Last-Modified
The Last-Modified
response HTTP header contains a date
and time when the origin server believes the resource was last modified. It is used
as a validator to determine if the resource is the same as the previously stored one. Less accurate
than an ETag
header, it is a fallback mechanism. Conditional requests
containing If-Modified-Since
or If-Unmodified-Since
headers make use of this field.
Last-Modified
is also used by crawlers to adjust crawl frequency, by browsers in heuristic caching, and by content management systems (CMS) to display the time the content was last modified.
Header type | Representation header |
---|---|
Forbidden header name | no |
CORS-safelisted response header | yes |
Syntax
http
Last-Modified: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMT
Directives
- <day-name>
-
One of "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", or "Sun" (case-sensitive).
- <day>
-
2 digit day number, e.g. "04" or "23".
- <month>
-
One of "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" (case sensitive).
- <year>
-
4 digit year number, e.g. "1990" or "2016".
- <hour>
-
2 digit hour number, e.g. "09" or "23".
- <minute>
-
2 digit minute number, e.g. "04" or "59".
- <second>
-
2 digit second number, e.g. "04" or "59".
GMT
-
Greenwich Mean Time. HTTP dates are always expressed in GMT, never in local time.
Examples
http
Last-Modified: Wed, 21 Oct 2015 07:28:00 GMT
Specifications
Specification |
---|
HTTP Semantics # field.last-modified |
Browser compatibility
BCD tables only load in the browser