Last-Modified header

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

See full compatibility

The HTTP Last-Modified response header contains a date and time when the origin server believes the resource was last modified. It is used as a validator in conditional requests (If-Modified-Since or If-Unmodified-Since) to determine if a requested resource is the same as one already stored by the client. It is less accurate than an ETag for determining file contents, but can be used as a fallback mechanism if ETags are unavailable.

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	Response header, Representation header
Forbidden request header	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

	desktop					mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on iOS	Samsung Internet	WebView Android	WebView on iOS
`Last-Modified`	Chrome – Full support Chrome 1 (Release date: 2008-12-11) footnote Full support	Edge – Full support Edge 12 (Release date: 2015-07-29) footnote Full support	Firefox – Full support Firefox 1 (Release date: 2004-11-09) footnote Full support	Opera – Full support Opera 15 (Release date: 2013-07-02) footnote Full support	Safari – Full support Safari 1 (Release date: 2003-06-23) footnote Full support	Chrome Android – Full support Chrome Android 18 (Release date: 2012-06-27) footnote Full support	Firefox for Android – Full support Firefox for Android 4 (Release date: 2011-03-29) footnote Full support	Opera Android – Full support Opera Android 14 (Release date: 2013-05-21) footnote Full support	Safari on iOS – Full support Safari on iOS 1 (Release date: 2007-06-29) footnote Full support	Samsung Internet – Full support Samsung Internet 1 (Release date: 2013-04-27) footnote Full support	WebView Android – Full support WebView Android 4.4 (Release date: 2013-12-09) footnote Full support	WebView on iOS – Full support WebView on iOS 1 (Release date: 2007-06-29) footnote Full support

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Full support: Full support