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MDN / Last-Modified header

The HTTP Last-Modified contains a date and time when the origin server believes the resource was last modified. It is used as a validator in conditional requests ( or ) to determine if a requested resource is the same as one already stored by the client. It is less accurate than an 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.

  </th>
  <td>Yes</td>
</tr>

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

Browser compatibility

See also