Last-Modified

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.

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 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

Report problems with this compatibility data on GitHub
desktopmobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Last-Modified

Legend

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Full support
Full support

See also