Syntax

If-Unmodified-Since: <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

If-Unmodified-Since: Wed, 21 Oct 2015 07:28:00 GMT

Specifications

Browser compatibility

See also

• HTTP Conditional Requests guide
• Last-Modified
• If-Range, Range range request headers
• If-Match, If-Modified-Since, If-None-Match conditional request headers
• 304 Not Modified, 412 Precondition Failed response status codes