304 Not Modified

The HTTP 304 Not Modified client redirection response code indicates that there is no need to retransmit the requested resources. This response code is sent when the request is a conditional GET or HEAD request with an If-None-Match or an If-Modified-Since header and the condition evaluates to false. It is an implicit redirection to a cached resource that would have resulted in a 200 OK response if the condition evaluated to true.

The response must not contain a body and must include the headers that would have been sent in an equivalent 200 OK response: Cache-Control, Content-Location, Date, ETag, Expires, and Vary.

Note: Many developer tools' network panels of browsers create extraneous requests leading to 304 responses, so that access to the local cache is visible to developers.

Status

http
304 Not Modified

Examples

The examples below show GET requests made using curl with conditional request headers and the HTTP responses received in return. The first example would return a 200 OK if we know the resource has been updated since the timestamp in the If-Modified-Since header. For illustration, the request uses a future date of 21st November 2050 to check whether if the resource has been updated since this date:

bash
curl -v --header 'If-Modified-Since: Tue, 21 Nov 2050 08:00:00 GMT' \
 https://developer.mozilla.org/en-US/
http
> Request
GET /en-US/ HTTP/2
Host: developer.mozilla.org
User-Agent: curl/8.1.2
Accept: */*
If-Modified-Since: Tue, 21 Nov 2050 08:00:00 GMT

< Response
HTTP/2 304
date: Tue, 21 Nov 2023 08:44:28 GMT
expires: Tue, 21 Nov 2023 08:53:14 GMT
age: 3194
etag: "e27d81b845c3716cdb5d4220d78e2799"

A 304 Not Modified response is also returned in response to a GET request containing an If-None-Match header with the ETag from the response above. Because the etag exists, a matching entity tag fails the condition, and a 304 response is returned:

bash
curl -v --header 'If-None-Match: "e27d81b845c3716cdb5d4220d78e2799"' \
 https://developer.mozilla.org/en-US/
http
> Request
GET /en-US/ HTTP/2
Host: developer.mozilla.org
User-Agent: curl/8.1.2
Accept: */*
If-None-Match: "e27d81b845c3716cdb5d4220d78e2799"

< Response
HTTP/2 304
date: Tue, 21 Nov 2023 08:47:37 GMT
expires: Tue, 21 Nov 2023 09:38:23 GMT
age: 2920
etag: "e27d81b845c3716cdb5d4220d78e2799"

Specifications

Specification
HTTP Semantics
# status.304

Browser compatibility

BCD tables only load in the browser

Compatibility notes

  • Browser behavior differs if this response erroneously includes a body on persistent connections. See 204 No Content for more detail.

See also