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
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
Last-Modified: Wed, 21 Oct 2015 07:28:00 GMT
Specifications
| Specification |
|---|
| HTTP Semantics # field.last-modified |
Browser compatibility
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