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wp_kses( string $content, array[]|string $allowed_html, string[] $allowed_protocols = array() ): string

Since
1.0.0
Source
wp-includes/kses.php:747

Removes any HTML tags, attributes, and URL protocols from a string that are not explicitly allowed by the arguments you pass in. The allowed list can be a full array of tag and attribute rules or a shorthand context name such as 'post', and the third argument narrows which URL schemes survive in things like href and src. Reach for wp_kses_post() instead when you just need the standard post-content whitelist, since building the allowed_html array by hand is easy to get subtly wrong.

Filters text content and strips out disallowed HTML.

Description

This function makes sure that only the allowed HTML element names, attribute names, attribute values, and HTML entities will occur in the given text string.

This function expects unslashed data.

Compatibility

WordPress
since 1.0.0
PHP
7.4–8.6-dev
  • 6.7.7
  • 6.8.8
  • 6.9.7
  • 7.0.4
  • 7.1.0

Present in every tracked release (6.7.7 to 7.1.0), and compiles on PHP 7.4 through 8.6-dev.

Parameters

$contentstring
Text content to filter.
$allowed_htmlarray[]|string
An array of allowed HTML elements and attributes, or a context name such as 'post'. See wp_kses_allowed_html() for the list of accepted context names.
$allowed_protocolsstring[]optional
Array of allowed URL protocols.
Defaults to the result of wp_allowed_protocols().Default: array()

Return value

string
Filtered content containing only the allowed HTML.

Code examples

Every example is editable and runs in a real WordPress booted in your browser by WordPress Playground. Press Run, then edit the code: clicking away re-runs it. Nothing is sent anywhere until you do.

Sanitize arbitrary HTML input against a custom tag whitelist

Clean up a block of untrusted HTML, such as a bio field from an admin settings page, keeping only a handful of formatting tags.

$dirty_html = '<p onclick="alert(1)">Welcome <strong>friends</strong>, visit <a href="javascript:alert(1)" title="link">this page</a>.</p><script>alert("bad")</script>';

$allowed_html = array(
	'p'      => array(),
	'strong' => array(),
	'a'      => array(
		'href'  => true,
		'title' => true,
	),
);

$clean_html = wp_kses( $dirty_html, $allowed_html );

echo '<pre>' . esc_html( $clean_html ) . '</pre>';

The onclick attribute, the script tag, and the javascript: link are all stripped because they are not part of the allowed_html array or the default allowed protocols.

Filter post content with the built-in 'post' context instead of a hand-built array

Take an existing post's content, append some injected markup to simulate an unsanitized edit, and run it through wp_kses using the 'post' context shortcut.

$content = get_post_field( 'post_content', 1 );
$content .= '<script>alert("hacked")</script><img src="x" onerror="alert(1)">';

$filtered_content = wp_kses( $content, 'post' );

echo '<p>Original length: ' . esc_html( strlen( $content ) ) . '</p>';
echo '<p>Filtered length: ' . esc_html( strlen( $filtered_content ) ) . '</p>';
echo '<pre>' . esc_html( $filtered_content ) . '</pre>';

Passing 'post' as $allowed_html uses the same rules wp_kses_allowed_html() returns for normal post content, which is usually easier to keep correct than maintaining your own array.

Common problems and fixes · 4

Why did wp_kses() strip out every single tag from my content?

The second argument is not optional and is not a blacklist. If $allowed_html is an empty array, or a variable that evaluates to one, wp_kses_split() treats no elements as allowed and removes every tag, leaving only text.

Why does my <a> tag survive but its href attribute keeps disappearing?

Allowing a tag name in $allowed_html does not automatically allow its attributes. Each attribute has to be listed under that tag as its own key.

Why do quotes and backslashes come out mangled after I run $_POST data through wp_kses()?

The docblock states this function expects unslashed data. wp_kses_no_null() and wp_kses_normalize_entities() operate on the content as-is, so slashed input straight from $_POST produces corrupted quotes and backslashes.

Is it safe to call wp_kses() on every post in a loop on every page load?

wp_kses_split() does full regex-based tokenization of the string each time it runs, which is real work for large content and adds up when repeated on every request across many posts.

Alternatives and related functions

wp_kses_post
When the content is ordinary post content and you want the same allowed tags and attributes core uses for posts, without building an $allowed_html array yourself.
wp_filter_post_kses
When you need a ready-made callback for a content-filtering hook that applies the 'post' context, rather than calling wp_kses() manually inside your own function.
sanitize_text_field
When the value should contain no HTML at all, such as a plain-text title or slug, rather than a filtered subset of tags.
esc_html
When you are only outputting a value and want it displayed as literal text, not interpreted as markup, rather than letting some tags through.

Performance profile

How much work a call to wp_kses() does, and what it touches: the algorithmic scaling, the Zend instruction count per call across PHP versions, the hooks it hands control to, and the core code that calls it. Measured from the compiled opcodes, not a stopwatch, so every number is identical on any machine running the same PHP version, and every function in core is ranked by cost.

Cost class
Trivial

Touches nothing outside its own arguments.

Scaling
Constant

No loop in the body: the same number of instructions runs whatever you pass in.

Instructions
26–29

Executed per call on PHP 8.5, depending on the branch taken. The body compiles to 29.

Plugin surface
None

Nothing here hands control to plugin code.

Called by
35

35 places in core call this, so the cost is paid more often than your own code shows.

What it touches

  • hookthird-party callbacksapply_filters()one call below wp_kses()

What one call costs · 2 distinct outcomes

One number would be a lie: the work depends on which branch runs. These are every distinct cost wp_kses() can have, taken from its control-flow graph on PHP 8.5.

WhenInstructionsCalls it makes
!empty($allowed_protocols)26wp_kses_no_null(), wp_kses_normalize_entities(), wp_kses_hook(), wp_kses_split()
empty($allowed_protocols)29wp_allowed_protocols(), wp_kses_no_null(), wp_kses_normalize_entities(), wp_kses_hook(), wp_kses_split()

Across PHP versions

Compiles the same on PHP 7.4, 8.1, 8.2, 8.3, 8.4, 8.5 and 8.6-dev: 29 instructions, 26–29 executed per call, 1 branch. The work does not change between versions.

An instruction is not a fixed amount of time, so a matching count is not necessarily the same speed; what it rules out is a difference in the work itself.

Uses · 5

Used by · 35

Show all 35

Source code

View on Trac View on GitHub 

function wp_kses( $content, $allowed_html, $allowed_protocols = array() ) {	if ( empty( $allowed_protocols ) ) {		$allowed_protocols = wp_allowed_protocols();	} 	$content = wp_kses_no_null( $content, array( 'slash_zero' => 'keep' ) );	$content = wp_kses_normalize_entities( $content );	$content = wp_kses_hook( $content, $allowed_html, $allowed_protocols ); 	return wp_kses_split( $content, $allowed_html, $allowed_protocols );}

Changelog

Introduced in 1.0.0. Unchanged from 6.7.7 through 7.1.0.

  1. 6.7.7
  2. 6.8.8
  3. 6.9.7
  4. 7.0.4
  5. 7.1.0

Signature, return type and hooks compared across 5 parsed releases.

About this page

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Generated from the wordpress-develop 6.8.8 tag, from src/wp-includes/kses.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.
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