WordPress Development – Filters

Filters are one of the two types of hooks. With Filters it is possible to change data during the execution of WordPress Core, Plugins and Themes and are therefore the counterpart to Actions. Filters work in isolation and therefore have no side effects, such as affecting global variables and outputs.


Add a Filter

To add a filter, it requires two steps.

  1. Creating a callback function that will be called when the filter is executed.
  2. Adding the callback function to a hook that performs the call to the function.

When adding a filter, use the add_filter() with at least two parameters:

  • string $hook_name, the name of the filter that will be included.
  • callable $callback the name of the callback function.

In the following example, the code is executed when the filter the_title is executed.

function arrowdesign_filter_title( $title ) {
return 'The ' . $title . ' was filtered';
add_filter( 'the_title', 'arrowdesign_filter_title' );

For example, if you have a post with a title “Learn WordPress”, it will be changed to “Learn WordPress has been filtered”.


Additional Parameters

add_filter() can accept two additional parameters:

  • int $priority for the priority given to the callback function.
  • int $accepted_args for the number of arguments given to the callback function



In this example, a CSS class is added to the <body> tag if a certain condition is met.

function arrowdesign_css_body_class( $classes ) {
if ( ! is_admin() ) {
$classes[] = 'arrowdesign-is-awesome';
return $classes;
add_filter( 'body_class', 'arrowdesign_css_body_class' );


We hope this WordPress Development – Filters post was helpful and you now know how to use filters on your own website. You can find more articles here:


Read another WordPress post : ‘WordPress Development – Hooks

For more excellent information on this topic, visit developer.wordpress.org


Arrow Design, based in Dublin, Ireland, provides quality website design services in Dublin and beyond at affordable prices. If you would like help with implementing the above code, or any wordpress website development project, contact us. We love website design and it shows! We provide custom wordpress plugin development, website design training and lots more.

We do it all, so you don’t have to!

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