HTMLMinifier

HTMLMinifier is a highly configurable, well-tested, JavaScript-based HTML minifier.

See corresponding blog post for all the gory details of how it works, description of each option, testing results and conclusions.

Test suite is available online.

Also see corresponding Ruby wrapper, and for Node.js, Grunt plugin, Gulp module, Koa middleware wrapper and Express middleware wrapper.

For lint-like capabilities take a look at HTMLLint.

Minification comparison

How does HTMLMinifier compare to other solutions — HTML Minifier from Will Peavy (1st result in Google search for "html minifier") as well as htmlcompressor.com and minimize?

Site	Original size (KB)	HTMLMinifier	minimize	Will Peavy	htmlcompressor.com
Google	44	43	45	46	45
CNN	108	97	104	105	102
HTMLMinifier	118	81	101	105	101
New York Times	175	118	127	131	124
BBC	199	161	192	197	188
Stack Overflow	238	184	193	201	191
Bootstrap CSS	276	264	273	231	274
Amazon	372	324	354	366	n/a
Wikipedia	480	437	463	479	n/a
NBC	513	491	511	513	n/a
Eloquent Javascript	870	815	840	864	n/a
ES6 table	3900	3285	3679	3855	n/a
ES6 draft	4796	4247	4376	4499	n/a

Options Quick Reference

Option	Description	Default
caseSensitive	Treat attributes in case sensitive manner (useful for custom HTML tags)	false
collapseBooleanAttributes	Omit attribute values from boolean attributes	false
collapseInlineTagWhitespace	Don't leave any spaces between display:inline; elements when collapsing. Must be used in conjunction with collapseWhitespace=true	false
collapseWhitespace	Collapse white space that contributes to text nodes in a document tree	false
conservativeCollapse	Always collapse to 1 space (never remove it entirely). Must be used in conjunction with collapseWhitespace=true	false
customAttrAssign	Arrays of regex'es that allow to support custom attribute assign expressions (e.g. '<div flex?="{{mode != cover}}"></div>')	[ ]
customAttrCollapse	Regex that specifies custom attribute to strip newlines from (e.g. /ng-class/)
customAttrSurround	Arrays of regex'es that allow to support custom attribute surround expressions (e.g. <input {{#if value}}checked="checked"{{/if}}>)	[ ]
customEventAttributes	Arrays of regex'es that allow to support custom event attributes for minifyJS (e.g. ng-click)	[ /^on[a-z]{3,}$/ ]
decodeEntities	Use direct Unicode characters whenever possible	false
html5	Parse input according to HTML5 specifications	true
ignoreCustomComments	Array of regex'es that allow to ignore certain comments, when matched	[ /^!/ ]
ignoreCustomFragments	Array of regex'es that allow to ignore certain fragments, when matched (e.g. <?php ... ?>, {{ ... }}, etc.)	[ /<%[\s\S]*?%>/, /<\?[\s\S]*?\?>/ ]
includeAutoGeneratedTags	Insert tags generated by HTML parser	true
keepClosingSlash	Keep the trailing slash on singleton elements	false
maxLineLength	Specify a maximum line length. Compressed output will be split by newlines at valid HTML split-points
minifyCSS	Minify CSS in style elements and style attributes (uses clean-css)	false (could be true, Object, Function(text))
minifyJS	Minify JavaScript in script elements and event attributes (uses UglifyJS)	false (could be true, Object, Function(text, inline))
minifyURLs	Minify URLs in various attributes (uses relateurl)	false (could be String, Object, Function(text))
preserveLineBreaks	Always collapse to 1 line break (never remove it entirely) when whitespace between tags include a line break. Must be used in conjunction with collapseWhitespace=true	false
preventAttributesEscaping	Prevents the escaping of the values of attributes	false
processConditionalComments	Process contents of conditional comments through minifier	false
processScripts	Array of strings corresponding to types of script elements to process through minifier (e.g. text/ng-template, text/x-handlebars-template, etc.)	[ ]
quoteCharacter	Type of quote to use for attribute values (' or ")
removeAttributeQuotes	Remove quotes around attributes when possible	false
removeComments	Strip HTML comments	false
removeEmptyAttributes	Remove all attributes with whitespace-only values	false
removeEmptyElements	Remove all elements with empty contents	false
removeOptionalTags	Remove optional tags	false
removeRedundantAttributes	Remove attributes when value matches default.	false
removeScriptTypeAttributes	Remove type="text/javascript" from script tags. Other type attribute values are left intact	false
removeStyleLinkTypeAttributes	Remove type="text/css" from style and link tags. Other type attribute values are left intact	false
removeTagWhitespace	Remove space between attributes whenever possible. Note that this will result in invalid HTML!	false
sortAttributes	Sort attributes by frequency	false
sortClassName	Sort style classes by frequency	false
useShortDoctype	Replaces the doctype with the short (HTML5) doctype	false

Sorting attributes / style classes

Minifier options like sortAttributes and sortClassName won't impact the plain-text size of the output. However, they form long repetitive chains of characters that should improve compression ratio of gzip used in HTTP compression.

Special cases

Ignoring chunks of markup

If you have chunks of markup you would like preserved, you can wrap them <!-- htmlmin:ignore -->.

Preserving SVG tags

SVG tags are automatically recognized, and when they are minified, both case-sensitivity and closing-slashes are preserved, regardless of the minification settings used for the rest of the file.

Working with invalid markup

HTMLMinifier can't work with invalid or partial chunks of markup. This is because it parses markup into a tree structure, then modifies it (removing anything that was specified for removal, ignoring anything that was specified to be ignored, etc.), then it creates a markup out of that tree and returns it.

Input markup (e.g. <p id="">foo)

↓

Internal representation of markup in a form of tree (e.g. { tag: "p", attr: "id", children: ["foo"] })

↓

Transformation of internal representation (e.g. removal of id attribute)

↓

Output of resulting markup (e.g. <p>foo</p>)

HTMLMinifier can't know that original markup was only half of the tree; it does its best to try to parse it as a full tree and it loses information about tree being malformed or partial in the beginning. As a result, it can't create a partial/malformed tree at the time of the output.

Installation Instructions

From NPM for use as a command line app:

npm install html-minifier -g

From NPM for programmatic use:

npm install html-minifier

From Git:

git clone git://github.com/kangax/html-minifier.git
cd html-minifier
npm link .

Usage

For command line usage please see html-minifier --help

Node.js

var minify = require('html-minifier').minify;
var result = minify('<p title="blah" id="moo">foo</p>', {
  removeAttributeQuotes: true
});
result; // '<p title=blah id=moo>foo</p>'

Running benchmarks

Benchmarks for minified HTML:

node benchmark.js