Minify HTML for WordPress without a Plugin - Add to function.php

WP-HTML-Compression

<?php
class WP_HTML_Compression
{
    // Settings
    protected $compress_css = true;
    protected $compress_js = true;
    protected $info_comment = true;
    protected $remove_comments = true;

    // Variables
    protected $html;
    public function __construct($html)
    {
   	 if (!empty($html))
   	 {
   		 $this->parseHTML($html);
   	 }
    }
    public function __toString()
    {
   	 return $this->html;
    }
    protected function bottomComment($raw, $compressed)
    {
   	 $raw = strlen($raw);
   	 $compressed = strlen($compressed);
   	 
   	 $savings = ($raw-$compressed) / $raw * 100;
   	 
   	 $savings = round($savings, 2);
   	 
   	 return '<!--HTML compressed, size saved '.$savings.'%. From '.$raw.' bytes, now '.$compressed.' bytes-->';
    }
    protected function minifyHTML($html)
    {
   	 $pattern = '/<(?<script>script).*?<\/script\s*>|<(?<style>style).*?<\/style\s*>|<!(?<comment>--).*?-->|<(?<tag>[\/\w.:-]*)(?:".*?"|\'.*?\'|[^\'">]+)*>|(?<text>((<[^!\/\w.:-])?[^<]*)+)|/si';
   	 preg_match_all($pattern, $html, $matches, PREG_SET_ORDER);
   	 $overriding = false;
   	 $raw_tag = false;
   	 // Variable reused for output
   	 $html = '';
   	 foreach ($matches as $token)
   	 {
   		 $tag = (isset($token['tag'])) ? strtolower($token['tag']) : null;
   		 
   		 $content = $token[0];
   		 
   		 if (is_null($tag))
   		 {
   			 if ( !empty($token['script']) )
   			 {
   				 $strip = $this->compress_js;
   			 }
   			 else if ( !empty($token['style']) )
   			 {
   				 $strip = $this->compress_css;
   			 }
   			 else if ($content == '<!--wp-html-compression no compression-->')
   			 {
   				 $overriding = !$overriding;
   				 
   				 // Don't print the comment
   				 continue;
   			 }
   			 else if ($this->remove_comments)
   			 {
   				 if (!$overriding && $raw_tag != 'textarea')
   				 {
   					 // Remove any HTML comments, except MSIE conditional comments
   					 $content = preg_replace('/<!--(?!\s*(?:\[if [^\]]+]|<!|>))(?:(?!-->).)*-->/s', '', $content);
   				 }
   			 }
   		 }
   		 else
   		 {
   			 if ($tag == 'pre' || $tag == 'textarea')
   			 {
   				 $raw_tag = $tag;
   			 }
   			 else if ($tag == '/pre' || $tag == '/textarea')
   			 {
   				 $raw_tag = false;
   			 }
   			 else
   			 {
   				 if ($raw_tag || $overriding)
   				 {
   					 $strip = false;
   				 }
   				 else
   				 {
   					 $strip = true;
   					 
   					 // Remove any empty attributes, except:
   					 // action, alt, content, src
   					 $content = preg_replace('/(\s+)(\w++(?<!\baction|\balt|\bcontent|\bsrc)="")/', '$1', $content);
   					 
   					 // Remove any space before the end of self-closing XHTML tags
   					 // JavaScript excluded
   					 $content = str_replace(' />', '/>', $content);
   				 }
   			 }
   		 }
   		 
   		 if ($strip)
   		 {
   			 $content = $this->removeWhiteSpace($content);
   		 }
   		 
   		 $html .= $content;
   	 }
   	 
   	 return $html;
    }
   	 
    public function parseHTML($html)
    {
   	 $this->html = $this->minifyHTML($html);
   	 
   	 if ($this->info_comment)
   	 {
   		 $this->html .= "\n" . $this->bottomComment($html, $this->html);
   	 }
    }
    
    protected function removeWhiteSpace($str)
    {
   	 $str = str_replace("\t", ' ', $str);
   	 $str = str_replace("\n",  '', $str);
   	 $str = str_replace("\r",  '', $str);
   	 
   	 while (stristr($str, '  '))
   	 {
   		 $str = str_replace('  ', ' ', $str);
   	 }
   	 
   	 return $str;
    }
}

function wp_html_compression_finish($html)
{
    return new WP_HTML_Compression($html);
}

function wp_html_compression_start()
{
    ob_start('wp_html_compression_finish');
}
add_action('get_header', 'wp_html_compression_start');
?>

Hey Seth, works like a charm and compresses HTML, but I've noticed it disables Revolution Slider from displaying. Any thoughts?

That's Awesome!
Thank You 🥇

That's works! Thanks.

Working gratefully .. Thanks a lot!

Working great Seth. Thanks!

Life saver!!

It only compresses HTML in <head> element

Works fine but i have problems in some premium templates.
Excellent!

Works for me.

Really help full.

nice effort for make this code, thank's

Thanks. It's a good one but aint working on https( Is any ideas what it cant be?

It was removing the schema added to html is there any possibility to do without affecting schema ?

This is great!

I wrote this script in 2015, five years ago, so I would expect for it to cause some plugins to function incorrectly. To my surprise it's still useful in several use cases after 5 years of WordPress updates. Thanks for the comments everyone!