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    0.12.10 • Public • Published


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    CSS selectors complexity and performance analyzer. analyze-css is built as a set of rules bound to events fired by CSS parser. Each rule can generate metrics and add "offenders" with more detailed information (see Usage section for an example).


    analyze-css comes as a "binary" for command-line and as CommonJS module. Run the following to install them globally:

    npm install --global analyze-css


    Command line tool

    You can use analyze-css "binary" to analyze local CSS files or remote CSS assets:

    analyze-css --file examples/elecena.css
    analyze-css --url
    analyze-css --url --ignore-ssl-errors

    You can provide CSS via stdin as well (notice the dash: -):

    echo ".foo {margin: 0 \!important}" | analyze-css -

    This will emit JSON formatted results on stdout. Use --pretty (or -p shortcut) option to make the output readable for human beings.

    Basic HTTP authentication can be provided through the options --auth-user and --auth-pass.

    HTTP proxy (e.g. http://localhost:8080) can be provided via:

    • --proxy or -x option
    • HTTP_PROXY env variable

    CommonJS module

    var analyzer = require('analyze-css');
    new analyzer('.foo {margin: 0 !important}', function(err, results) {
      console.log(results); // example? see below
    // options can be provided
    var opts = {
      'noOffenders': true
    new analyzer('.foo {margin: 0 !important}', opts, function(err, results) {
      console.log(results); // example? see below

    grunt task

    Created by @DeuxHuitHuit

    npm i grunt-contrib-analyze-css

    It uses configurable threshold and compares the analyze-css result with it.


      "generator": "analyze-css v0.10.2",
      "metrics": {
        "base64Length": 11332,
        "redundantBodySelectors": 0,
        "redundantChildNodesSelectors": 1,
        "colors": 106,
        "comments": 1,
        "commentsLength": 68,
        "complexSelectors": 37,
        "duplicatedSelectors": 7,
        "duplicatedProperties": 24,
        "emptyRules": 0,
        "expressions": 0,
        "oldIEFixes": 51,
        "imports": 0,
        "importants": 3,
        "mediaQueries": 0,
        "notMinified": 0,
        "multiClassesSelectors": 74,
        "parsingErrors": 0,
        "oldPropertyPrefixes": 79,
        "propertyResets": 0,
        "qualifiedSelectors": 28,
        "specificityIdAvg": 0.04,
        "specificityIdTotal": 25,
        "specificityClassAvg": 1.27,
        "specificityClassTotal": 904,
        "specificityTagAvg": 0.79,
        "specificityTagTotal": 562,
        "selectors": 712,
        "selectorLengthAvg": 1.5722460658082975,
        "selectorsByAttribute": 92,
        "selectorsByClass": 600,
        "selectorsById": 25,
        "selectorsByPseudo": 167,
        "selectorsByTag": 533,
        "length": 55173,
        "rules": 433,
        "declarations": 1288
      "offenders": {
        "importants": [
          ".foo {margin: 0 !important}"


    • base64Length: total length of base64-encoded data in CSS source (will warn about base64-encoded data bigger than 4 kB)
    • redundantBodySelectors: number of redundant body selectors (e.g. body .foo, section body h2, but not body > h1)
    • redundantChildNodesSelectors: number of redundant child nodes selectors (e.g. ul li, table tr)
    • colors: number of unique colors used in CSS
    • comments: number of comments in CSS source
    • commentsLength: length of comments content in CSS source
    • complexSelectors: number of complex selectors (consisting of more than three expressions, e.g. header ul li .foo)
    • duplicatedSelectors: number of CSS selectors defined more than once in CSS source
    • duplicatedProperties: number of CSS property definitions duplicated within a selector
    • emptyRules: number of rules with no properties (e.g. .foo { })
    • expressions: number of rules with CSS expressions (e.g. expression( document.body.clientWidth > 600 ? "600px" : "auto" ))
    • oldIEFixes: number of fixes for old versions of Internet Explorer (e.g. * html .foo {} and .foo { *zoom: 1 }, read more)
    • imports number of @import rules
    • importants: number of properties with value forced by !important
    • mediaQueries: number of media queries (e.g. @media screen and (min-width: 1370px))
    • notMinified: set to 1 if the provided CSS is not minified
    • multiClassesSelectors: reports selectors with multiple classes (e.g.
    • parsingErrors: number of CSS parsing errors
    • oldPropertyPrefixes: number of properties with no longer needed vendor prefix, powered by data provided by autoprefixer (e.g. --moz-border-radius)
    • propertyResets: number of accidental property resets
    • qualifiedSelectors: number of qualified selectors (e.g. header#nav, .foo#bar, h1.title)
    • specificityIdAvg: average specificity for ID
    • specificityIdTotal: total specificity for ID
    • specificityClassAvg: average specificity for class, pseudo-class or attribute
    • specificityClassTotal: total specificity for class, pseudo-class or attribute
    • specificityTagAvg: average specificity for element
    • specificityTagTotal: total specificity for element
    • selectors: number of selectors (e.g. .foo, .bar { color: red } is counted as two selectors - .foo and .bar)
    • selectorLengthAvg: average length of selector (e.g. for .foo .bar, #test div > span { color: red } will be set as 2.5)
    • selectorsByAttribute: number of selectors by attribute (e.g. .foo[value=bar])
    • selectorsByClass: number of selectors by class
    • selectorsById: number of selectors by ID
    • selectorsByPseudo: number of pseudo-selectors (e,g. :hover)
    • selectorsByTag: number of selectors by tag name
    • length: length of CSS source (in bytes)
    • rules: number of rules (e.g. .foo, .bar { color: red } is counted as one rule)
    • declarations: number of declarations (e.g. .foo, .bar { color: red } is counted as one declaration - color: red)

    Read more

    Dev hints

    Running tests and linting the code:

    npm test && npm run-script lint

    Turning on debug mode (i.e. verbose logging to stderr via debug module):

    DEBUG=analyze-css* analyze-css ...


    npm i analyze-css@0.12.10





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