diff --git a/highlight-html.php b/highlight-html.php
new file mode 100644
index 0000000000000..8aa954373c604
--- /dev/null
+++ b/highlight-html.php
@@ -0,0 +1,146 @@
+<?php
+
+require_once __DIR__ . '/src/wp-load.php';
+
+define( 'C_TEXT', "\e[m" );
+define( 'C_REF', "\e[38;2;154;110;58m" );
+define( 'C_COMMENT', "\e[38;2;112;128;144m" );
+define( 'C_SYNTAX', "\e[38;2;153;153;153m" );
+define( 'C_TAGNAME', "\e[38;2;153;0;85m" );
+define( 'C_ANAME', "\e[38;2;102;153;0m" );
+define( 'C_AVALUE', "\e[38;2;0;119;170m" );
+
+$options = getopt( 'fu:' ); // How rude!
+$do_format = isset( $options['f'] );
+
+$uri = 'php://stdin';
+if ( isset( $options['u'] ) ) {
+	$uri = $options['u'];
+	if ( ! preg_match( '~^https?://~', $uri ) ) {
+		$uri = "https://{$uri}";
+	}
+}
+
+$html = file_get_contents( $uri );
+
+$p = new WP_HTML_Tag_Processor( $html );
+while ( $p->next_token() ) {
+	switch ( $p->get_token_type() ) {
+	case '#comment':
+		echo C_COMMENT . '<!--' . $p->get_modifiable_text() . '-->';
+		break;
+
+	case '#doctype':
+		echo C_SYNTAX . '<!DOCTYPE' . $p->get_modifiable_text() . '>';
+		break;
+
+	case '#tag':
+		print_tag( $p );
+		break;
+
+	case '#text':
+		print_text( $p );
+		break;
+
+	default:
+		die( "Unsupported syntax: {$p->get_token_type()}" );
+	}
+}
+
+echo "\e[m\n";
+
+function print_text( $p ) {
+	$text = $p->get_modifiable_text();
+	$text = preg_replace_callback(
+		'~&(?:#\d+|#x[a-f0-9]+|[a-z]+);?~i',
+		fn ( $m ) => C_REF . $m[0] . C_TEXT,
+		$text
+	);
+
+	echo C_TEXT . $text;;
+}
+
+function print_tag( $p ) {
+	global $do_format;
+
+	static $depth = 0;
+
+	$tag_name  = $p->get_tag();
+	$is_closer = $p->is_tag_closer();
+	$closer    = $is_closer ? '/' : '';
+	$is_void   = WP_HTML_Processor::is_void( $tag_name );
+	$voider    = $is_void ? '/' : '';
+
+	if ( $is_closer && in_array( $tag_name, [ 'HEAD', 'BODY', 'OL', 'UL', 'DIV' ], true ) ) {
+		$depth--;
+	}
+
+	$indent = str_pad( '', $depth * 2, ' ' );
+
+	if ( $do_format && (
+		(
+			! $is_closer && in_array( $tag_name, [
+				'DIV', 'P', 'UL', 'OL', 'DETAILS', 'SVG', 'PATH', 'G',
+				'LINK', 'META', 'HTML', 'HEAD', 'BODY', 'TITLE', 'TEXTAREA',
+				'PRE', 'H1', 'H2', 'H3', 'H4', 'H5', 'H6', 'HGROUP',
+				'PICTURE', 'SOURCE', 'FIGURE', 'FORM', 'TABLE', 'TR',
+				'FIGCAPTION', 'BLOCKQUOTE', 'OBJECT', 'EMBED', 'IFRAME',
+				'SCRIPT', 'STYLE', 'NOSCRIPT', 'NAV', 'LI'
+			], true )
+		) || (
+			$is_closer && in_array( $tag_name, [
+				'HEAD', 'HTML', 'BODY', 'PICTURE', 'FIGURE', 'TABLE'
+			], true  )
+		)
+	) ) {
+		echo "\n{$indent}";
+	}
+	echo C_SYNTAX . '<' . $closer;
+
+	echo C_TAGNAME . strtolower( $p->get_tag() );
+	$attributes = $p->get_attribute_names_with_prefix( '' ) ?? array();
+
+	foreach( $attributes as $name ) {
+		$value = $p->get_attribute( $name );
+
+		echo ' ' . C_ANAME . $name;
+		if ( true === $value ) {
+			continue;
+		}
+
+		echo C_SYNTAX . '="';
+		echo C_AVALUE . str_replace( '"', '&quot;', $value );
+		echo C_SYNTAX . '"';
+	}
+	echo C_SYNTAX . '>';
+
+	$text = $p->get_modifiable_text();
+	if ( ! empty( $text ) ) {
+		echo 'TITLE' === $p->get_tag() ? C_TEXT : C_COMMENT;
+
+		$add_newlines = (
+			$do_format &&
+			strlen( trim( $text ) ) > 0 &&
+			(
+				'SCRIPT' === $tag_name ||
+				'STYLE' === $tag_name ||
+				'TEXTAREA' === $tag_name ||
+				'PRE' === $tag_name
+			)
+		);
+
+		if ( $add_newlines ) {
+			echo "\n" . trim( $text, "\n" ) . "\n";
+		} else {
+			echo $text;
+		}
+
+		echo C_SYNTAX . '</' . C_TAGNAME . strtolower( $p->get_tag() ) . C_SYNTAX . '>';
+	} elseif ( in_array( $tag_name, [ 'SCRIPT', 'STYLE', 'TEXTAREA', 'PRE' ], true ) ) {
+		echo C_SYNTAX . '</' . C_TAGNAME . strtolower( $p->get_tag() ) . C_SYNTAX . '>';
+	}
+
+	if ( ! $is_closer && in_array( $tag_name, [ 'HEAD', 'BODY', 'OL', 'UL', 'DIV' ], true ) ) {
+		$depth++;
+	}
+}