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Count the number of rules and selectors for CSS files on the page. Flags up the >4096 threshold that confuses IE
function countCSSRules() {
var results = '',
log = '';
if (!document.styleSheets) {
for (var i = 0; i < document.styleSheets.length; i++) {
function countSheet(sheet) {
var count = 0;
if (sheet && sheet.cssRules) {
for (var j = 0, l = sheet.cssRules.length; j < l; j++) {
if( !sheet.cssRules[j].selectorText ) {
count += sheet.cssRules[j].selectorText.split(',').length;
log += '\nFile: ' + (sheet.href ? sheet.href : 'inline <style> tag');
log += '\nRules: ' + sheet.cssRules.length;
log += '\nSelectors: ' + count;
log += '\n--------------------------';
if (count >= 4096) {
results += '\n********************************\nWARNING:\n There are ' + count + ' CSS rules in the stylesheet ' + sheet.href + ' - IE will ignore the last ' + (count - 4096) + ' rules!\n';

I'm getting TypeError: Cannot call method 'split' of undefined

slav commented Nov 12, 2012

so just add if( !sheet.cssRules[j].selectorText ) continue; to the for loop


psebborn commented Jul 12, 2013

@slav - Nice idea, thanks - I've updated the gist now to include that :)

This is awesome, thanks

This won't work if your stylesheets are hosted on another domain due to cross domain permissions voodoo. Just leaving this as a note to anyone using a CDN or something who is confused, as I was, about why it wasn't working.

Awesome, saved me a lot of time, thanks!

Firefox/Firebug errors with:

Error: The operation is insecure.
if (sheet && sheet.cssRules) {

very awesome. i just paste the whole thing in the console window in firebug and it prints it all out

You can avoid the "operation is insecure* error by adding the following code before "if (sheet && sheet.cssRules)

if (sheet.href != null && sheet.href.indexOf(location.origin) != 0){
     console.log("CSS file couldn't be analyzed because it is not on the same domain: " + sheet.href);

AaronV commented Jun 12, 2014

If you add an if statement to count the number of sheets, you can have this also catch IEs bug where it won't load more than 30 stylesheets at a time:

if (document.styleSheets.length >= 30) {
    results += 'Found ' + document.styleSheets.length + ' stylesheets. <= IE9 will ignore stylesheets after 30!\n';

stuff commented Jul 25, 2014

just a word to say it's not so reliable. Got the bug and the script indicate <3800 rules :(

IMHO u should change the print line at the end (count is for selectors, not for rules).

if (count >= 4096) {
results += '\n********************************\nWARNING:\n There are ' + count + ' CSS selectors in the stylesheet ' + sheet.href + ' - IE will ignore the last ' + (count - 4096) + ' selectors!\n';

Same problem here... I got less then 3500 and it still isn't working.

labue commented Aug 26, 2014

Cool snippet, however it does not seem to count the CSSMediaRule objects, only the first level CSSStyleRule. CSSMediaRule can have multiple CSSStyleRule objects within.

I added this:

for (var j = 0, l = sheet.cssRules.length; j < l; j++) {
    if (!sheet.cssRules[j].selectorText) {
        if (sheet.cssRules[j].cssRules) {
            for (var m = 0, n = sheet.cssRules[j].cssRules.length; m < n; m++) {
                count += sheet.cssRules[j].cssRules[m].selectorText.split(',').length;
    else {
        count += sheet.cssRules[j].selectorText.split(',').length;

And went from Rules: 2350, Selectors: 2654 to Rules: 2350, Selectors: 4318.

Thanks @labue! I forked the snippet with your changes

For anyone looking for a Grunt script: (see maxSelectors)

Here's a version that takes @include statements into account:

Just a side-note for people saying it's not reliable because their stylesheet has less than 4096 rules and still breaks in IE9 : the number of selectors isn't the only limit regarding CSS files in IE9-.

  • Number of @import's (31)
  • Nesting @import's (4 levels)
  • File size (278Kb|288Kb)

So yes you may have less than 4096 selectors and still have your stylesheet break in IE9, check for datauri images, auto-generated selectors (compass sprites and @extend for example) and if possible move styles used after load in another stylesheet loaded before the closing body tag (modal popups, jQueryUI stylings, that sort of things) so the broser renders elements that are there right away and loads the rest before it happens on the page if it comes from user interaction.

Thanks for the gist, helped me figure out my problem wasn't a selector limit issue, but removing some datauri images did the trick for me.

in my ie8, the rule 4096 does not apply.
as said justinmarsan "stylesheet has less than 4096 rules"

Using @krisbulman's function gave me the actual results i was looking for.

wesbot commented Jun 12, 2015

Brilliant job, thanks!

Saw this and just had to remake it with es6.

This snippet counts selectors recursively, so it also finds selectors inside media-queries. Also it requires a modern browser.

  var countSelectorsInStylesheet = container => Array.from(container.cssRules).reduce((prev, cur) => {
    prev = rule.selectorText ? prev + rule.selectorText.split(',').length : prev;
    prev = rule.cssRules ? prev + countSelectorsInStylesheet(rule) : prev; 
  Array.from(document.styleSheets).forEach(sheet => console.log(sheet.href, countRules(sheet), 'selectors'));

have fun!

This is great! Saved me a ton of time. As colinbashbash said, I opened Firebug, pasted the code into the console window and clicked run. It took me 30 seconds at the most.

ka2n commented Dec 20, 2016

A modified version of @screeny05's snippet, works well on Google Chrome's console.

  var countSelectorsInStylesheet = container => Array.from(container.cssRules).reduce((prev, rule) => {
    prev = rule.selectorText ? prev + rule.selectorText.split(',').length : prev;
    prev = rule.cssRules ? prev + countSelectorsInStylesheet(rule) : prev
    return prev
  }, 0);
  Array.from(document.styleSheets).forEach(sheet => console.log(sheet.href ? sheet.href : "inline", countSelectorsInStylesheet(sheet), 'selectors'));

This thread is nice and helpful! I got errors on @ka2n and @screeny05 on Chrome 59. @welsh-dwarf works out-of-the-box!

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