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CriticalCSS Bookmarklet and Devtool Snippet.js
(function() {
var CSSCriticalPath = function(w, d, opts) {
var opt = opts || {};
var css = {};
var pushCSS = function(r) {
if(!!css[r.selectorText] === false) css[r.selectorText] = {};
var styles =;(?![A-Za-z0-9])/);
for(var i = 0; i < styles.length; i++) {
if(!!styles[i] === false) continue;
var pair = styles[i].split(": ");
pair[0] = pair[0].trim();
pair[1] = pair[1].trim();
css[r.selectorText][pair[0]] = pair[1];
var parseTree = function() {
// Get a list of all the elements in the view.
var height = w.innerHeight;
var walker = d.createTreeWalker(d, NodeFilter.SHOW_ELEMENT, function(node) { return NodeFilter.FILTER_ACCEPT; }, true);
while(walker.nextNode()) {
var node = walker.currentNode;
var rect = node.getBoundingClientRect();
if( < height || opt.scanFullPage) {
var rules = w.getMatchedCSSRules(node);
if(!!rules) {
for(var r = 0; r < rules.length; r++) {
this.generateCSS = function() {
var finalCSS = "";
for(var k in css) {
finalCSS += k + " { ";
for(var j in css[k]) {
finalCSS += j + ": " + css[k][j] + "; ";
finalCSS += "}\n";
return finalCSS;
var cp = new CSSCriticalPath(window, document);
var css = cp.generateCSS();

PaulKinlan commented Aug 22, 2013

Just added merging of styles.


PaulKinlan commented Aug 22, 2013

Fixing merge of styles.

Hey @PaulKinlan

Not sure if there is a reason why you have chosen to use d.body but I found that using the body as the start node missed body and html styles which could be very important on the critical css. Mind you my understanding of walkers is limited.

var walker = d.createTreeWalker(d, NodeFilter.SHOW_ELEMENT, function(node) { return NodeFilter.FILTER_ACCEPT; }, true);

instead of

var walker = d.createTreeWalker(d.body, NodeFilter.SHOW_ELEMENT, function(node) { return NodeFilter.FILTER_ACCEPT; }, true);


PaulKinlan commented Aug 22, 2013

@GlynnPhillips funny, I had this on my list :) great spot. not sure about head elements but let's give it ago.


PaulKinlan commented Aug 22, 2013

Fixed, head makes thinks look great. noticed a couple of other issues, working on them too.

Awesome, looking better now :)


PaulKinlan commented Aug 23, 2013

@GlynnPhillips I just relaised that it doesn't pull in scripts that are external to your domain (i.e cross-origin), whilst a little inconvienient I think this makes sense.

I see cross-browser issues...

@PaulKinlan in what way? I can see script tags from external domains being 'walked' through. Is it just that it wouldn't pick up any styles which are set by these?

Looks great when I tested on some websites, but it failed miserably on AND, it just returned bunch of selectors with css of { display: none !important; orphans: 4321 !important; }

So what is the issue here??

marcis commented Sep 17, 2013

What about this error message: "Uncaught SyntaxError: Unexpected end of input"?

I'm using Chrome :)

cforge79 commented Oct 4, 2013

great work! just got pagespeed insights of 99 / 100 after moving the styles output to inline css! wow


PaulKinlan commented Oct 22, 2013

@cforge79 - awesome!!

Are there any workarounds for the cross origin thing? I serve all my static content from a different domain to prevent users from sending cookies to it.

Patrick from feed the bot told me about this this is a fantastic set of code you have there. Thank you so much

sigginet commented Nov 7, 2013

@marcis you have to convert it to a bookmarklet (URLencoded, etc) code .. try

@PaulKinlan Is it possible to pick up styles with media queries?

Sorry, possibly unrelated. But I want to test this.
How to use it as bookmark? I even minified it to put in bookmark in chrome but it is not taking. Possibly size!

@satya61229 it should work fine minified... but don't forget you'll need to prefix it with "javascript:" ;-) (oh, and make sure you delete the comments... or the // will terminate your bookmarklet code early)

Hey @PaulKinlan

It should also return the pseudo-elements like ::after, ::before, hover, focus and active as well, check

A little bit of a resurrection, but I couldn't find anything on this problem:

Do you have any solution for the same-origin problem?

It seems that if you deliver your static resources via a CDN, this code will not work, because of the above problem.. I guess we can always temporarily move that CSS to be inline or so for testing, but I was hoping for something without many manual steps. :)

Awesome little tool by the way!

I built my own CriticalCSS Generator to solve these issues, something I can use for production. You can check it out here if you're interested:

Thanks for the inspiration!

Hey @PaulKinlan @pocketjoso

Is there any solution available for CDN served css files ?

I put this script inside a CLI tool (Node) running on top of PhantomJS.

It's good for some automations.

Thanks for de original idea @PaulKinlan

amityweb commented May 7, 2015

Doesn't work for me in Chrome. I made it into a Bookmarklet using

Edit: Ok this gives it away console.log(css); - i can see it now :)

amityweb commented May 7, 2015

Doesn't grab ALL the critical CSS for us... leaves out our header menu, so we get a flash of unstyled content, mainly the header menu

Just found this gem, works really well :)

When executing, I get this warning however:

'getMatchedCSSRules()' is deprecated. For more help, check

@amityweb I suspect it has it has something to do with the positioning of the elements, as it works fine for me on my current project (with a fixed header nav)

Not working for me :( . After fill in only the 'critical path css', your tool gives me, the page is showing up wrong

ctorx commented Aug 20, 2015

It seems the getMatchCSSRules function is expecting 2 arguments. Calling it with an empty string kills the deprecated message and still works as expected.

var rules = w.getMatchedCSSRules(node, '');

It doesn't work for media query and responsive websites. I tried with Bootstrap ( Is there any way to make it work with Bootstrap?

@vuquangchien, this might be of use (I based it off Paul's code when we also hit the media queries issue)

@james-Ballyhoo I tested it, It didn't work well on default brower on Android. It works well on chrome 👍 Can you fix it for all browers?

verkaro commented Sep 9, 2016

non-techie reporting: this doesn't work with chromium-browser in Ubuntu 16.10 -- but running under google's chrome download worked. thanks for the work you've done.

MiFreSu commented Jun 2, 2017

The function getMatchedCSSRules does not work anymore. Long time it was deprecated and now it is removed. Does someone knows a replacement?


Someone wrote a plugin as per your code:
Generate Critical CSS at

but that plugin is out to update, would like to update it?

As per suggestion from google page speed insight, we need generate critical css, some plugins ( only handle optimize, but not handle generate those css.

Anyone would like to update those wordpress' plugin?


optimalisatie commented Jan 24, 2018


Thanks a lot for this snippet!

getMatchedCSSRules will be removed in Chrome 63.

We have created an improved snippet based on this concept that includes a polyfill for getMatchedCSSRules to support more browsers, including Firefox.

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