What requests do browsers’ “F5” and “Ctrl + F5” refreshes generate

browsercachingcross-browserhttprefresh

Is there a standard for what actions F5 and Ctrl+F5 trigger in web browsers?

I once did experiment in IE6 and Firefox 2.x. The F5 refresh would trigger a HTTP request sent to the server with an If-Modified-Since header, while Ctrl+F5 would not have such a header. In my understanding, F5 will try to utilize cached content as much as possible, while Ctrl+F5 is intended to abandon all cached content and just retrieve all content from the servers again.

But today, I noticed that in some of the latest browsers (Chrome, IE8) it doesn't work in this way anymore. Both F5 and Ctrl+F5 send the If-Modified-Since header.

So how is this supposed to work, or (if there is no standard) how do the major browsers differ in how they implement these refresh features?

Best Solution

It is up to the browser but they behave in similar ways.

F5 usually updates the page only if it is modified. Modern browsers sends Cache-Control: max-age=0 to tell any cache the maximum amount of time a resource is considered fresh, relative to the time of the request.

CTRL-F5 is used to force an update, disregarding any cache. Modern browsers sends Cache-Control: no-cache and Pragma: No-cache

If I remember correctly it was Netscape which was the first browser to add support for cache-control by adding Pragma: No-cache when you pressed CTRL-F5.

┌───────────┬──────────────┬─────┬─────────────────┬──────────────────────────────┐
│ Version 4 │      F5      │  R  │      CLICK      │ Legend:                      │
│2021 MAY 19├──┬──┬──┬──┬──┼──┬──┼──┬──┬──┬──┬──┬──┤ C = Cache-Control: no-cache  │
│           │  │S │C │A │A │C │C │  │S │C │A │A │C │ I = If-Modified-Since        │
│           │  │H │T │L │L │T │T │  │H │T │L │L │T │ M = Cache-Control: max-age=0 │
│           │  │I │R │T │T │R │R │  │I │R │T │T │R │ N = Not tested               │
│           │  │F │L │  │G │L │L │  │F │L │  │G │L │ P = Pragma: No-cache         │
│           │  │T │  │  │R │  │+ │  │T │  │  │R │+ │ - = ignored                  │
│           │  │  │  │  │  │  │S │  │  │  │  │  │S │                              │
│           │  │  │  │  │  │  │H │  │  │  │  │  │H │ With 'CLICK' I refer to a    │
│           │  │  │  │  │  │  │I │  │  │  │  │  │I │ mouse click on the browsers  │
│           │  │  │  │  │  │  │F │  │  │  │  │  │F │ refresh-icon.                │
│           │  │  │  │  │  │  │T │  │  │  │  │  │T │                              │
│           │  │  │  │  │  │  │  │  │  │  │  │  │  │ 1: Version 3.0.6 sends I     │
├───────────┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┤    and C, but 3.1.6 opens    │
│Brave 1.24 │M │CP│CP│- │- │M │CP│M │CP│CP│M │CP│CP│    the page in a new tab,    │
├───────────┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┤    making a normal request   │
│Chrome 1   │MI│MI│MI│- │- │MI│- │MI│MI│MI│MI│MI│N │    with only I.              │
│Chrome 6   │MI│CP│CP│- │- │MI│CP│MI│CP│CP│MI│- │N │ 2: Version 10.62 does        │
│Chrome 90  │M │CP│CP│- │- │M │CP│M │CP│CP│M │CP│CP│    nothing. 9.61 might do C  │
├───────────┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┤    unless it was a typo in   │
│Edge 90    │M │CP│CP│- │- │M │CP│M │CP│CP│M │CP│CP│    my old table.             │
├───────────┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┤ 3: Opens the currernt tab in │
│Firefox 3.x│MI│- │CP│- │- │MI│CP│MI│CP│1 │M │MI│N │    a new tab, but does not   │
│Firefox 89 │M │- │CP│- │M │M │CP│M │CP│3 │M │M │3 │    refresh the page if it is │
├───────────┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┤    cached in the browser.    │
│MSIE 8, 7  │I │- │C │- │I │I │  │I │I │C │I │I │N │                              │
├───────────┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┤                              │
│Opera 10, 9│C │- │- │2 │- │C │- │C │C │C │C │- │N │                              │
│Opera 76   │M │CP│CP│- │- │M │- │M │CP│CP│M │CP│CP│                              │
├───────────┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──────────────────────────────┤
│                    https://stackoverflow.com/a/385491/36866                     │
└─────────────────────────────────────────────────────────────────────────────────┘

Note about Chrome 6.0.472: If you do a forced reload (like CTRL-F5) it behaves like the url is internally marked to always do a forced reload. The flag is cleared if you go to the address bar and press enter.