is a good sign that caching works.

Using 304 correctly

If you always get 200 instead of 304, check that the server sends a stable ETag or Last-Modified. Some load balancers generate different ETags on each server.

Retrying

Not applicable: this isn’t an error.

Example response

HTTP/1.1 304 Not Modified
Date: Wed, 21 Oct 2026 10:30:00 GMT
ETag: "33a64df5"
Cache-Control: max-age=0, must-revalidate

How to return 304

Node.js (Express)

res.status(304).end();

Python (FastAPI)

from fastapi import Response

return Response(status_code=304)

Go (net/http)

w.WriteHeader(http.StatusNotModified)

Related status codes

200 OK : The request succeeded and the response contains the result.
412 Precondition Failed : A condition in the request headers, such as If-Match, was not met.
206 Partial Content : The server is returning only the byte range the client asked for.

Other 3xx status codes

300 Multiple Choices · 301 Moved Permanently · 302 Found · 303 See Other · 307 Temporary Redirect · 308 Permanent Redirect

See the full list of HTTP status codes.

Sources

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Frequently asked questions

What does HTTP 304 Not Modified mean?

HTTP 304 Not Modified tells the client its cached copy is still valid, so no body is sent. When a client revalidates a cached response with If-None-Match (ETag) or If-Modified-Since, the server returns 304 with no body if nothing changed. The client keeps using its cached copy, saving bandwidth. Seeing many 304s in DevTools is a good sign that caching works.